SMITHSONIAN CONTRIBUTIONS TO BOTANY NUMBER 78 

Vascular System of the 

Male and Female Florets 

of Raddia brasiliensis 

(Po ace ae : B ambu soideae : 01 yre ae) 

Thompson Demetrio Pizzolato 

SMITHSONIAN INSTITUTION PRESS 

Washington, D.C. 

1990 
ABSTRACT 

Pizzolato, Thompson Demetrio. Vascular System of the Male and Female Florets of Raddia 

brasiliensis (Poaceae: Bambusoideae: Olyreae). Smithsonian Contributions to Botany, number 

78,32 pages, 23 figures, 1 table, 1990.-The components of the vascular systems in the male 

floret and the female floret of Raddia are described from reconstructed serial, transverse 

sections. Squat tracheary elements, sieve elements, and intermediary cells comprise the systems. 

The male floret has six and the female floret three collateral bundles in the rachilla at the floret 

base that become interconnected into a lower sieve-element plexus with accompanying 

tracheary elements. Besides contributing to the lower plexus, the rachilla bundles serve as the 

traces for the lemma and palea. That bundle (bundle 3) which is the trace for the lemma median 

contributes most of the sieve and tracheary elements to the lower plexus. Supernumerary 

bundles are associated with bundle 3. Rising in the rachilla from the lower plexus is the upper 

plexus of sieve and tracheary elements. The circular form of the upper plexus of the male floret 

is influenced by the two traces from each of the anterior lodicules and by each trace from the 

three stamens. The trace from the posterior lodicule of the male and female florets does not 

influence the upper plexus. The bi-arcuate form of the upper plexus of the female floret is 

influenced by the two, more posterior traces from the anterior lodicules. The three staminodia in 

the female floret do not influence the upper plexus because they are avascular. At the pistil base 

is a massive amphicribral bundle, the pistil plexus, that sends down vascular prongs and lobes 

to merge with the upper and lower plexi. Two posterolateral (stylar) collateral bundles merge 

with the pistil plexus in a gynobasic manner. A placental bundle ascends from the posterior of 

the pistil plexus, merges with the chalaza, and exceeds the tip of the ovule before ending in a 

stylar core. Components of the floret vascular system of Raddia confirm the Olyreae as a tribe 

of the Bambusoideae that should not be placed in the subfamilies Festucoideae, Oryzoideae, or 

Panicoideae. 

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is 

recorded in the Institution’s annual report, Smithsonian Year. SERIES COVER DESIGN: Leaf 

clearing from the katsura tree Cercidiphyllum japonicum Siebold and Zuccarini. 

Library of Congress Cataloging-in-Publication Data 

F’izzolato, Thompson Demetrio 

Vascular system of the male and female florets of Raddia brasiliensis (Poaceae:Bambusoideae:Olyreae) / Thompson 

Demetrio Pizzolato. 

p. 

Includes bibliographical references. 

Supt of Docs. no.: SI 1.29:78 

1. Raddia Brasiliensis. 2. Flowers. 3. Vascular system of plants. I. Title. 11. Series. 

cm.--(Smithsonian contributions to botany ; no. 78) 

QKlS2747 M. 78 [QK492.G74] 581 s-dc20 [584’.93] 90-10223 
Contents 

Page 

Introduction ....................................... 1 

Materials and Methods ............................... 7 

Acknowledgments ................................. 7 

Vascular Morphology of the Male Floret ........................ 7 

Vascular Anatomy of the Male Floret .......................... 9 

Vascular Morphology of the Female Floret ....................... 12 

Vascular Anatomy of the Female Floret ........................ 14 

Comparative and Phylogenetic Considerations ..................... 19 

Components of the Floret Vascular System of Raddia Are Compared to Those 

Known in the Festucoideae and Oryzoideae .................... 19 

Floret Vascular Anatomy Suggests that Raddia Belongs to the Olyreae of the 

Bambusoideae ................................... 24 

Floret Vascular Anatomy Suggests that Raddia and the Olyreae Are Not Panicoid 

Grasses ....................................... 27 

Floret Vascular Anatomy Suggests that Brachyelytrum Is Not an Olyroid 

Grass ........................................ 29 

Floret Vascular Anatomy Suggests that Raddia and the Olyreae Are Not Oryzoid 

Grasses ....................................... 29 

Literature Cited ..................................... 31 

iii 

Vascular System of the 

Male and Female Florets 

of Raddia brasiliensis 

(Poaceae: Bambusoideae: Olyreae) 

Thompson Demetrio Pizzolato 

Introduction 

Early anatomists investigating the florets of grasses such as 

Arber (1934), Be& (1939), Chandra (1962), and Butzin (1965) 

were compelled by the lack of techniques to treat the 

vasculature of the floret axis as if it were a homogenous mass 

of tissue whose only variation was the number of branches or 

traces it sent into the appendages of the floret. However, 

techniques of light microscopy such as glutaraldehyde fixation, 

plastic embedding, and thin sectioning (not available to earlier 

workers) suggested to Zee and O’Brien (1970) that the vascular 

tissue of the grass floret, instead of being homogeneous, 

contained organized and discrete components with generic 

constancy or variability. The analyses of serial cross sections 

by Zimmermann and Tomlinson (1972) and Larson (1975) 

revealing three-dimensional vascular organization in large 

stems of other angiosperms indicated further that these newer 

techniques similarly should reveal the systems in the compact 

stems of grass florets. Zimmermann and Tomlinson (1972), 

Larson (1975), and Hitch and Sharman (1968, 1971) in their 

studies of the vegetative stems of grasses, also demonstrated 

that the components of a mature three-dimensional vascular 

system are delimited best after a developmental study shows 

how the components of the system are blended together. Aided 

by such techniques and ideas, a few anatomists have begun 

studying anew the vasculature of the grass floret at anthesis. 

One or more florets are arranged distichously on the axis or 

rachilla of the spikelet, the basic unit of the grass inflorescence 

(Gould and Shaw, 1983). The floret consists of two alternate 

bracts, the proximal lemma and the distal palea, and the flower 

they subtend. The grass flower usually consists of two scales or ~~ ~ 

Thompson Demetrio Pizzolato, Delaware Agricultural Experimenr 

Station, Department of Plant and Soil Sciences, College of Agricultural Sciences, University of Delaware, Newark, Delaware 1971 7- 

1303. 

lodicules subtending a few stamens and a pistil. Because the 

axis of the floret is a continuation of the rachilla of the spikelet, 

the axis in the floret is designated the rachilla also (RobinsonBeers and Pizzolato, 1987a). 

Means of studying the vascular system of a floret rachilla 

involve tracing with the aid of a microscope drawing tube the 

various vascular tissues from serial cross sections, transferring 

the tracings to plastic sheets, and reconstructing the various 

systems into a three-dimensional model or facsimile by 

superimposing the vascular tracings (Pizzolato, 1983, 1984, 

1988; O’Brien et al., 1985). The components of the vascular 

systems are discerned through study of the facsimiles. 

Comparisons among the various rachillae continue and more 

features are revealed as more models are generated and studied. 

If there is interest in using the revealed components of the 

vascular systems to test phylogenetic relationships as French 

and Tomlinson (1983) have done concerning stems of the 

Araceae, natural systems of grass classification are found in the 

works of Soderstrom and Ellis (1987), Watson et al. (1985), 

Macfarlane and Watson (1982), and Hilu and Wright (1982). 

The system of Hilu and Wright (1982) recognizes a large 

subfamily, the Festucoideae, to include genera previously 

assigned to triticoid, agrostoid, festucoid, avenoid, and phalaroid groups. In this discussion, festucoid and Festucoideae are 

used in the sense of Hilu and Wright (1982). Four of the 

festucoid genera analyzed for the floret vascular system are 

closely related according to their scheme: Anthoxanthum L., 

1753, (Pizzolato, 1984; Pizzolato and Robinson-Beers, 1987; 

Robinson-Beers and Pizzolato, 1987a, b, c) Alopecurus L., 

1753, (Pizzolato, 1987), Phleum L., 1753, (Pizzolato, 1988), 

and Phalaris L., 1753, (Pizzolato, 1989a). Triticum L., 1753, 

(Zee and O’Brien, 1970; O’Brien et al., 1985) is related more 

distantly to these four. Leersia Swartz, 1788, (Pizzolato, 

1989b), which is placed into a distinct subfamily, the 

Oryzoideae, by Hilu and Wright (1982) is the least related of 

1 
2 

the five genera sufficiently studied. Only one species of each of 

these six genera has been analyzed, so the systematic value of 

any component of the vascular system hardly can be 

appreciated. However, even this survey indicates that some 

components of the vascular system are more constant across the 

genera than others. 

Before the components of the vascular system are enumerated, the tissues composing the vascular system are described 

primarily from the observations of Triticum (Zee and O’Brien, 

1970; O’Brien et al., 1985) and Anthoxunthum (Pizzolato, 

1984; Robinson-Beers and Pizzolato, 1987a, b, c; Frick and 

Pizzolato, 1987), which agree with the observations in the other 

genera studied. The sieve elements are enucleate at maturity 

and in every way normal except that they tend to be shorter and 

narrower than those in stems. Callosed pores often are clustered 

into sieve areas on walls serving as sieve plates, and sieve tubes 

composed of sieve-tube members are found. However, because 

sieve areas on sieve plates are not seen always, the less precise 

term “sieve element” (Esau, 1977) safely describes the 

conducting cell of the phloem. 

Two kinds of tracheary elements occur. The normal ones are 

usually squat with scalariform secondary thickenings on cells 

devoid of contents at maturity. Simple perforations frequently 

are difficult to identify positively. Therefore, the less precise 

term tracheary element is preferable to vessel member to 

describe the normal conducting cells of the xylem (Esau, 1977). 

The abnormal conducting cells of the xylem of the floret are 

known as the cells of the xylem discontinuity (Zee and 

O’Brien, 1970; Pizzolato, 1984; Robinson-Beers and Pizzolato, 

1987a, b, c; Frick and Pizzolato, 1987). At maturity, the cells 

comprising the xylem discontinuity resemble the normal 

tracheary elements except that their secondary walls often are 

thicker and their protoplasts are persistent; thus, these cells are 

likely poor conductors of sap (Zee and O’Brien, 1970; Frick 

and Pizzolato, 1987). 

The tracheary elements and sieve elements are contained in 

a matrix of vascular parenchyma cells extending from the 

rachilla at the base of the floret into the ovule. The cells of the 

vascular parenchyma are densely cytoplasmic and, by anthesis, 

their primary walls usually lack ingrowths. Hence, these cells 

are intermediary cells (Esau, 1977). When the intermediary 

cells are adjacent to sieve or tracheary elements and have 

developed from the same mother cell, such intermediary cells 

also serve as companion cells or contact cells (Esau, 1977). The 

vascular parenchyma cells, sieve elements, and tracheary 

elements comprising the floret vascular system is a compact 

tissue with little intercellular space. 

Before discussing the patterns in which the sieve elements 

and tracheary elements are arranged to form the various 

components of the floret vascular system, it is appropriate to 

mention the developmental principles underlying the formation 

of the segments of the vascular system. The vascular system in 

the vegetative shoot is initiated as isolated procambia that are 

the incipient traces for nearby leaf primordia. Those isolated 

procambial sites destined to become major traces are initiated 

SMITHSONIAN CONTRIBUTIONS TO BOTANY 

earlier in the stem and lower from their primordium; 

procambium to become lesser traces is initiated isolated later 

and closer to its primordium or even in it (Hitch and Sharman, 

1968; Patrick, 1972). The vascular system in the rachilla is 

initiated similarly (Maze et al., 1971, 1972; Pizzolato and 

Robinson-Beers, 1987). Upon this basic pattern of isolated 

procambia formed in relation to the primordia on the rachilla, 

all the complexity of the floret vascular system is built. 

The isolated procambia that initiate the vascular system 

develop in meristematic tissues of the young rachilla. The 

meristematic tissue in which the procambial traces develop are 

residual meristems, tissues retaining their meristematic features 

beyond the apical meristem (Esau, 1953, 1977). The major 

procambial traces are initiated when most of the young rachilla 

is composed of residual meristem (Pizzolato and RobinsonBeers, 1987). During subsequent development of the rachilla, 

most of the residual meristem disappears as it contributes cells 

to the traces of the primordia and differentiates into ground 

parenchyma (Esau, 1977; Pizzolato and Robinson-Beers, 1987; 

Robinson-Beers and Pizzolato, 1987a, b). However, two cores 

of residual meristem persist longer in the floret. One of these 

cores develops directly from the apical meristem of the 

developing floret as it becomes converted into the ovule 

primordium (Maze et al., 1971, 1972; Robinson-Beers and 

Pizzolato, 1987~). From this core of residual meristem will 

develop the several components of the vascular system related 

to the pistil. The second core of residual meristem persists 

lower in the rachilla, between the developing procambial trace 

related to the lemma primordium and the higher traces related 

to the stamen primordia (Pizzolato and Robinson-Beers, 1987). 

Sieve elements, which differentiate acropetally in procambium 

that developed from this residual meristem, connect the lemma 

trace with the stamen traces and form another component of the 

floret vascular system, the upper sieve-element plexus (Robinson-Beers and Pizzolato, 1987a, b; Pizzolato and RobinsonBeers, 1987). 

