bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogenetic relationships of Rhododendroideae (Ericaceae)
Authors: Kron Kathleen A.
Published: April 2006

The Rhododendroideae are usually recognized as a subfamily within Ericaceae. This group has been considered primitive (i.e., occupying the ancestral or basal position relative to all other Ericaceae) due to the occurrence of separate petals in several taxa, deciduous corollas, and septicidally dehiscent capsules. Previous molecular studies using rbcL and nr18s sequences have indicated that Rhododendroideae may be paraphyletic and cladistically derived (i.e., the relative position in the geneology of Ericaceae is not basal). The matK sequences of 42 taxa from traditional Rhododendroideae and potentially related clades were obtained via standard gene amplication and double‐stranded dideoxy sequencing. Phylogenetic analyses of these sequences using Actinidia chinensis as the outgroup indicate that the Rhododendroideae are paraphyletic. Trees obtained in the analyses indicate an expanded rhododendroid clade that includes four major subclades—empetroid, rhodo, ericoid, and phyllodocoid. The ericoid clade is sister to the phyllodocoid clade and the empetroid clade is sister to the rhodo clade. Relationships within the clades are generally well resolved except within the rhodo clade where matK data indicate that Rhododendron is probably paraphyletic. Daboecia and Calluna are included within the ericoid clade; Erica is paraphyletic. Cassiope lies outside the rhododendroid clade. The relationships indicated by the matK data suggest that sympetalous flowers are likely plesiomorphic within rhododendroids.
Male‐specific DNA in the dioecious species Atriplex garrettii (Chenopodiaceae)
Authors: Ruas Claudete F. , Fairbanks Daniel J. , Evans R. Paul , Stutz Howard C. , Andersen W. Ralph , Ruas Paulo M.
Published: April 2006

The mechanism of sex determination in dioecious species of the genus Atriplex (Chenopodiaceae) has not been determined. This paper reports the discovery of a male‐specific DNA fragment in the diploid dioecious species A. garrettii. DNA samples extracted individually from ten male and ten female plants were bulked by sex. Random amplified polymorphic DNA (RAPD) fragments were generated in the two bulks in order to identify markers that were polymorphic between male and female plants. A total of 158 decamer primers were tested. A 2075 base‐pair (bp) male‐specific DNA fragment generated with the OPAF‐14 primer was identified. The fragment was cloned and partially sequenced and 24‐mer primers that exclusively amplified this fragment were constructed. When 124 male plants, 126 female plants, and one hermaphroditic plant were tested individually, the male‐specific 2075‐bp DNA fragment was present in the hermaphrodite and all but one of the male plants, and was absent in all female plants. A smaller DNA fragment (~1800 bp) that was homologous to the 2075‐bp fragment was amplified from the single male plant that lacked the 2075‐bp fragment. Cytogenetic analysis revealed no apparent heteromorphic sex chromosomes. These observations suggest that sex determination in A. garrettii is genetic, with no evidence of heteromorphic sex chromosomes.
Nickel hyperaccumulation by Thlaspi montanum var. montanum (Brassicaceae): a constitutive trait
Authors: Boyd Robert S. , Martens Scott N.
Published: April 2006

Adaptations to particular stresses may occur only in populations experiencing those stresses or may be widespread within a species. Nickel hyperaccumulation is viewed as an adaptation to high‐Ni (serpentine) soils, but few studies have determined if hyperaccumulation ability is restricted to populations from high‐Ni soils or if it is a constitutive trait found in populations on both high‐ and low‐Ni soils. We compared mineral element concentrations of Thlaspi montanum var. montanum plants grown on normal and high‐Ni greenhouse soils to address this question. Seed sources were from four populations (two serpentine, two non‐serpentine) in Oregon and northern California, USA. Plants from all populations were able to hyperaccumulate Ni, showing Ni hyperaccumulation to be a constitutive trait in this species. Populations differed in their ability to extract some elements (e. g., Ca, Mg, P) from greenhouse soils. We noted a negative correlation between tissue concentrations of Ni and Zn. We suggest that the ability to hyperaccumulate Ni has adaptive value to populations growing on non‐serpentine soil. This adaptive value may be a consequence of metal‐based plant defense against herbivores/pathogens, metal‐based interference against neighboring plant species, or an efficient nutrient scavenging system. We suggest that the Ni hyperaccumulation ability of T. montanum var. montanum may be an inadvertent consequence of an efficient nutrient (possibly Zn or Ca) uptake system.
Biomechanics and functional anatomy of hollow‐stemmed sphenopsids. I. Equisetum giganteum (Equisetaceae)
Authors: Spatz Hanns‐Christ of , Köhler Lothar , Speck Thomas
Published: April 2006