Two developmental principles underlying the formation of 

the vascular system have just been discussed: (1) its initiation 

in the residual meristem as isolated procambial traces related to 

the primordial appendages of the floret; and (2) the extended 

persistence of two cores of residual meristem, one in the pistil 

primordium, and the other lower, where it will connect the 

principal lemma trace with the stamen traces. A third 

developmental principle is that all of the initially isolated 

procambial segments in the rachilla of the floret will become 

more or less interconnected in an orderly pattern by the 

continued growth of the early procambial sites related to the 

traces and by the formation of procambium in the persistent 

cores of residual meristem. Vascular tissues will differentiate 

along these procambial paths. 

There are a number of ways in which the procambia, and the 

vascular tissues differentiating from them, grow and interconnect in the rachilla. Isolated procambial traces grow acropetally 

toward the apex of their appendage and basipetally in the 

rachilla until they merge with strands of a lower component of 
NUMBER 78 3 

I1 M 

ANTERIOR 

I pp 

} USEP 

} LSEP 

3 

POSTERIOR 

A 

I ST 

) SRB 

3 

ANTERIOR POSTERIOR 

B 

FIGURE 1 .--Diagrams of major components of typical floret vascular systems. A. Festucoideae. At floret base one 

or several vascular bundles occur in the rachilla. These are traces to major veins of lemma and palea. The principal 

bundle is bundle 3, which is the trace for the lemma median (M). At the emergence of the bundles from rachilla 

to bracts, sieve elements from the bundles interconnect into the lower sieve-element plexus (LSEP). Sieve 

elements of the LSEP merge into the upper sieve-element plexus (USEP). Many of the sieve elements of the 

USEP come from the vicinity of M. Because the USEP is the vascular system of the stamens, it is bilobed with 

two stamens and trilobed with three. At the pistil base, below the ovule, is the pistil plexus (PP). It is connected 

by vascular bundles (prongs) to the USEP between the emergences of the stamen traces. If the USEP is bilobed. 

the pistil plexus connects with two prongs. If the USEP is trilobed, the pistil plexus connects with three. The 

anterior sieve tube (A) connects at the anterior of the pistil plexus. Only the sieve elements at the posterior of the 

pistil plexus ascend to contribute sieve elements to the placental bundle (PB), which develops between the 

attachments of the posterolateral sieve tubes (PL). The placental bundle supplies the ode. The posterolaterals 

supply the styles. The xylem discontinuity (XD), a system of anomalous tracheary elements, replaces all normal 

tracheary elements above bundle 3. The xylem discontinuity complements the sieve elements in all other 

components except A and PL. 

B. Orymideae. A xylem discontinuity does not occur; normal tracheary elements accompany all sieve elements. 

There is no lower sieve-element plexus because sieve and tracheary elements of the sole rachilla bundle (SRB) 

interconnect in becoming the median trace of the lma (M). Hence, SRB is like bunde 3 in the Festucoideae. 

No upper sieve-element plexus occurs but only a system of stamen traces (ST), which weakly link horizontally 

before merging with the posterior of SRB. The pistil plexus (PP) connects weakly between the stamen traces by 

one vascular bundle (prong). The placental bundle (PB) is more narrow than that in the Festimideae. The 

posterolaterals (PL) do not attach high at the PB but near the anterior of PP instead of an anterior bundle. 

the system (Maze et al., 1971, 1972; Pizzolato and RobinsonBeers, 1987; Robinson-Beers and Pizzolato, 1987a, c). Horizontal interconnections or short circuits form between more 

axially arranged procambial strands by the differentiation of 

procambium from the intervening parenchyma or meristematic 

cells (Hitch and Shaman, 1971; Robinson-Beers and Pizzolato, 1987a). As the vascular tissues differentiate, they may 

shunt from one procambial strand through a procambial bridge 

to another procambial strand and use that strand for a further 

path of differentiation (Robinson-Beers and Pizzolato, 1987a). 

Interconnections can occur also as adjacent horizontal and 

vertical procambia increase in girth by converting surrounding 

parenchyma or meristematic cells into procambia, and thus 

grow together (Dengler et al., 1985; Robinson-Beers and 

Pizzolato, 1987a). Vascular tissue differentiating in one of the 

strands can differentiate into the newly fused neighboring 

strand. This last means of interconnection is how one of the 

main components of many vascular systems, the lower 

sieve-element plexus, arises (Robinson-Beers and Pizzolato, 

1987a). 

Discussion of the developmental principles underlying the 

initiation and interconnection of the components of the floret 

vascular system is followed now by an introduction to the 

segments themselves. The components of the festucoid genera 

will be discussed first because they are more alike, and then 

they can be contrasted together with the components of oryzoid 

florets. Continual reference to the diagrams of the festucoid 

(Figure 1~) and oryzoid (Figure 1B) systems and to the figures 
4 SMITHSONIAN CONTRIBUTIONS TO BOTANY 

in the cited works will be helpful. The discussion begins with 

the number of vascular bundles in the rachilla at the base of the 

floret. 

That bundle number is one to several. Three may be a 

frequent number (Arber, 1934; Pizzolato, 1984). The bundles 

are the basipetal portions of major traces for the lemma only or 

for the lemma and palea (Robinson-Beers and Pizzolato, 

1987a; Pizzolato and Robinson-Beers, 1987; Pizzolato, 1987, 

1988, 1989a). The solitary bundle or the principal bundle 

(bundle 3) is the basipetal portion of the median trace of the 

lemma 0. Bundle 3 is usually collateral with its tracheary 

elements between its sieve elements and the lemma; that is, the 

transverse axes of the xylem and the phloem in bundle 3 are 

perpendicular to the lemma. Some of the other bundles are 

composite bundles of two fused lemma or palea traces. 

The significance to the vascular system of more than one 

bundle in the rachilla is that sieve elements from these separate 

bundles horizontally link higher in the rachilla forming the 

segment designated the lower sieveelement plexus. Therefore 

Anthoxanthum, Phleum, Phalaris, and Triticum have the lower 

sieve-element plexus in the rachilla above the separate rachilla 

bundles, but Alopecurus with one rachilla bundle does not 

(Pizzolato, 1984, 1987, 1988, 1989a; Robinson-Beers and 

Pizzolato, 1987a; O’Brien et al., 1985). The lower sieveelement plexus is a peripheral, horizontal network of sieve 

elements interconnecting the axial rachilla bundles as they bend 

toward the lemma and palea or toward the lemma alone to 

become the major traces of these appendages. As bundle 3 turns 

into the lemma median, it always extensively contributes sieve 

elements to the lower sieve-element plexus. 

Higher in the rachilla, above the divergence of the lemma 

and palea traces, another sieveelement plexus occurs, the 

upper sieve-element plexus. The lower sieve-element plexus 

(or phloem from the solitary rachilla bundle of Alopecurus) 

merges in various patterns into the upper sieve-element plexus 

(Pizzolato, 1984, 1987, 1988, 1989a). The upper sieve-element 

plexus first serves as the phloem system of the stamens in the 

rachilla. Because it forms under the influence of the stamens 

(Pizzolato and Robinson-Beers, 1987; Robinson-Beers and 

Pizzolato, 1987b) from a residual meristem in the internode 

between the stamen insertions and the median trace to the 

lemma (M), the upper sieve-element plexus is a hollow, 

vaselike, bi- or trilobed network of sieve elements arising from 

the vicinity of M (Pizzolato, 1984, 1987, 1988, 1989a). When 

O’Brien et al. (1985) recognized this component of the floret 

vascular system in Triticum, they did not realize its initial 

function as the vascular system for the stamens. After anthesis 

the upper sieve-element plexus is the link between the lower 

sieve-element plexus and the next higher segment of the floret 

vascular system, the pistil plexus. 

The pistil plexus is a horizontal ring of interconnected sieve 

elements at the base of the pistil (O’Brien et al., 1985; 

Robinson-Beers and Pizzolato, 1987c; Pizzolato, 1987, 1988, 

1989a). All components of the floret vascular system related to 

the pistil develop from procambium differentiating in a residual 

meristem persisting from the apical meristem (Holt, 1954; 

Sharman, 1960a, b; Maze et al., 1971, 1972; Robinson-Beers 

and Pizzolato, 1987~). The pistil plexus is connected to the 

upper rim of the upper sieve-element plexus by basipetally 

differentiating vascular bundles in the form of prongs that 

merge with the upper sieve-element plexus between the sites 

where the stamen traces diverge (Robinson-Beers and Pizzolato, 1987~). Therefore, a bistaminate upper plexus is linked to 

the pistil plexus by two prongs, and a tristaminate one by three 

prongs (Pizzolato, 1984, 1987, 1988, 1989a). At the anterior 

(the lemma side) of the pistil plexus, a single sieve tube 

develops and supplies the anterior of the pistil (RobinsonBeers and Pizzolato, 1987~). This sieve tube is recognized as a 

component of the floret vascular system, the anterior sieve tube 

(Aziz, 1978, 1981; Pizzolato, 1984, 1987, 1988, 1989a; Lingle 

and Chevalier, 1985). Because they did not recognize its 

segments, O’Brien et al. (1985) designated the continuum of 

lower sieve-element plexus, upper sieve-element plexus, and 

pistil plexus as a unit, or “phloem annulus.” 

The sieve elements at the posterior of the pistil plexus merge 

into the next component of the floret vascular system, the 

placental bundle. The placental bundle is the last segment of the 

floret vascular system to differentiate (Aziz, 1972, 1978, 1981; 

Lingle and Chevalier, 1985; Robinson-Beers and Pizzolato, 

1987~). The sieve elements of the placental bundle differentiate 

in the posterior of the ovary between the sieve elements coming 

from the styles, the posterolaterals. The sieve elements of the 

placental bundle become united with the posterolaterals and the 

sieve elements in the posterior of the pistil plexus (RobinsonBeers and Pizzolato, 1987~). Rising from the pistil plexus, the 

sieve elements of the placental bundle fan out in the posterior 

of the pistil, diminish, and at anthesis, end about the base of the 

chalaza. The chalaza is that region of the ovule where its cells 

are continuous from the embryo sac to the posterior of the 

ovary without intervening epidermises of nucellus, inner 

integument, outer integument, and inner posterior ovary wall 

(Pizzolato, 1984). The placenta has a higher and broader area, 

includes the chalaza, and is the region of contact between the 

young seed and the inner posterior ovary wall. 

Besides the sieve elements and the cells of the xylem 

discontinuity, the placental bundle has an abundance of 

intermediary cells continuous with those in the lower components. In the distal regions of the placental bundle, most of the 

intermediary cells are located horizontally between the ovule 

and diminishing sieve elements of the placental bundle 

(Pizzolato, 1984, 1987, 1988, 1989a). The intermediary cells 

continue distally beyond their associated sieve elements to 

blend with those at the chalazal end of the nucellus. Hence, by 

means of its intermediary cells, as the placental bundle ascends 

and departs the posterior ovary wall, it terminates by blending 

with the nucellus of the young seed (Pizzolato, 1984, 1987, 

1988,1989a). The distalmost intermediary cells of the placental 

bundle end in the chalaza by merging with the intermediary 
NUMBER 78 5 

cells of the nucellus because the placental bundle and nucellus, 

both in continuity, originate from the residual meristem that 

persists in the tip of the floret from the apical meristem 

(Robinson-Beers and Pizzolato, 1987~). 

The most distal component of the floret vascular system is 

made of the sieve elements in or near each of the two styles, the 

posterolaterals. The attachments of the posterolaterals to the 

flanks of the placental bundle set a convenient, albeit 

imprecise, proximal limit to the placental bundle of festucoid 

grasses (Pizzolato, 1988, 1989a). The sieve elements of the 

posterolaterals mature before those of the placental bundle 

when they originate in isolation near the styles and differentiate 

basipetally (Aziz, 1978,1981) toward the posterior of the pistil 

plexus. 

Until now the phloem of the components of the floret 

vascular system has been discussed. The tracheary elements in 

the floret vascular system are of two types. The vascular 

bundles in the rachilla at the base of the floret contain normal 

tracheary elements. These do not continue up the rachilla 

beyond the lower sieve-element plexus because they leave the 

rachilla as they enter the lemma and palea traces (Pizzolato, 

1984, 1987, 1988, 1989a). Just above the entrance of the 

median trace into the lemma from the rachilla, all normal 

tracheary elements in the rachilla are superseded by the 

abnormal tracheary elements of the xylem discontinuity. The 

base of the xylem discontinuity occurs in the rachilla in 

continuity with a few normal tracheary elements that continue 

in the rachilla for a few micrometers above the emergence of 

the lemma median; the xylem discontinuity now occurs instead 

of a system of normal tracheary elements. In other words, the 

xylem discontinuity begins in the rachilla immediately above 

the median lemma trace at the level where the lower 

sieve-element plexus is beginning to merge with the upper 

sieve-element plexus (Pizzolato, 1984, 1987, 1988, 1989a). 

The xylem discontinuity is thus surrounded by these peripheral 

sieve-element networks. Intermediary cells constitute the 

matrix of these three components. The xylem discontinuity at 

this level is differentiated from procambium developing from 

the core of residual meristem persisting in the rachilla above the 

emergence of M this is the same core from which differentiated the upper sieveelement plexus (Robinson-Beers and 

Pizzolato, 1987b; Pizzolato and Robinson-Beers, 1987). 

The xylem discontinuity is restricted to the center of the 

rachilla below the exits of the stamen traces from the upper 

sieve-element plexus into the stamens. At the level of the two 

or three stamen traces, the cells of the xylem discontinuity 

follow the phloem into the traces (Pizzolato, 1984,1987,1988, 

1989a). However, the rachilla is not devoid of the xylem 

discontinuity above the exit of the stamen traces. The xylem 

discontinuity now occurs as the xylem complement of those 

two or three prongs of vascular tissues that develop from the 

pistil plexus and merge basipetally with the upper sieveelement plexus between its emerging stamen traces (Pizzolato, 

1984, 1987, 1988, 1989a; Robinson-Beers and Pizzolato, 

1987b). 

The cells of the xylem discontinuity ascend from within the 

upper sieve-element plexus into each prong and then into the 

area within the enveloping sieve elements of the pistil plexus at 

the base of the pistil (Robinson-Beers and Pizzolato, 1987c; 

Pizzolato, 1984, 1987, 1988, 1989a). Surrounded by the pistil 

plexus, the xylem-discontinuity cells from the prongs coalesce 

toward the posterior of the pistil plexus. As the tracheary 

elements of the xylem discontinuity rise farther, they fan out in 

the same pattern as the sieve elements rising from the posterior 

of the pistil plexus. Therefore, the placental bundle comes to 

consist of an arc of the tracheary elements of the xylem 

discontinuity to the anterior of an arc of normal sieve elements 

in a matrix of intermediary cells. With farther ascent toward the 

base of the chalaza, the xylem discontinuity of the placental 

bundle diminishes and usually ends more proximally than its 

sieve elements. Although the xylem discontinuity becomes a 

part of the traces to the stamens, it does not enter the anterior 

bundle or the posterolateral bundles of the pistil. Although the 

component was designated first with the preferred “xylem 

discontinuity” by Zee and O’Brien (1970789), it has more 

recently been designated “xylem block” in Triticum by O’Brien 

et al. (1985507). 

Although the above description summarizes the major 

components of the floret vascular system in the sampled 

festucoid species, a few minor components remain to be 

discussed. They are designated as minor because they do not 

appear to influence the formation of the other components 

(Pizzolato, 1989a). These minor components include the lesser 

traces for the lemma and palea and the trace system from the 

lodicules. Lodicule traces apparently differentiate from the 

lodicule into the rachilla and connect with the rest of the floret 

vascular system at the anterior of the lower sieve-element 

plexus (Pizzolato, 1989a). Although each lodicule often has 

only one trace, which lacks xylem, some genera differ in both 

features (Pissarek, 1971; Craig and O’Brien, 1975; Pizzolato, 

1989a). Last are the short anterolateral sieve tubes that in a few 

genera connect to each flank of the placental bundle more 

proximally than the posterolaterals @elk, 1939; Chandra, 

1963; Pizzolato, 1989a). 

Although there are generic variations among the floret 

vascular systems of the festucoid grasses, they share seven 

major components that have common ontogenies: (1) a lower 

sieve-element plexus joining multiple bundles in the rachilla at 

the base of the floret, (2) an upper sieve-element plexus related 

to the stamens, (3) a pistil plexus connected by prongs to the 

upper sieve-element plexus, (4) a sieve tube at the anterior of 

the pistil plexus, (5) a placental bundle rising from the posterior 

of the pistil plexus, (6) posterolaterals from the styles 

delimiting the placental bundle, and (7) a xylem discontinuity 

complementing all these components but the anterior and 

posterolateral bundles. 

If these festucoid components are sought in the oryzoid 
6 SMITHSONIAN CONTRIBUTIONS TO BOTANY 

grasses Leersia (Belk, 1939; Piuolato, 1989b) and Oryza L., 

1753, (Zee, 1972; Kawahara et al., 1977), distinctions between 

the groups appear so striking that they favor more study to 

reveal the principal distinctions among the other great clusters 

of grasses. Therefore, the components of the vascular system, 

primarily of the floret of Leersia (Pizzolato, 1989b), will be 

enumerated and contrasted with those in the festucoid vascular 

system (Figure 1). 

Leersia lacks a lower sieve-element plexus (Pizzolato, 

1989b). Of the festucoid species analyzed, only Alopecurus 

(Pizzolato, 1987) agrees with Leersia in this regard. The reason 

is that Leersia and Alopecurus have only the rachilla bundle 

related to the median trace of the lemma in the floret base, thus 

avoiding the need as in other genera to link sieve elements from 

discrete bundles before farther ascent in the rachilla. 

The arrangement of xylem and phloem in the rachilla bundle 

related to the lemma median at the floret base (bundle 3) also 

differs between the subfamilies. In the festucoids except 

Alopecurus, bundle 3 is collateral with xylem between the 

phloem and the lemma; that is, the vascular tissues are 

perpendicular to the floret’s anterior-posterior plane (Pizzolato, 

1984,1988,1989a). Bundle 3 is bicollateral in Alopecurus with 

phloem-xylem-phloem arranged parallel at the floret base to the 

anterior-posterior plane (Pizzolato, 1987). Leersia (Pizzolato, 

1989b) and apparently the oryzoid Luziola (Arber, 1928) differ 

from the festucoid group. In the rachilla at the floret base, the 

oryzoids have a single collateral bundle whose phloem and 

xylem parallel the floret’s anterior-posterior plane, and whose 

phloem envelops the xylem during ascent in the rachilla 

(Pizzolato, 1989b). In the other features to be discussed, 

Alopecurus is decidedly festucoid. 

The festucoid grasses have an upper sieve-element plexus. 

Instead, Leersia has a stamen-trace system that is nearly 

independent of the rest of its floret vascular system (Pizzolato, 

1989b). Upon entering the rachilla, the stamen traces descend 

its flanks with few horizontal interconnections between them. 

Their descent continues until they merge separately with the 

posterior of the solitary rachilla bundle, which blocks further 

descent, Compared to the upper sieve-element plexus of the 

festucoid grasses, the stamen traces of Leersia comprise a less 

integrated component in the floret vascular system (Pizzolato, 

1989b). This tendency for the stamen traces to be more 

autonomous in the oryzoid grasses than in the festucoid grasses 

aids in understanding the variability of stamen number that is 

peculiar to rices (Hilu and Wright, 1982; Watson et al., 1985; 

Tbcker, 1988). 

Festucoid genera have a xylem discontinuity. Oryzoid 

genera lack one. Zee and O’Brien (1970) and Zee (1972) made 

these discoveries, and Pizzolato (1989b) has confirmed them. 

Only normal tracheary elements accompany each and all of the 

phloem components in the Oryzoideae. 

Although the Oryzoideae and Festucoideae of Hilu and 

Wright (1982) are alike in having a pistil plexus, the plexus 

from each group is different in the number of vascular prongs 

descending from it, and in the nature of the connection that the 

prongs make with the proximal segments. Two or three prongs 

of vascular tissue descend from the festucoid pistil plexus to 

merge, between the emerging stamen traces, with the sieve 

elements of the upper sieve-element plexus and the associated 

tracheary elements of the xylem discontinuity (Robinson-Beers 

and Pizzolato, 1987c; Pizzolato, 1987, 1988, 1989a). The 

single vascular bundle descending from the oryzoid pistil 

plexus cannot merge with an upper sieve-element plexus and, 

instead, inserts itself into the area cimmscribed by the entering 

stamen traces and their tenuous, horizontal interconnections 

(Pizzolato, 1989b). The realization of this apparently less 

intimate connection correlates well with the experiments of Zee 

(1972) and Kawahara et al. (1977) showing that dyes 

introduced into the rachilla of Oryza move with difficulty into 

the pistil compared to movement into the lemma, despite the 

absence of a xylem discontinuity. On the other hand, despite 

the intimate interconnection between the festucoid pistil plexus 

and the upper sieve-element plexus, the xylem discontinuity 

prevents passage of sap through the xylem from the rachilla to 

pistil in Anthoxanthum (Frick and Pizzolato, 1987) and 

Triticum (Zee and O’Brien, 1970). As with the stamen 

components, the pistil components of the oryzoid grasses 

appear to be more nearly distinct in comparison with these 

components in the festucoid grasses. 

The festucoid and oryzoid grasses of Hilu and Wright (1982) 

are alike in that the posterior of the pistil plexus merges into the 

placental bundle that merges and ends in the nucellus at the 

chalaza (Pizzolato, 1989b). However, the oryzoid placental 

bundle lacks the xylem discontinuity, is narrower than the 

festucoid placental bundle, and matures more slowly (Pizzolato, 1989b). A more significant distinction between the 

placental bundles involves the sites of attachment of the 

posterolaterals from the styles. In festucoid genera the 

posterolaterals merge with the rest of the floret system, high 

and posteriorly, at the placental bundle (Robinson-Beers and 

Pizzolato, 1987c; Pizzolato, 1987, 1988, 1989a). In oryzoid 

genera the posterolaterals merge, low and anteriorly, at the 

pistil plexus below the ovule @elk, 1939; Kawahara et al., 

1977; Pizzolato, 1989b). Pizzolato (1989b:600) called this type 

of posterolateral attachment “gynobasic.” Apparently, the 

oryzoid tendency to keep its components somewhat distinct 

favors a longer independent basipetal course of differentiation 

before merger into the rest of the floret system. 

Composition of the posterolaterals also varies between the 

groups: oryzoid posterolaterals contain both tracheary elements 

and sieve elements; festucoid genera contain only sieve 

elements in their posterolaterals (Pizzolato, 1989b). Related to 

the attachment of the posterolaterals near the anterior of the 

pistil plexus in the oryzoid grasses is another distinction 

between the subfamilies. Oryzoids lack an anterior bundle but 

festucoids have an anterior sieve tube attached at the anterior of 

the pistil plexus (Aziz, 1981; Lingle and Chevalier, 1985; 

Pizzolato, 1984, 1987, 1988, 1989a, b). A last readily apparent 
NUMBER 78 7 

distinction between the groups concerns one of the minor 

components, the lodicule traces. Because Leersia lacks a lower 

sieve-element plexus, the lodicule traces merge instead at the 

anterior and flanks of the descending stamen traces (Pizzolato, 

1989b). Most festucoid grasses with lodicules have one trace 

per lodicule with only a phloem component (Pissarek, 1971; 

Pizzolato, 1988, 1989a). Oryza (Pissarek, 1971) and Leersia 

(Pizzolato, 1989b), however, have two traces per lodicule with 

tracheary elements as well as sieve elements. 

Similarities within the Festucoideae and Oryzoideae of Hilu 

and Wright (1982) and the distinctions noted between them are 

a stimulus to continue looking for those characters of the floret 

vascular system that will reveal the natural system of 

classification. Components of the floret vascular system are 

“not intrinsic” to any of the current or older system of 

classification and, thus, should be valuable “external evidence” 

to check and improve the classification systems being 

developed (Macfarlane and Watson, 1982). 

Now that some of the components of the floret vascular 

system are known to distinguish between genera of subfamilies 

unanimously recognized as distinct, a more controversial 

distinction might be attempted. The relative affinities of the 

Oryzoideae and the Bambusoideae are unsettled. Based on a 

synopsis of all readily available characters, Watson et al. (1985) 

and Tucker (1988) consider the Oryzoideae and Bambusoideae 

to be related much more closely to each other than to the 

Festucoideae, whereas, with nearly similar characters, Hilu and 

Wright (1982) consider the Oryzoideae more closely related to 

the Festucoideae than to the Bambusoideae. The Olyreae is a 

tribe of herbaceous Bambusoideae with uniflowered, unisexual 

spikelets (Scderstrom and Ellis, 1987) superficially similar to 

the spikelets in the Oryzoideae and Festucoideae, and, 

therefore, containing genera suitable for comparative anatomical studies. Living specimens of Raddia Bertoloni, 1819, of the 

Olyreae (Soderstrom and Zuloaga, 1985) enabled the continuation of the comparative, descriptive studies of the vascular 

anatomy of grass florets. 

MATERIALS AND METHODS.-During anthesis in midNovember 1988, male and female spikelets with recently 

extruded stamens or stigmas were excised from their inflorescences on specimens of Raddia brasiliensis Bertoloni, 1819, 

originating from Rio de Janeiro, Brazil, and cultivated in the 

Smithsonian Institution Botany Department greenhouse. 

Vouchers prepared by E.J. Judziewicz (his no. 5417) were 

deposited in the United States National Herbarium (US). 

Preparation for microscopy and the construction of a plastic 

facsimile of the vascular system of one male floret and of one 

female floret was accomplished in a way previously detailed by 

Pizzolato (1983, 1988). Each spikelet is oriented in this way in 

the text and figures: anterior (left of page), posterior (right of 

page), right flank (top of page), left flank (bottom of page). The 

clusters of genera, festucoid, oryzoid, and bambusoid, are used 

in the sense of Hilu and Wright (1982) and Soderstrom and 

Ellis (1987). 

ACKNOWLEDGMENTS.-Emmet Judziewicz suggested that 

this study be done and, in a generous and helpful manner, made 

the living specimens of Raddia brasiliensis from the Smithsonian greenhouse available to me for sampling. Eve Luckring 

photographed and printed the pictures of the plastic models. 

Barbara Broge and Karen Engeseth rendered the drawings. Sfin 

Frick translated the study of Butzin (1965). Elaine Eiker typed 

the manuscript, which is published as Miscellaneous Paper No. 

1295 of the Delaware Agricultural Experiment Station. My 

family was a source of encouragement during this study. 

Vascular Morphology of the Male Floret 

The male floret is not visibly subtended by glumes. 

However, subjacent to the base of the floret occurs a node with 

bumps that can be interpreted as one bearing aborted glumes 

(Figure 2, level -25). Above this region, the rachilla of the base 

of the floret contains six vascular bundles, in two rows of three 

on the anterior and posterior of the rachilla (Figure 2, level 5). 

The bundles are small except the middle one of the anterior 

row. At this level on the anterior occurs the lowest part of the 

lemma (Figure 2, level 5), but the lemma is not inserted on the 

rachilla until much higher (Figure 2, levels 185-245). At its 

insertion the lemma is pleated (Figure 2, level 245) so that the 

basal portion forms a pocket (Figure 2, levels 5-245). This 

pocket contained pollen grains. Below the traces to the lemma 

and palea, the six rachilla bundles appear to variously branch 

and merge during their ascent of the rachilla (Figure 2, levels 

5-95). The first traces to become distinct are the lemma median 

and the two laterals (Figure 2, levels 95, 125). Higher, the 

median enters the insertion of the lemma (Figure 2, level 215) 

and continues up (Figure 2, level 245) then down and up the 

pocket formed by the central portion of the lemma (Figure 2, 

from level 245 back to level 35). The extreme lateral portions 

of the lemma, which are entered by the laterals at their 

insertions (Figure 2, levels 185,215), do not descend like the 

middle; thus, the path of each lemma lateral trace is not 

tortuous like the path of the median trace. The two palea traces 

are discrete shortly above the appearance of the lemma traces 

(Figure 2, level 125) and ascend the rachilla to enter the palea 

near the flanks of its insertion on the rachilla (Figure 2, levels 

After the emergence of the lemma and palea traces, a large 

vascular bundle remains in the center of the rachilla or, 

synonymously at this level, the receptacle (Figure 2, levels 

125, 155). The bundle appears to become hollow, then 

dissected, as the traces for the three lodicules and three stamens 

emerge (Figure 2, levels 185-275). Two traces enter each of 

the insertions of the anterior lodicules, but only one trace enters 

the smaller, posterior lodicule (Figure 2, levels 305, 341). 

Three traces remain around the center of the rachilla, and one 

apiece enters each of the three stamen insertions (Figure 2, 

levels 341,380). There is no sign of an aborted pistil where the 

rachilla ends. 

155-341). 
8 SMITHSONIAN CONTRIBUTIONS TO BOTANY 

65 
NUMBER 78 

FIGURE 2 (left).-Tracings of serial transverse sections of the male floret 

arranged acropetally at intelvals indicated in pn (~55). Left and right of page, 

respectively, is anterior and posterior of the floret. Top and bottom of page, 

respectively, is right and left of floret. Closed circular areas within the parts of 

the floret are vascular bundles including their intermediary cells. Level -25 is 

the rachilla below the floret base showing a node bearing the aborted glumes 

fully developed in the female floret of Figure 10. Level 5 is the rachilla at the 

floret base. The large anterior bundle is bundle 3. The posterior, flanking 

bundles are bundle 1 (left) and 2 (right). The segment anterior to the rachilla is 

the lowest part of the lemma. Levels 35 to 275 show that the middle of the 

lemma is a pleated pocket, which bundle 3 traverses after entering between 

levels 275 and 245 after ascending the rachilla from level 5. Bundles 1 and 2 

are, respectively, the left and right laterals of the lemma. The palea traces are 

apparent in the posterior of the rachilla by level 95 but do not occur in the palea 

until between levels 305 and 341. Two traces for each of the anterior lodicules 

and the sole trace for the posterior lodicule appear about level 245. The three 

traces remaining in the center of the rachilla by level 275 are the traces of the 

stamens which are distinct from the rachilla by level 380. 

9 

Vascular Anatomy of the Male Floret 

In the rachilla at the base of the floret about the level of 

Figure 2, level 5, six collateral bundles occur in two rows 

(Figure 3). The tracheary elements in each tend to be nearer the 

center of the rachilla, and the sieve elements are more 

peripheral. Throughout their courses in the rachilla, the 

tracheary and sieve elements tend to be squat and to be 

accompanied by a matrix of intermediary cells. The six bundles 

are small except the large central one of the anterior row. That 

is bundle 3, which probably was initiated first in the rachilla as 

the median trace of the lemma. 

With ascent in the rachilla, the sieve elements from bundle 3 

interconnect with sieve elements from all the other bundles as 

sieve elements horizontally traverse the intervening ground 

parenchyma of the rachilla (Figures 4, 5). This horizontal 

network of sieve elements connecting the phloem of rachilla 

bundles that were isolated at the rachilla base is the lower 

sieve-element plexus. A larger, accompanying horizontal 

system of tracheary elements overlies the lower sieve-element 

plexus (Figure 5). The sieve-element plexus is semicircular and 

open at the posterior because the ground parenchyma between 

rachilla bundles of the posterior row is not bridged by sieve and 

tracheary elements. 

While the sieve and tracheary elements emanating from 

bundle 3 are contributing to the lower sieve-element plexus, 

some elements of bundle 3 ascend to become the median trace 

(M> of the lemma (Figures 4-6). Bundle 3 contributes most of 

FIGURES 3, 4 (right).-Facsimiles of male floret vascular system at levels 

shown in micrometers (flC100). Scale (3 pn in length) remains in parenchyma 

in the same relative position throughout all the levels of the male floret. Figure 

3 identifies the six rachilla bundles at the floret base. Figure 4 shows the lower 

regions of the lower plexus containing most of the horizontally connecting 

sieve elements. (A = anterior of floret; L =left of floret; LL = bundle related to 

lemma extreme left lateral; M = bundle related to lemma median; P =posterior 

of floret; R = right of floret; RR = bundle related to lemma extreme right lateral; 

s = sieve elements; SAU = satellite, supernumerary, superposed, or subsidiary 

bundles associated with bundle 3; t = tracheary elements; 1.2.3 =bundles 1.2, 

3.) 
10 SMITHSON" CONTRIBUTIONS TO BOTANY 

FrOURES 5, 6.-Facsimiles of male floret vascular system at levels shown in micrometers (~700). As sieve and 

tracheary elements from bundle 3 form the lower parts of the lower plexus, sieve and tracheary elements also from 

bundle 3 become the lemma median. The satellite or subsidiary bundles separate from M as they enter the rachilla. 

Besides contributing to the lower plexus in Figure 5. bundles 1 and 2 form the principal lemma laterals. Minor, 

extreme laterals associate with the main laterals. One of the extreme laterals (LL) descends the rachilla without 

merging with its main lateral (L). In Figure 5, columns of tracheary elements flanked by sieve elements ascend 

over M from the right and left of bundle 3 and the lower plexus. In Figure 6, these sieve elements encircle the 

columns of tracheary elements to make the lower layers of the upper plexus. Scale (3 pn in length) remains in 

parenchyma in same relative position throughout all the levels of the male floret. (L = bundle related to lemma 

left lateral, LL = bundle related to lemma extreme left lateral; M = bundle related to lemma median; PL = bundle 

of left of palea; PR = bundle of right of palea; R = bundle related to lemma right lateral; RR = bundle related to 

lemma extreme right lateral, s = sieve elements; SAW = satellite, supernumerary, superposed, or subsidiary 

bundles associated with bundle 3 and M, sl = sieve elements of the left lower parts of the upper sieve-element 

plexus; sr = sieve elements of the right lower parts of the upper sieve-element plexus; t = tracheary elements; tl 

= column of tracheary elements associated with the left lower palts of the upper sieve-element plexus; tr = 

columns of tracheary elements associated with the right lower parts of the upper sieve-element plexus; 1,2, 3 = 

bundles 1.2,3.) 

the vascular tissue of M. However, bundle 3 is a composite 

bundle consisting of the vascular tissue of bundle 3 accompanied by two flanking components, which in farther descending 

the rachilla become the smaller bundles in the anterior row of 

bundles at the floret base (Figures 6-3). Probably, these 

satellite bundles of M were initiated higher and later in the 

rachilla than bundle 3. Before descending the rachilla, the 

satellites also participate in the lower plexus (Figures 5,4). 

Also participating in the lower plexus are the flanking 

bundles from the posterior row of the rachilla (Figures 3-5). 

These are bundles 1 and 2. Like bundle 3, they probably were 

initiated isolated in the rachilla near the site of the lower 

sieve-element plexus and differentiated basipetally in the 

rachilla and acropetally into the lemma. Above the lower 

plexus, bundles 1 and 2 become the lemma laterals (Figures 5, 

6). 
NUMBER 78 11 

FIGURES 7-9.-Facsimiles of the upper portions of the upper plexus of the 

male floret at levels shown in micrometers (~7cIoo). In Figure 7, the columns 

of tracheary elements from the lower upper plexus of Figure 6 become 

horizoatally interconnected in the center of the plexus as the sieve elements 

interconnect around them. In Figure 8, the central region of parenchyma in the 

upper plexus becanes larger as podons of the plexus cluster under the 

influence of the traces of the anterior lodicules and the stamens. In Figure 9. the 

lodicule traces enter the upper plexus between the clusters related to the stamen 

traces. The posterior lodicule trace connects to the upper plexus in the gap 

between the clusters dated to the right and left stamen traces. Tracheary 

elements of the inner traces of the right and left lodicule (t with dot) can be 

followed throughout the upper plexus (Figures 6-9). Scale (3 tun in length) 

remains in parenchyma in same relative position throughout all the levels of the 

male floret, (AS = anterior stamen trace; LS =left stamen trace; LID = the two 

traces of the left lodicule; PLO = trace of the posterior lodicule; RLO = the two 

traces of the right lodicule; RS = right stamen trace; s = sieve elements; t = 

tracheary elements.) 

Only two laterals ascend the lemma (Figure 2). However, in 

the rachilla in the vicinity of the lower sieve-element plexus, a 

smaller, inner bundle unites with each lateral before it ascends 

the lemma (LL and RR in Figures 5, 6). These poorly 

developed extreme laterals were probably initiated higher in the 

rachilla than the larger laterals and had a short acropetal course. 

The small, right, extreme lateral had a brief descent in the 

rachilla before merger with its larger partner; however, the 

small, left, extreme lateral missed fusing with its larger partner 

and descended far in the rachilla (Figures 5-3; Figure 2, level 

5). Therefore, one should expect variation at the rachilla of the 

floret base in the bundle number due to the presence or absence 

of mergers of the satellites of bundles 1,2, and 3. 

The two palea traces were probably initiated higher and later 

in the rachilla than bundles 1,2, and 3. In descending from the 

palea, the left trace of the palea (PL) merges where it is 

obstructed by bundle 1, which is proliferating to contribute to 

the lower sieve-element plexus (Figures 6, 5). In its descent 

from the palea, the right trace (PR) behaves like the left in 

merging with proliferating bundle 2 at the lower sieve-element 

plexus. 

Sieve and tracheary elements rise from the center of the 

lower sieve-element plexus to form the lower portion of the 

upper sieve-element plexus and accompanying tracheary 

elements (Figures 5,6). Bundle 3 contributes most of the sieve 

and tracheary elements to the lower levels of the upper plexus. 

The center of the lower plexus from which the upper plexus 

emanates is a triradiate ridge of tracheary elements around 

whose radii the sieve elements flow upward (Figure 5, note sr 

and sl). The tracheary elements accompanying the ascending 

sieve elements rise from each of the radii in three columns 

(Figure 5, note tr and tl). The two columns of tracheary 

elements that are more to the right and the accompanying sieve 

elements form the right leg of the upper plexus (Figure 5, note 

tr and sr), and the left column forms the left leg of the upper 

plexus (Figure 5, note tl and sl). The sieve elements of the 

plexus then cross horizontally among the three columns as well 

as around the whole unit, creating the lower levels of the upper 

sieve-element plexus (Figures 5, 6). As the sieve elements 

create the encircling pattern of the upper sieve-element plexus, 

within it the columns of tracheary elements become horizontally interconnected (Figures 6,7). The uppermost levels of the 

upper sieve-element plexus with accompanying tracheary 

elements resemble two concentric circles-an outer system of 

horizontal sieve elements and an inner system of horizontal 

tracheary elements-surrounding ground parenchyma devoid 

of conducting cells (Figures 7, 8). Probably the upper 

sieve-element plexus and accompanying tracheary elements 
12 SMITHSONIAN CONTRJBUTIONS TO BOTANY 

developed from a residual meristem persisting in the rachilla 

between bundle 3 and the insertions of stamens and lodicules. 

The uppermost portions of the upper sieveelement plexus 

and accompanying tracheary elements are the levels of merger 

of the lodicule traces and stamen traces (Figures 8,9). The five 

collateral traces from the three lodicules enter the upper plexus 

lower and more diagonally than the three collateral traces from 

the three stamens. The patterns of the sieve and tracheary 

elements of the upper plexus as they are directed toward the 

stamen and anterior lodicule traces-despite the interconnwtions just emphasized--reflect the influence of these traces on 

the formation of the upper plexus. The pattern, in which the 

anterior of the upper sieve-element plexus and accompanying 

tracheary elements emanate from the lower plexus, supplies the 

anterior stamen trace and the flanking trace pairs of the anterior 

lodicules (Figures 5-8). The vascular pattern of the posterolateral portions of the upper plexus serves the posterior stamens 

(Figures 5-8). The posterior lodicule trace, which appears to 

have influenced the pattern of the upper plexus least joins it at 

horizontal connections below the gap between the posterior 

stamen traces (Figures 9-7). 

Therefore, the upper sieveelement plexus and accompanying tracheary elements axially link the lower plexus and the 

traces of the lodicules and stamens. Although the upper plexus 

is a horizontally interconnected vascular system, it consists of 

axial components formed from a residual meristem, under the 

acrofugal influence of the traces of the anterior lodicules and of 

the stamens, and under the basifugal influence of bundle 3. 

Vascular Morphology of the Female Floret 

The female floret, which is larger in most aspects than the 

male, is subtended by two large, vascularized glumes (Figure 

10, level 1). The rachilla of the base of the floret contains an 

anterior vascular bundle and two flanking, but somewhat, 

posterior bundles. The three bundles are surrounded by ground 

tissue of sclerified parenchyma, in contrast with the thin-walled 

parenchyma in the same region of the male floret; with ascent, 

the rachilla parenchyma becomes thin-walled. The three 

bundles become larger and variously joined and dissected as 

they ascend the rachilla (Figure 10, levels 21-131). At the 

same levels near the lemma insertion, the lemma median and 

paired lemma laterals become discrete from the vascular 

system in the rachilla (Figure 10, levels 131-220). The central 

portion of the female lemma does not form a pleated anterior 

pocket as does the male lemma. From the Same regions of the 

mchilla as the apparent emergences of each of the pairs of 

lemma laterals, the palea traces emerge (Figure 10, levels 

131-161). However, they reach the palea more distally on the 

mchilla (Figure 10, levels 191-428). 

Above the emergences of the palea traces, the rachilla is 

filled with a large bundle, from whose anterior flanks three 

traces emerge toward the anterior lodicule insertions (Figure 

10, levels 250-398). The posterior lodicule insertion contains 

one trace (Figure 10, levels 428, 458) that emerges about the 

same levels as the traces of the anterior lodicules (Figure 10, 

levels 250,280). Alternating with the lodicule insertions, three 

avascular, aborted stamens emerge from the rachilla or 

receptacle and ascend 100 pm (Figure 10, levels 428-607). 

The large bundle remaining in the rachilla or receptacle above 

the emergence of the lodicule traces is the lowest vascular 

tissue related to the pistil (Figure 10, levels 339-398), which is 

lacking in the male floret. 

A vascular bundle merges at each flank of the vasculature of 

the base of the pistil (Figure 10, level 428), shortly below the 

locule, which is in the anterior of the ovary (Figure 10, level 

518). Each bundle probably descended from a stigma, through 

a long style (Figure 11, levels 1152, 1112), and through the 

right and left flanks of the ovary (Figure 11, levels 1072-752; 

Figure 10, levels 518-428) before the merger. These stylar 

bundles are called “posterolateral bundles” to distinguish them 

from an anterior bundle that probably does not occur in any 

species of Raddia. 

The large vascular bundle in the posterior of the ovary 

behind the locule is the placental bundle (Figure 10, levels 

518-712). Proximally, the placental bundle merges with the 

vasculature of the pistil base (Figure 10, levels 518-428). 

Distally, the placental bundle supplies the ovule. 

The ovule fills the locule but is free from the interior ovary 

wall except at the placenta. The placenta is the region of merger 

of one or both integuments of the ovule with the interior 

posterior wall of the ovary. Figure 10, level 547 is the lowest 

level of the placenta. The placenta ends between levels 992 and 

1032 of Figure 11. The chalaza is that part of the ovule where 

the epidermises of the integuments and of the nucellus are not 

interposed between the internal posterior of the ovary and the 

FIGURE 10.-Tracings of serial transverse sections of the female floret arranged 

acropetally at intervals indicated in pn (~55). Left and right of page, 

respectively, is anterior and posterior of the floret. Top and bottom of page, 

respectively, is right and left of the floret. Closed circular areas within the parts 

of the floret are vascular bundles including their intermediary cells. Level 1 is 

the floret base with the inner and outer glumes surrounding the rachilla 

containing bundles 3, 2, and 1. Bundle 3 is the more anterior one. Bundle 1 is 

at the rachilla left, and bundle 2 is at the right. Glumes are not drawn higher. In 

levels 131-191, the lemma median trace becomes distinct from bundle 3. The 

paired left and right laterals of the lemma become distinct from bundles 1 and 

2, respectively. Also, the traces of the left and right of the palea become distinct 

from the lemma laterals. By level 309, the lemma is distinct from the anterior 

of the rachilla. and the three traces of each of the pair of anterior lcdicules are 

distinct as is that of the posterior lodicule. By levels 458 and 488, the palea, 

three lodicules, and three stamincdia are distinct from the rachilla. Lemma and 

palea are not drawn higher. By these levels, the posterolateral (stylar) bundles 

are fusing with the rachilla bundle related to the pistil. This fusion occurs below 

the level of the locule shown by the dashed circular areas of levels 518 and 

higher, the ovule fiis the locule. The large bundle in the pistil posterior of 

levels 518-577 is the placental bundle. By level 607, as the tips of the 

staminodia are reached, the placental bundle joins the nucellus of the ovule 

forming the base of the chalaza. The solid line is the posterior of the placental 

bundle and the dashed line is the boundary between the inner ovary wall and the 

outer walls of the integuments. 
NUMBER 78 13 
14 SMITHSONUN CONTRIBUTIONS TO BOTANY 

FIGURE 1 l.-Continuatim of the floret in Figure 10 (65). The right and left 

posterolaterals flank the ovule and continue beyond it into the style. From 

levels 752 to 992 the locule and ovule are shown by the dashed outer line (the 

boundary between the inner ovary wall and outer walls of the integuments) and 

a solid line (the posterior of the placental bundle). At levels 952 to 1032, the 

inner boundaries of the smaller, outer integument and of the larger, inner 

integument now are shown by the dashed lines enclosed by the dashed 

boundary between the inner ovary wall and the outer wall of the integuments 

previously indicated. By level 992, the chalaza ends as the nucellar epidermis 

(dashed circle) interposes between the nucellus and the placental bundle (solid 

line of ovule). By level 1032, the tip of the ovule is only the inner and outer 

integument filling the locule. The placental bundle no longer joins the ovule but 

is posterior to the ovule. By level 1072, the locule is passed and superseded by 

the stylar core (the large circle). The placental bundle contacts the posterior of 

the stylar core. By level 11 12, the placental bundle ended and the stylar core 

ascends the style. Lemma and most of the palea are included with the tracing of 

the style in level 1152. 

internal tissues of the nucellus. That is, the chalaza occurs 

where the nucellus and ovary wall are merged. The lowest level 

of the chalaza is between levels 577 and 607 of Figure 10; the 

highest level is between levels 952 and 992 of Figure 11. The 

placental bundle fills most of the placenta. 

The placental bundle extends higher than the placenta 

(Figure 11, level 1032). The placental bundle fades out in 

contact with an avascular, parenchymatous cylinder of the style 

which supersedes the ovule and locule (Figure 11, levels 1072, 

1112). This stylar core continues up the style, flanked by the 

posterolateral bundles. 

Vascular Anatomy of the Female Floret 

One anterior and two flanking posterior collateral bundles of 

large area occur in the rachilla at the floret base (Figure 12). 

Throughout their courses in the rachilla, the cytology of the 

tracheary elements, sieve elements, and intermediary cells from 

these bundles resembles their cytology in the male floret. The 

centripetal placement of the xylem of these bundles and their 

sequent courses in the rachilla and lemma indicate that the 

anterior bundle is the homologue of bundle 3 and that the 

posteriors are the homologues of bundles 1 and 2 in the male 

rachilla. 

With ascent in the rachilla, bundles 3, 2, and 1 make the 

lower sieve-element plexus and accompanying tracheary 

elements. Most of the sieve and tracheary elements emanate 

from bundle 3. As the sieve elements ascend diagonally from a 

widening bundle 3 (Figures 12, 13) they form a V (Figures 14, 

15). Tracheary elements emanating from those of bundle 3 

accompany both sides of each phloic arm of the V (Figures 14, 

15). The tips of the arms of the V then bend horizontally toward 

the flanks of the rachilla. Thus, bundle 3 forms wings of 

horizontal sieve elements sandwiched by the accompanying 

tracheary elements (Figures 15, 16). Merger of these derivatives of bundle 3 with a similar arrangement of sieve and 

tracheary elements from bundles 1 and 2 completes the 

semicircular lower sieveelement plexus and accompanying 

tracheary elements (Figure 16). Probably as occurs in the male 
NUMBER 78 15 

FIGURE 12.-Facsimile of female floret vascular system at 1-3 pn above the 

base of the floret (~700). Note the three bundles in the rachilla at the floret base. 

Arrows indicate that while ascending to Figure 13, tracheary elements of 

bundles 1 and 2 spread centrifugally and posteriorly but tracheary elements of 

bundle 3 spread centrifugally and laterally. As sieve elements from bundles 1 

and 2 ascend between Figures 12 and 13. they envelop the xylem except at the 

interior of the rachilla. The sieve elements of bundle 3 spread laterally without 

enveloping the xylem. Scale (3 pn in length) remains in parenchyma in the 

same relative position throughout all the levels of the female floret. (A = 

anterior of floret; L = left of floret; P = posterior of floret; R = right of floret; 

s = sieve elements; t = tracheary elements; 1.2.3 = bundles 1,2,3.) 

floret at this level, the lower sieve-element plexus arises as 

vascular shunts between bundle 3 and bundles 1 and 2. The 

view of the upper levels of the sieve-element plexus of the 

female floret shown in Figure 16 corresponds to the level of the 

male floret in Figure 5. 

As in the male floret, the second role of bundle 3 is as median 

trace for the lemma (M). Bundle 3 becomes M in two levels. A 

few tracheary elements continuous with those from the lemma 

median connect at a low level to the inner xylem of both arms 

of the V of bundle 3 (Figure 15). Near this level, all of the sieve 

elements from the lemma median connect to the sieve elements 

in the crotch of the V of bundle 3 (paired stars in Figures 

16-14). The higher level of connection between bundle 3 and 

M involves only the tracheary elements. These have a thick, 

broad, horizontal course from M through the gap of intermediary cells between the ascending arms of the V of bundle 3 

(Figures 17, 16). After passing horizontally through the gap of 

the V, the tracheary elements from M then descend vertically to 

end in intermediary cells in the posterior of bundle 3 (single 

stars in Figures 16-14). 

Thus, there were probably two sites of initiation, which 

merged in development, for the creation of the lemma median 

trace: a lower one in the rachilla initiating bundle 3, and a 

superposed one nearer the insertion of the lemma that produced 

most of the xylem. There is likelihood that the two satellite 

bundles in the lemma median of the male floret, which consist 

largely of tracheary elements (Figures 5, 6), are moieties 

homologous to the superposed xylem bundle of the lemma 

median of the female floret. Because the center of the male 

rachilla, but not of the female, was obstructed by the 

developing lower sieve-element plexus and accompanying 

xylem, the developing satellite bundles of the male, unable to 

merge over bundle 3 and descend behind it, split around the 

rachilla (Figure 5). 

Just as bundle 3 of the female floret contributes to the lower 

sieve-element plexus as well as to the lemma median, so do 

bundles 1 and 2 contribute to the lemma laterals, besides their 

roles in the formation of the lower sieve-element plexus. 

Bundle 1 forms in the rachilla as the trace for one of the left 

laterals (L or LL) of the lemma, and bundle 2 forms as the trace 

for one of the right laterals (R or RR; Figures 12-14). Because 

the mergers of the right and left laterals with their respective 

rachilla bundles are nearly equal, one cannot determine which 

of each lateral pair was the original bundle in the right and left 

of the rachilla (Figure 15). Using the male floret as a guide 

(Figure 6) suggests that the laterals closer to the median 

originated in the rachilla as bundles 1 and 2. The palea traces of 

the female floret behave the same as in the male floret, for each 

trace descends from the palea to merge, respectively, with 

bundles 1 or 2 as they proliferate in contributing to the lower 

sieve-element plexus and accompanying xylem (Figures 6, 15, 

16). 

From the semicircular, lower sieve-element plexus and 

accompanying xylem (Figure 16), the upper sieve-element 

plexus and its xylem rise uniformly (Figure 17). In the male 

floret, the formation of the upper plexus is influenced by the 

traces from the insertions of the anterior lodicules and stamens. 

Because the aborted stamens do not initiate traces, the anterior 

lodicules are the predominant influence on the shape of the 

upper plexus of the female floret. Accordingly, the posterior of 

the upper plexus remains open due to the absence of any 

influence from the posterior stamens (Figures 17, 18). At its 

middle levels, the upper sieve-element plexus and accompanying xylem consist of two opposed arcs open to the wide gap, 
16 SMITHSONIAN CONTRIBUTIONS TO BOTANY 
NUMBER 78 17 

FIGURE 13.-Facsimile of female floret vascular system at 3-55 pn above the 

base of the floret (x1ooO). Arrows indicate the path of ascent of tracheary and 

sieve elements of bundles 1, 2, 3 to Figure 14. The position of the numbers 

identifying the bundles is in the same relative position in Figures 12 and 13 

indicating that the tracheary elements do not rise centripetally. Stars are in a 

region of intermediary cells centripetal to bundle 3 below tracheary elements 

descending from Figure 16 through Figure 14. Scale (3 pn in length) remains 

in parenchyma in the same relative position throughout all the levels of the 

floret. (s = sieve elements; t = tracheary elements; 1,2,3 = bundles 1, 2, 3.) 

which is over the superposed tracheary elements to M and 

which is continuous with the gap of the open posterior (Figure 

17). At its middle levels, the anterior gap in the upper plexus 

persists over M because the anterior stamen trace is lacking. At 

the highest levels of the upper plexus, the anterior gap over M 

is bridged by horizontally shunting tracheary and sieve 

elements from the arcs (paired dots in Figure 18). The shape of 

each arc is influenced by the two peneposterior, collateral traces 

of the anterior lodicules (PEP) of the left and right (Figures 18, 

17). The anterior trace from each of the anterior lodicules 

(Figure 18) appears to have joined the upper sieve-element 

plexus and accompanying xylem after its bi-arcuate shape was 

determined by the two major traces from each anterior lodicule. 

Two massive lobes basipetally merge with the rest of the 

vascular system filling the posterior gap of the upper and lower 

plexi (Figures 18-16). These two broad prongs or lobes (POP) 

merge with the posterior of the open lower plexus (Figures 17, 

16) after descending through the rachilla from the pistil plexus 

in the base of the pistil (Figure 10, level 398; Figure 20). 

During their basipetal course from the pistil plexus to the lower 

plexus, these lobes complement the bi-arcuate upper plexus to 

form a massive, hollow cylinder over the trace to the lemma 

median (Figure 18). The posterior of the right lobe from the 

pistil plexus is the site of merger of the solitary collateral trace 

from the posterior lodicule (Figure 18). Probably, there is 

variation among female florets in the linkage of this minor trace 

to the right or left lobe from the pistil plexus. 

The pistil plexus, which sends down these lobes, is a large 

disk of tracheary elements virtually encircled by sieve elements 

in the rachilla (receptacle) at the pistil base (Figure 10, levels 

368, 398; Figure 20). The pistil plexus sends down centrifugally three interconnected pairs of vascular prongs into the 

rachilla (AP, RPP, LPP in Figure 19). The anterior pair is of 

small, collateral bundles (AP in Figure 19), which soon merge 

with the anterior, horizontally shunting, tracheary and sieve 

elements of the upper plexus (Figure 18). The other two pairs 

of prongs descending from the pistil plexus are larger, less 

discrete, and more nearly amphivasal than the anterior pair 

(Figure 19). Each of the more posterior pairs continues 

descending the rachilla centrifugally (Figure 18) while merging 

to become the broad lobes that fuse anteriorly with the upper 

plexus to close the posterior gap of the lower plexus (Figures 

17, 16). 

The complex arrangement of the sieve and uacheary 

elements in these vascular components developing from the 

pistil plexus beggars description. The pistil plexus is a vast 

reticulum of tracheary elements almost encircled by an 

enveloping reticulum of sieve elements (Figure 20). The two 

pairs of interconnected vascular prongs that descend from the 

pistil plexus to form the broad posterior lobes do so in a curious 

way. Segments descend from the sieve-element rim of the pistil 

plexus (darts in Figures 20, 19). Tracheary elements from the 

center of the pistil plexus penetrate cenaifugally around the 

descending sieve elements and become interconnected on all 

sides of these clusters of sieve elements (Figures 19,18). These 

events, which occur more precipitously at some sites than in 

others during the descent from the pistil plexus, eventually 

cause the right and left prong pairs to become the lobes. As the 

clusters of sieve elements in the lobes begin to become isolated 

by the encircling tracheary elements, the sieve elements from 

adjacent clusters reconnect within the encasing tracheary 

elements of a lobe (Figure 18). In this way, the descending 

lobes from the virtually amphicribral pistil plexus are an 

amphivasal weave of sieve and tracheary elements merging 

anteriorly with the upper plexus (Figure 17) and posteriorly 

with the lower plexus (Figure 16). 

Now that the basipetal attachments of the pistil plexus to the 

upper and lower plexi in the rachilla are described, the two 

portions of the pistil vasculature attached at the upper pistil 

plexus can be detailed. First, the stylar or posterolateral, 

collateral bundles merge with the flanks of the pistil plexus 

(RPL and LPL in Figure 20), which occurs far below the ovule 

and the placental bundle (Figure 10, level 428). Second, the 

placental bundle emerges, without fanning out, above the 

posterior of the contracting pistil plexus (Figures 21,22). The 

rim of sieve elements contracts by closing upon a small core of 

sieve elements-which is continuous with the rim-within the 

enclosed reticulum of tracheary elements (paired dots in 

Figures 20, 21). Since sieve and tracheary elements do not 

continue rising from the anterior of the contracting pistil 

plexus, the placental bundle becomes an arc of sieve elements 

opening toward the ovule and embracing the uacheary 

elements (Figure 22). Mature tracheary and sieve elements 

diminish and then end in immature elements in the placental 

bundle before it attains the level of the placenta (Figure 10, 

level 518). At the time of sampling, immature elements had 

developed into the placenta but not into the chalaza (Figure 10, 

level 577). Intermediary cells, which have accompanied the 

sieve and tracheary elements throughout their courses, continue 

the placental bundle beyond the placenta (Figure 11, level 

1032), above the ovule into the base of the style. There the 

bundle ends after contacting the stylar core (Figure 11, levels 

1072, 1112). 

Figure 23 summarizes the basic pattern of the components of 

the male and female florets but neglects the subtleties of the 

system emphasized in the preceding descriptions of the 

facsimiles. Figure 23 emphasizes the similarities of the 

vasculature of the florets. Differences in the components of 

male and female florets are explained largely (1) by the absence 
18 SMITHSONUN CONTRIBUTIONS TO BOTANY 
NUMBER 78 19 

F~~URE 14.-Facsimile of female floret vascular system at 55-101 pm above 

the floret base (x1OOO). Position of numbers identifying bundles 1,2,3 are in 

same relative positions of Figure 13. Stars by tracheary elements show those 

descending into intermediary cells of the posterior of bundle 3 fm Figure 16. 

Arrows indicate where regions of bundles 1.2.3 ascend to cmtinue into Figure 

15. Bundle 3 is at the level where it resembles the base of a V. No tracheary 

elements rise from those between the brackets, although tracheary elements and 

sieve elements ascend from outside the brackets. Paired stars indicate the 

attachment of the sieve elements so marked in Figure 15. Scale (3 pn in length) 

remains in parenchyma in the same relative position through all the levels of the 

floret. (L = lemma left lateral trace; LL = lemma extreme left lateral trace; PL 

=left trace of palea; PR = right trace of palea; R =lemma right lateral trace; RR 

=lemma extreme right lateral trace; s = sieve elements; t = tracheary elements; 

1,2,3 =bundles 1,2,3.] 

~ ~ ~~~~~~~~ 

of gynoecial components compensated by an enhanced 

(relative to festucoid and oryzoid grasses) role of the lodicule 

components in the male floret, and (2) by elaborated gynoecial 

components compensating the loss of the androecial components in the female. 

Comparative and Phylogenetic Considerations 

COMPONENTS OF THE FLORET VASCULAR 

SYSTEM OF Ruddia ARE COMPARED TO THOSE 

KNOWN IN THE FESTUCOIDEAE AND ORYZOIDEAE 

The large anterior bundle in the rachilla at the base of both 

florets is the origin of the lemma median in Ruddia and in all 

other investigated festucoid and oryzoid grasses (Pizzolato, 

1989a, b). This bundle is designated bundle 3, and in Ruddia 

and in most festucoid grasses, but not in oryzoid grasses, the 

xylem occurs between the phloem and the lemma (Figures 3, 

12; Table 1, row 2). Besides bundle 3, several other bundles are 

in the rachilla at the floret base of Raddia and of most festucoid 

grasses (Table 1, row 1). These bundles are the origins of the 

lemma laterals and palea traces. Some of these bundles are 

actually composite bundles: the posterior ones of Phalaris and 

Phleum combine, respectively, the palea traces and the lemma 

extreme lateral traces (Pizzolato, 1988, 1989a); bundles 1 and 

2 of the female floret of Raddia are composites of both lemma 

laterals on their respective sides. 

The ground tissue of the rachilla surrounding the bundles of 

the floret base is usually of parenchyma, and in Raddia it is a 

particularly sclerified matrix for the thinly walled tissues of 

bundles 3, 2, and 1 of the female floret (Figure 10, level 21). 

This may create a brittle condition in the rachilla favorable to 

the violent dispersal of the mature female floret commented 

upon by Davidse (1987). Arber (1929) also mentions the 

extreme sclerification of the parenchyma around the bundles at 

the lemma and palea insertions of the olyroid ally, Streptochaeta Schrader ex Nees, 1829. 

Pizzolato (1987, 1989a) has considered developmental 

explanations for the varying number of rachilla bundles at the 

base of the floret. He concluded that, in aggregate with other 

influences, rachilla amplitude increases rachilla bundle number. His conclusion cannot be totally correct because the 

smaller rachilla at the base of the male floret of Raddia contains 

twice as many bundles as does the big rachilla of the female 

floret (Figure 2, level 5; Figure 10, level 21). 

After originating in the floret base as the traces for the lemma 

and palea, the rachilla bundles in most of the festucoid grasses 

and in Raddia become interconnected into the lower plexus 

(Figures 4, 5, 14-16; Table 1, row 4). In these genera, bundle 

3 contributes most of the vascular tissue to the lower plexus. 

The lower plexi of both Ruddia florets differ from those of the 

festucoid grasses, which are closed on the posterior. The lower 

plexi of the Raddia florets are open at the posterior because 

bundles 1 and 2 are farther apart with no intervening bundles 

(Figures 13, 14) or with only a descending small branch from 

bundle 1 (Figures 3, 4). Sieve elements dominate the lower 

plexi of the festucoid grasses except Anthoxanthum (Pizzolato, 

1987, 1988, 1989a). In Anthoxunthum (Pizzolato, 1984) and 

Raddia, the lower sieve-element plexus is accompanied by a 

large volume of tracheary elements. 

Besides contributing the most to the lower plexus, rachilla 

bundle 3 originates and serves as the lemma median in Raddia. 

Bundle 3 behaves so in all the non-panicoid genera studied 

("able 1, row 2). However, Raddia differs markedly from these 

genera because it has multiple sites of origin in the rachilla. One 

is in the normal position in the rachilla (Figures 4, 5, 13, 14) 

and the other, smaller, sites are higher and nearer the lemma 

insertion (Figures 5, 16, 17). These satellite or supernumerary 

or superposed bundles of the median have only a brief 

horizontal course before merging with M distally and bundle 3 

proximally. Thus, these superposed bundles of the lemma 

median were unnoticed until now (Table 1, row 3). However, 

Page (1947) noted them in the midribs of vegetative leaves of 

most of the genera of the Olyreae including Raddia and in 

midribs of olyroid allies such as Streptochueta. Her findings in 

leaves were confirmed and extended by Metcalfe (1960), 

Calder6n and Soderstrom (1973), and Renvoize (1985). Some 

of the variation in number and position of the satellites of 

midribs noted by Page (1947) and Metcalfe (1960) is similar to 

the variation in the positions of the superposed bundles relative 

to bundle 3 that occurs between the male and female floret 

lemma median of Raddia. The discovery of superposed bundles 

in the rachilla at the lemma median of Raddia supports the 

conclusions of Barnard (1957) and Sharman (1960a, b), from 

their developmental studies, that vegetative leaves and lemmas 

are homologous in all grasses including the bamboos. 

Apparently, the median trace of all bamboo leaves has multiple, 

isolated sites of procambial initiation in the rachilla near the 

insertion in contrast to the one isolated site of initiation of 

festucoid grasses (Hitch and Sharman, 1968; Patrick, 1972; 

Pizzolato and Robinson-Beers, 1987). 

Of the investigated genera, Ruddia is most like the festucoid 

genera in its producing an upper plexus ("able 1, row 8). The 

upper plexi of the festucoid grasses is different, however, 

because in them the stamen traces are the principal influence on 
20 SMITHSONIAN CONTRIBUTIONS TO BOTANY 
NUMBER 78 21 

ROURE 15.-Facsimile of female floret vascular system at 101-119 p above 

the floret base (~700). Figures 14 and 15 show the lowest levels of the lower 

plexus. Positions of numbers identifying bundles 1, 2, 3 are in same relative 

positions of Figure 13. Stars by tracheary elements show those descending into 

intermediary cells of the posterior of bundle 3 from Figure 16. Bundle 3 is at the 

level where its phloem and xylem arms are rising from the base of the V shown 

in Figure 14. No tracheary elements rise from the crotch of the V (the 

out-of-focus view of Figure 14). Paired stars mark the attachment of the sieve 

elements from M so marked in Figure 14. The arms of the V of bundle 3 

between the brackets flow into the parts of the lower plexus so marked in Figure 

16. The tracheary and sieve elements from bundles 1 and 2 with paired dots 

mnnect at the regions of the lower plexus so marked in Figure 16. Scale (3 p 

in length) remains in parenchyma in the same relative position throughout all 

the levels of the floret. (L = lemma left lateral trace; LL = lemma extreme left 

lateral trace; PL = left trace of palea; PR = right trace of palea; R = lemma right 

lateral trace; RR = lemma extreme right lateral trace; s = sieve elements; t = 

tracheary elements; 1,2,3 = bundles 1,2,3.) 

the form of the plexus. In the male floret of Raddia, the 

influence of the three stamen traces is shared with the traces 

from the anterior lodicules. In the female floret of Raddia, the 

peneposterior traces from the anterior lodicules determine the 

form of the upper plexus. That is why the upper plexus is 

circular, not lobed, in the male floret (Figures 6-9) of Raddia, 

but is bi-arcuate in the female floret (Figures 17, 18). The trace 

of the posterior lodicule acts like a minor vein by not 

influencing the form of the upper plexi. 

Of all the genera investigated three dimensionally, only 

Raddia has a posterior lodicule. Oryzoid lodicules are similar 

to those of Raddiu because their traces contain tracheary and 

sieve elements, not just sieve elements as do the festucoid 

grasses (Table 1, row 7). The traces from the oryzoid lodicules 

and stamens are like that of the posterior lodicule of Raddia 

TABU 1.4omponents of the floret vascular system useful in characterizing the Oryzoideae, Olyreae, and 

Festucoideae. 

Components 

1. Rachilla bundles at floret base 

2. Rachilla bundle for lemma median 

3. Rachilla bundle for lemma median with satellites 

4. hwer plexus 

5. Paleatraces 

6. Vascularized posterior lodicule 

7. Traces in lodicules 

8. Uprplexus 

9. Anterior lodicule traces and the vascular system 

10. Stamen traces and the vascular system 

11. Pistil plexus prongs to lower components 

12. Anterior bundle 

13. Posterolaterals 

14. Posterolateral attachment 

15. Placental bundle maturity at anthesis 

16. Placental bundle continues above ovule 

17. Xylem discontinuity 

* except Alopecwus 

t except Anthoxanthwn 

Sources: 

Ory zoideae Olyreae Festucoideae 

one few few* 

collateral, collateral, collateral*, 

parallel tissues perpendicular tissues perpendicular tissues 

no Yes no 

no Yes yes* 

median, laterals laterals*t 

laterals 

no Yes no 

tracheary, tracheary, sieve elements 

sieve elements sieve elements 

no Yes Yes 

autonomous integral autonomous 

autonomous integral integral 

one, few, few, 

autonomous integral integral 

no no Yes 

tracheary, tracheary, sieve elements 

sieve elements sieve elements 

gynobasic. gynobasic, high, 

at pistil plexus at pistil plexus at placental bundle 

tardy prompt 

no Yes no 

no no Yes 

Olyzoideae data based specifically on Leersiu virginicu (Pizzolato, 1989b). 

Olyreae data based specifically on Ruddiu brusiliemis. 

Festucoideae data based spedfically on Alopecwus curoliniunw (Pimlato, 1987), Anthoxanthwn odorutwn (Pizzolato, 1984), Phuluris 

urlurdinuceu (Pizzolato, 1989a), Phlewnprutenre @mlato, 1988). and Trificwn uestivum (O’Brien et al., 1985). 
22 SMITHSONIAN CONTRIBUTIONS TO BOTANY 

FIGURE 16.-Facsimile of female floret vascular system at 119-164 pm above the floret base showing the upper 

levels of the lower plexus (~500). After the tracheary elements of M pass through the gap of the crotch of the V 

of bundle 3 shown in Figure 15, they descend into the posterior of bundle 3 shown by stars. There are a few 

cmtacts of the peripheral tracheary elements of M with the trachealy elements of the inside of the arms of the V 

from bundle 3. Sieve elements from M contact sieve elements of the V at the paired stars. Regions of the lower 

plexus marked by brackets and paired dots show mergers with the areas similarly shown in Figure 15. The regions 

between the arrows are the lowest levels of the pistil plexus fiiing the posterior gap of the lower plexus. Scale (3 

pn in length) remains in parenchyma in the same relative position throughout all the levels of the floret. (M = 

lemma median trace including its superposed satellite bundle; PL = left trace of palea; PR = right trace of palea; 

s = sieve elements; t = tracheav elements.) 

because these traces appear as minor traces by not influencing 

the formation of an upper plexus (Figures 8,9, 18). 

All the studied genera produce a pistil plexus at the base of 

the pistil from which descends one or more vascular prongs that 

connect to the lower components in the rachilla. The pistil 

plexus of the female floret of Raddia behaves like that of 

festucoid grasses by sending down multiple prongs to connect 

intimately with the lower components (Table 1, row 11). In the 

festucoid genera, the prongs from the pistil plexus merge with 

the upper plexus, which obstructs further descent (Pizzolato, 

1984, 1987, 1988, 1989a). However, the female upper plexus 

of Raddia opens at the posterior. Therefore, the prongs from the 

pistil plexus of Raddia not only merge on the anterior with the 

upper plexus (Figures 19,18) but also on the posterior with the 

lower plexus (Figures 17, 16). 

Although all festucoid grasses have an anterior bundle that 

attaches at the pistil plexus (Table 1, row 12), neither Raddia 

nor Leersia (Pizzolato, 1989b) has one. Raddia and Leersia are 

similar also in that the posterolaterals (stylar bundles) contain 

tracheary and sieve elements that merge with the pistil plexus 

below the ovule (Figure 20), not with the placental bundle at 

the level of the ovule typical of the festucoid grasses (Table 1, 

rows 13, 14). 

The placental bundle emerges from the posterior of the pistil 

plexus in all grasses studied. The placental bundle of Raddia 

and Leersia is somewhat less mature by anthesis than that of 
NUMBER 78 23 

FrGURE 17.-Facsimile of female floret vascular system at 164-214 pm above the floret base showing the middle 

levels of the uppr plexus and posterior prongs from pistil plexus (goo). Scale (3 pm long) remains in 

parenchyma in the same relative position throughout all of the levels of the floret. (M = upper portion of 

superposed or satellite bundle of lemma median consisting solely of tracheary elements; POP = lower segments 

of posterior prongs descended from right and left of pistil plexus in Figure 20; s = sieve elements: t = tracheary 

elements; UP = middle layers of right and left lobes of upper plexus rising uniformly from the lower plexus of 

Figure 16.) 

festucoid grasses and does not widen to right and left after 

emerging from the placental bundle (Figure 22), as do 

festucoid grasses (Table 1, row 15). Despite these two 

similarities in the placental bundles of Leersia and Raddia, that 

of Raddia differs from that of Leersiu and that of festucoid 

grasses because the placental bundle in Raddia exceeds the tip 

of the ovule (Table 1, row 16; Figure 10, level 1072). 

The placental bundle and all major components of the 

vascular system of the festucoid grasses, except the lower 

plexus, contains the system of occluded, anomalous tracheary 

elements: the xylem discontinuity (Table 1, row 17). Raddia 

and the oryzoid grasses lack such a component, a fact that 

substantiates the diagnostic value of this component in 

delimiting the festucoid grasses from the rest of the family. Zee 

and O’Brien (1970) were prescient in their understanding of the 

significance of this component. 

In considering the interconnection of the units of the vascular 

system of the festucoid and oryzoid grasses, Pizzolato (1989b) 

indicates that both groups bar the path of tracheary elements to 

the stamens and pistil. Festucoid grasses achieve this end with 

the xylem discontinuity. Oryzoid grasses do so without it but 

with a system of autonomous stamen and pistil components 

instead. On the other hand, Raddia, and presumably the 

Olyreae and bamboos in general, seem to have the most 

integrated, woven system of sieve and tracheary elements. 

Hence, there may exist fundamental differences in achieving 

anthesis and grain-filling between the bamboos and the rest of 

the grasses. 

A succinct judgment of the similarities and differences in 

florets of Raddia of the Olyreae and those of the investigated 

festucoid and oryzoid grasses is that Raddia in its rachilla 

vascular components resembles the Festucoideae but in its 
24 SMITHSO" CONTRIBUTIONS TO BOTANY 

FIOURE 18.-Facsimile of female floret vascular system at 214-268 pn above floret base showing the upper 

levels of the upper plexus (UP), middle levels of the posterior prongs (POP) or lobes descending from the pistil 

plexus, and merger of Iodide traces (~700). Sieve and tracheary elements indicated by paired dots comprise the 

horizontal connection between the anterior segments of the upper plexus; this connection bridges the parenchyma 

gap over M of Figure 17. Scale (3 pn long) remains in parenchyma in same relative position throughout all of 

the levels of the floret, (A = anterior trace of anterior Iodides; UO = all traces of the left anterior Iodide; PEP 

= peneposterior traces of both anterior lodicules; PLO = trace of posterior lodicule; RLO = all traces of right 

anterior lodide; s = sieve elements; t = tracheary elements.) 

pistil components resembles the Oryzoideae. However, in some 

of these upper and lower segments, Raddia differs from the 

group it more closely resembles. Thus, a fair statement is that, 

based on components of the floret vascular system, Raddia is 

no more oryzoid than it is festucoid. 

FLORET VASCULAR ANATOMY SUGGESTS THAT Raddia 

BELONGS TO THE OLYREAE OF THE BAMBUSOIDEAE 

Soderstrom and Zuloaga (1985) and Soderstrom and Ellis 

(1987) have summarized the characteristics of the spikelet that 

delimit the tribe Olyreae from the other bamboos. Based on 

these features, Raa'dia is a genus of the Olyreae. Features of 

the floret vascular system just enumerated were not used in this 

assignment. Now that the floret vascular system is known for 

Raddia, comparisons in its features can be made with the few 

olyroid genera whose florets have been studied anatomically. 

Calderon & Soderstrom (1973) studied the spikelets of 

Maclurolyra Calderon and Soderstrom, 1973, and Butzin 

(1965) studied the female spikelet of Olyra L., 1759. Both 

genera, like Ruddia, belong to the Olyreae. In spikelet 

morphology and anatomy, they are similar. The male florets of 

Maclurolyra and Olyra are smaller than the females and lack 

glumes. There are two vascularized anterior lodicules, a 

vascularized posterior lodicule, and three vascularized stamens 

in the male floret of Maclurolyra. Maclurolyra differs slightly 

from the single studied spikelet of Raa'dia in that reduced 

glumes, three staminodia, and an aborted pistil may be present 

in the male. The female floret of Maclurolyra and Olyra has 

vascularized glumes, and three vascularized lodicules, and 

three avascular staminodia. Calderon and Soderstrom (1973) 

indicate that one trace joins each lodicule to the rest of the 
NUMBER 78 25 

FIGURE 19.-Facsimile of female floret vascular system at 268-341 pn above floret base showing the vascular 

pmgs descending from the pistil plexus of Figure 20 (~700). During descent, RPP and LPP become the posterior 

pmgs of Figure 18. During descent, AP merges with the horimtal connection acmss the anterior of Figure 18. 

Dalts show where clusters of sieve elements so marked in Figure 20 descended from the pistil plexus to contribute 

to AP, RPP, and LF’P. Scale (3 pm long) remains in parenchymain same relative position throughout all the levels 

of the floret. (AP = pair of anterior vascular prongs descending from anterior of pistil plexus of Figure 20; LPP 

= pair of vascular prongs descending on the left and posterior from the pistil plexus of Figure 2Q RPP = pair of 

vascular prongs descending on the right and posterior from the pistil plexus of Figure 20; s = sieve elements; t = 

tracheaty elements.) 

system. However, their cleared unsectioned material did not 

show the two (male) or three (female) traces that merge into the 

rest of the system from the anterior lodicules of Raddia. In 

sectioned female florets of Olyra, Butzin (1965) saw the three 

traces from each anterior lodicule that occur in Raddia, as well 

as the solitary trace from the posterior lodicule. Calderon and 

Soderstrom (1973) and Butzin (1965) did not identify the 

vascular tissue of the lodicule traces of Maclurolyra and Olyra. 

The cleared pistils of Maclurolyra revealed to Calderon and 

Soderstrom (1973) a placental bundle whose mature xylem and 

phloem ended at the base of the ovule, and two posterolateral 

(stylar) bundles of xylem and phloem. After examining several 

species of five genera in the Olyreae including Maclurolyra 

and Olyra but not Raddia, Calderon and Soderstrom (1973:24) 

concluded that a “gynoecium with three vascular traces seems 

to be the general rule for the Olyreae,” a conclusion that the 

pistil of Ruddia fully supports. The pistil vasculature of the 

Olyreae differs with that of the woody bamboos, which may 

have an anterior bundle as well as anterolaterals besides the 

placental bundle and two posterolaterals of the Olyreae (Arber, 

1926; Chandra, 1963). The study of Ruddia showed that the 

posterolaterals or stylar bundles attach to the pistil plexus, as 

occurs in the Oryzoideae, not to the placental bundle as occurs 

in the Festucoideae (Table 1). Although Calderon and 

Soderstrom (1973) were unaware of this character in the 

Olyreae when they studied Maclurolyra, their figure 13E of a 

cleared pistil shows this feature. 

Although Calderon and Soderstrom (1973) are unclear if the 

placental bundle ascends beyond the ovule as happens in 

Raddia, their “connecting strand” likely is the region of merger 
26 SMITHSONIAN CONTRIBUTIONS TO BOTAh’Y 

FIGURE 20.-Facsimile of female floret vascular system at 341-424 pm above floret base showing the pistil 

plexus (~800). Paired dots show core of sieve elements among tracheary elements but continuous with sieve 

elements of the periphery of the pistil plexus; as pistil plexus contracts to form the placental bundle of Figure 21, 

its anterior sieve elements (paired dots in Figure 21) connect at this sieve-elanent core. Darts show whence 

clusters of sieve elements descend to connect with those so marked in Figure 19. Scale (3 pm long) remains in 

parenchyma in same relative position throughout all the levels of the floret. (LPL = site of merger of left 

posterolateral (stylar) bundle with pistil plexus; RPL = site of merger of right posterolateral (stylar) bundle with 

pistil plexus; s = sieve elements; t = tracheary elements.) 

of the placental bundle above the ovule with the stylar core as 

shown for Raddia in Figure 11, level 1072. The study of 

Raddia supported by Calderon and Soderstrom’s (1973) study 

of the pistil of Maclurolyra indicates that the placental bundle 

ascends a little above the ovule before being superseded by the 

stylar core. Among the non-olyroid bamboos, there is variation 

in this character (Arber, 1926; Chandra, 1963). 

Only two earlier studies exist in which florets from the 

Olyreae or its allied tribe, the Streptochaeteae of Soderstrom 

and Ellis (1987), were studied is sectioned material. When 

these papers are examined in light of the Raddia study, some 

pertinent similarities in the vascular systems of these olyroid 

bamboos are revealed. In Butzin’s (1965) study of the female 

spikelet of Olyra, figure 5, is oriented so that the floret’s 

posterior is to the left of the page. His figure 5E is nearly 

identical to Figure 10, level 1 of Raddia (herein) showing the 

rachilla with bundles 3, 2, and 1 surrounded by the glumes. 

Butzin’s (1965) figure 5F is virtually identical to Figures 14 and 

15 of Raddia showing bundles 3, 2, and 1 simultaneously 

forming their respective traces to M and the lemma laterals 

while they form the lower plexus. 

Butzin’s (1965) comment that the lemma and palea lateral 

traces on each side of the rachilla connect closely with each 

other and the bundle of Olyra corresponding to bundles 1 (or 2) 

of Raddia relates well to the pertinent observations in Raddia. 

In Ruddia, bundle 1 (or 2) occurs in the rachilla as a lemma left 

(or right) lateral. The other member of the lemma lateral pair 

merges so soon with bundle 1 (or 2) that it is difficult to be 

certain which one of the lateral pair was the original bundle 1 

(or 2). Then the left (or right) lateral of the palea merges with 

the mergers of the paired lemma laterals as they are 

proliferating to form the flanks of the lower plexus of Ruddia 
NUMBER 78 27 

FIOURES 21, 22.-Facsknile of female floret vascular system at 424-461 and 461-488 pn above floret base 

showing the upper levels of the pistil plexus and the lower levels of the placmtal bundle (~700). Sieve elements 

marked with paired dots are continuous with those so marked in Figure 20. With ascent from Figure 20, the pistil 

plexus contracts toward the posterior and opens at the anterior to become the placental bundle. Scale (3 pn long) 

remains in parenchyma in same relative position throughout all the levels of the floret. (s = sieve elements; t = 

tracheary elements.) 

(Figures 13-16). “Deck- und Vorspelzennervatur stehen also 

in engem Konnex” [thus the lemma and palea traces are closely 

connected] in the rachilla of Olyra (Butzin, 196536) and 

Raddia. 

Butzin’s (1965) figure 5G is like Figure 16 of Raddia 

because both show the top layers of the lower plexus and the 

superposed portion of the lemma median. Butzin’s (1965) 

figure ~L,M indicates that, as in Raddia, the posterolaterals are 

gynobasic. Although Calderon and Soderstrom (1973) also 

studied Butzin (1965), they were unable to make revealing 

comparisons with his figure 5 because they lacked comparative 

sectioned material of Maclurolyra. The posterolaterals merge 

at the flanks of the pistil plexus as they do in Raddia. As in 

Raddia there is no other bundle in the pistil besides the 

posterolaterals and the placental bundle (Butzin, 1965). 

Arber’s (1929) study of the sectioned perfect floret of 

Streprochaeta, which she orients with the anterior to the bottom 

of the page, is also informative when compared with Raddia. 

Bundles 3,2, and 1 are arranged in the rachilla at the floret base 

in Arber’s (1929) figure 4~2 of Srreptochaeta just as they are in 

Raddia and Olyra. Arber’s (1929) figure 4A3-5 indicates that 

M from bundle 3 follows the same tortuous course below a 

lemma pocket as does M in the male floret of Raddia. Arber’s 

figure 4A5 is like a sketch of Figure 16 of Raddia showing the 

superposed portion of M between the upper levels of the lower 

plexus. Arber’s (1929) figure 4~6 of Streprochaera suggests the 

gynobasic nature of the posterolateral attachment of Raddia, 

Olyra, and Maclurolyra. The anterior bundle of Streptochaeta 

distinguishes the Streptochaeteae from the Olyreae. 

The similarities of the floret vascular system of Raddia with 

those revealed by the earlier studies of Streprochaeta (Arber, 

1929), Olyra (Butzin, 1965) and Maclurolyra (Calderon and 

Soderstrom, 1973) indicate that the floret vascular system of 

Raddia typifies the Olyreae and the Streptochaeteae. Moreover, 

the similarities of the floret vascular system of these tribes with 

the corresponding characters recorded for the woody bamboos 

(Arber, 1926, 1929; Chandra, 1963; Butzin, 1965) support the 

inclusion of the Olyreae and Streptochaeteae among the 

bamboos by Soderstrom and Ellis (1987), who used a suite of 

other morphological and anatomical characters including the 

supernumerary midrib bundles of Page (1947), Metcalfe 

(1960). and Renvoize (1985). 

FLORET VASCULAR ANATOMY SUGGESTS THAT Raddia 

AND THE OLYREAE ARE NOT PANICOID GRASSES 

If the vascular system in both florets of Raddia and its allies 

is compared with that of Panicum L., 1753 (Pizzolato, 1983), 

Raddia is found strikingly different from Panicum and more 

like the genera whose florets have been analyzed three 

dimensionally (Table 1). The palea traces of these nonpanicoid 

grasses do not descend the rachilla beyond the floret base 

without linking with other traces of the rachilla (Pizzolato, 

l984,1987,1988,1989a, b). The palea traces must first be part 

of the lower plexus (Phalaris) or be obstructed by the lower 

plexus (Raddia, Anthoxanthum), or be obstructed by traces of 

the lemma median (Leersia, Alopecurus) or laterals (Phleum). 

In Panicum, the palea traces and lemma laterals do not 

interconnect with the rest of the floret system in the rachilla at 

the floret base. Apparently Chandra (1962) and Clifford (1987) 

attempt to make similar distinctions between panicoid and 

nonpanicoid grasses without having analyzed the floret 

vascular system three dimensionally. 

In nonpanicoid florets, the components of the vascular 
28 SMITHSONIAN CONTRIBUTIONS TO BOTANY 

D. Pistil components 

RLO 

PB 

5. 

Prongs 

B. CT Upper plexus C. 9 Upper plexus with descending 

pistil plexus prongs 

to upper plexus 

A 

M 

A. Lower plexus 
NUMBER 78 29 

From 23.-Diagrams of the components of the vascular system of the male 

floret and the fanale floret. In the lower plexus, the subsidiary bundles of M are 

shown united as they occur in the female floret, not discrete as they occur in the 

male floret. (AS = anterior stamen trace; L = lateral traces of the lemma; LLO 

= traces of left anterior lodicule; LP = left posterolateral bundle; L!3 = trace of 

left stamen; M = median trace of lemma; P = palea trace; PB =placental bundle; 

PLO = trace of posterior lodicule; PP = pistil plexus; Ru) = traces of right 

anterior lodicule; RP = right posterolateral bundle; RS = trace of right stamen; 

1.2.3 =bundles 1,2,3.) 

system above the lemma median merge axially (directly) with 

bundle 3; but the higher components of Panicum merge with 

the lemma median diagonally, giving the system ai ungual 

morphology (Pizzolato, 1983). The floret of Panicum lacks a 

lower plexus and an upper plexus in vivid contrast to the 

condition in Raddia. The stamen traces of Panicum appear 

autonomous as in Leersia; thus, there is a gap in the rachilla 

between the flanking stamens of Panicum not allowable by the 

stamen traces to the upper plexus of the male floret of Raddia 

or of a festucoid grass. 

Additionally, there is a marked distinction between the 

course of the placental bundle between Raddia and the panicoid 

grasses. In Raddia and Maclurolyra (Calderon and Soderstrom, 

1973), the placental bundle ascends the length of the ovary but 

in the Paniceae, the placental bundle merges with the ovule at 

the base of the ovary (Zee and O’Brien, 1971; Giles et al., 

1975). 

Therefore, anatomy of the floret vascular systems does not 

support placing the Olyreae among the Paniceae despite the 

fact that both groups host similar rust fungi (Savile, 1987). 

Floret vascular anatomy, certainly as esoteric (Macfarlane and 

Watson, 1982) as rust susceptibility, supports the schemes of 

natural classification of Hilu and Wright (1982) and Watson et 

al. (1985) that place the Olyreae away from the Panicoideae. 

Root anatomy supports this conclusion from floret vasculature, 

for Raechel and Curtis (1990) observe that certain genera of the 

Olyreae including Raddia have several features that vary from 

the panicoid type. 

FLORET VASCULAR ANATOMY SUGGESTS THAT 

Brachyelytrum IS NOT AN OLYROID GRASS 

The association of superposed bundles with the lemma 

median of male and female florets of Raddia, and the 

occurrence of these bundles in the midribs of genera of the 

Olyreae (Soderstrom and Zuloaga, 1985) including Raddia 

strongly support the inclusion of the Olyreae among the 

Bambusoideae as suggested by Page (1947), Metcalfe (1960), 

and Soderstrom and Ellis (1987). Therefore, the absence of 

superposed midrib bundles (Campbell et al., 1986) from the 

Brachyelytrum Palisot de Beauvois, 1812 of “chequered 

classificatory history” (Macfarlane and Watson, 1980650) 

does not support its inclusion in the Olyreae. 

That the pistil of Raddia lacks an anterior bundle but has two 

posterolaterals besides the placental bundle supports the 

placement of Raddia among the Olyreae according to the 

conclusions of Calderon and Soderstrom (1973:24) that 

“gynoecium with three vascular traces seems to be the general 

rule for the Olyreae.” The suggestion that Brachyelytrum be 

included with the Olyreae (Campbell et al., 1986) is not 

supported by Belk (1939:72) who noted that “three vascular 

strands in addition to the ovule supply bundle are present in the 

gynoecium.” Moreover, Belk’s (1939) figures 294-300 plainly 

show the anterior bundle in the pistil of Brachyelytrum. 

Furthermore, Brachyelytrum should be excluded from the 

Olyreae because Belk (1939) indicates that the ovule supply 

bundle (placental bundle) does not extend beyond the ovule, 

whereas the reverse is probably true of Maclurolyra and 

definitely of Raddia of the Olyreae. Belk (1939) shows that 

Brachyelytrum lacks the stylar core which supersedes the 

placental bundle of Raddia and Maclurolyra of the Olyreae and 

many other bamboos. Wherever the affinities of Brachyelytrum 

lie, they are probably not with the Olyreae. 

FLORET VASCULAR ANATOMY SUGGESTS THAT Raddia 

AND THE OLYREAE ARE NOT ORYZOID GRASSES 

Using a multitude of characters, character states, and genera, 

Watson et al. (1985) place olyroid grasses including Raddia, 

Maclurolyra, and Olyra together with oryzoid grasses including Leersia, Luriola Jussieu, 1789, and Oryza into a supertribe 

separate from another supertribe containing woody bamboos. 

By placing Streptochaeta into the supertribe of woody 

bamboos, away from the Olyreae, Watson et al. (1985) discount 

the olyroid affinity of Streprochaeta. 

However, the floret vascular system of Raddia indicates that 

olyroid grasses should be classified separately from the oryzoid 

grasses. The olyroid grasses are no more similar to the oryzoid 

grasses in floret vasculature than the olyroid grasses are to the 

festucoid grasses (Table 1). Moreover, Table 1 indicates three 

features of floret vasculature in the Olyreae not found in either 

the Oryzoideae or Festucoideae of Hilu and Wright (1982). The 

floret vascular systems of Raddia and of the herbaceous 

bamboos Streptochaeta (Arber, 1929), Olyra (Butzin, 1965), 

and Maclurolyra (Calderon and Soderstrom, 1973) support the 

notion of a close affinity of the olyroid grasses-not 

encumbered by the oryzoid grasses-with the woody bamboos 

suggested by the anatomical and systematic studies of Page 

(1947), Metcalfe (1960), Soderstrom and Ellis (1987), and Hilu 

and Wright (1982). Although Hilu and Wright (1982) included 

fewer characters and genera in their scheme of classification, as 

summarized in their Figures 1 and 6, than did Watson et al. 

(1985), the former system is harmonious with the affinities 

deduced from floret vasculature for the Festucoideae, the 

Oryzoideae, and the Bambusoideae including Olyra. Connor 

(1979) and Stebbins (1987) overemphasize the importance of 

the frequently similar stamen number among bambusoid and 

oryzoid grasses as an indicator of their close affinity. The 
30 SMITHSOh" CONTRIBUTIONS TO BOTANY 

autonomous connections of the stamen traces of Leersia 

(Pizzolato, 1989b) to the rachilla vascular system, without an 

upper plexus, is too different from the intimate connection of 

the stamen traces of the female floret of Raddia, via an upper 

plexus, to be obscured by similarity of stamen number. 

Pertinent to these conclusions are four bits of data as esoteric 

(Macfarlane and Watson, 1982) as floret vascular systems. 

First, Savile (1987) observed that rusts that parasitize Leersia 

produce teliospores very different from those that parasitize 

Olyra. Second, Hamby and Zimmer (1988) were puzzled that 

nucleotide sequences of RNA's from Oryza and Arundinaria 

Michaux, 1803, a woody bamboo (Tbcker, 1988), were not as 

similar as the scheme of Watson et al. (1985) suggests the 

sequences should be. Third, Esen and Hilu (1989) indicate that 

the low immunological similarity of prolamin seed proteins 

from another woody bamboo and Oryza opposes the idea of the 

Oryzoideae as part of the Bambusoideae. Fourth, Bhanwra 

(1988) noted features in the microsporangia and ovule of Oryza 

which keep the genus apart from some species of woody 

bamboos. These sets of esoteric distinctions are consistent with 

the differences noted between vascular systems of florets in the 

Oryzoideae and in the Olyreae. 
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