The hollow stem of Equisetum giganteum owes its mechanical stability to an outer ring of strengthening tissue, which provides stiffness and strength in the longitudinal direction, but also to an inner lining of turgid parenchyma, which lends resistance to local buckling. With a height >2.5 m isolated stems are mechanically unstable. However, in dense stands individual stems support each other by interlacing with their side branches, the typical growth habit of semi‐self‐supporters.
The role of mycorrhizal fungi and microsites in primary succession on Mount St. Helens
Authors: Titus Jonathan H. , Moral Roger del
Published: April 2006

This study was designed to examine the role of vesicular‐arbuscular mycorrhizae (VAM) and microsites on the growth of pioneer species. Flat, rill, near‐rock, and dead lupine microsites were created in plots in barren areas of the Pumice Plain of Mount St. Helens. VAM propagules were added to the soil in half of the plots. Six pioneer species were planted into both VAM and non‐VAM inoculated microsites. Plants in dead lupine microsites were greater in biomass than those in flat, rill, and near‐rock microsites. Significant effects of VAM on plant biomass did not occur. Microsites continue to be important to plant colonization on the Pumice Plain, but VAM do not yet appear to play an important role. This may be due to limited nutrient availability and the facultatively mycotrophic nature of the colonizing plant species. It is unlikely that VAM play an important role in successional processes in newly emplaced nutrient‐poor surfaces.
Evolution of novel morphological and reproductive traits in a clade containing Antirrhinum majus (Scrophulariaceae)
Authors: Reeves Patrick A. , Olmstead Richard G.
Published: April 2006

Phylogenetic analysis of DNA sequences of the chloroplast genes rbcL and ndhF revealed a highly supported clade composed of the families Plantaginaceae, Callitrichaceae, and Hippuridaceae in close association with the model organism Antirrhinum majus and other members of family Scrophulariaceae. Plantago has miniature actinomorphic wind‐pollinated flowers that have evolved from zygomorphic animal‐pollinated precursors. The aquatic Hippuridaceae have reduced wind‐pollinated flowers with one reproductive organ per whorl, and three, rather than four, whorls. In monoecious aquatic Callitrichaceae, further reduction has occurred such that there is only one whorl per flower containing a single stamen or carpel. Optimization of character states showed that these families descended from an ancestor similar to Antirrhinum majus. Recent studies of plant developmental genetics have focused on distantly related species. Differences in the molecular mechanisms controlling floral development between model organisms are difficult to interpret due to phylogenetic distance. In order to understand evolutionary changes in floral morphology in terms of their underlying genetic processes, closely related species exhibiting morphological variation should be examined. Studies of genes that regulate morphogenesis in the clade described here could aid in the elucidation of a general model for such fundamental issues as how changes in floral symmetry, organ number, and whorl number are achieved, as well as providing insight on the evolution of dicliny and associated changes in pollination syndrome.
Preferential states of longitudinal tension in the outer tissues of Taraxacum Officinale (Asteraceae) peduncles
Authors: Niklas Karl J. , Paolillo Dominick J.
Published: April 2006

We tested Wilhelm Hofmeister's hypothesis that the outer layers of herbaceous stem tissues are held in a preferential state of longitudinal tension by more internal stem tissues that are held in a reciprocal state of compression. We measured (1) the biaxial stiffness of dandelion peduncles that were barometrically inflated with a Scholander pressure bomb, and (2) the stiffness and mechanical behavior of different layers of tissues that were surgically manipulated as longitudinal strips placed in uniaxial tension. Hofmeister's hypothesis predicts that stems will shorten and expand in girth as their volume transiently increases (due to barometric or hydrostatic inflation), that they will longitudinally rupture when excessively inflated, and that the principal stiffening agents in their outer tissues will be aligned in the longitudinal direction with respect to stem length. Our experiments confirmed these predictions: (1) the longitudinal strains observed for inflated peduncles were negative and smaller than the circumferential strains such that stems contracted in length and expanded in girth, (2) peduncles longitudinally ruptured when excessively inflated, (3) surgical experiments indicated that the epidermis was stiffer in longitudinal tension than any other immature peduncle tissue and was as stiff as any other tissue region in mature stems, and (4) microscopic analyses showed that the net orientation of cellulose microfibrils in the cell walls of the outer region of stem tissues was parallel to stem length. A strong positive correlation existed between the tensile stiffness of tissues and the net orientation of cell wall microfibrils.

A biomechanical model for the dandelion peduncle wall was constructed based on the thermal behavior of a cross‐ply unidirectional composite material whose adjacent plies contain orthogonally oriented stiffening agents. This model accurately predicted the magnitudes of the tensile stiffness of different tissue regions, the proportional thickness of these regions, and the formation of a bulge in the epidermis and a crease on the inner surface of the stem wall when the innermost region of stem tissues was transversely cut. For each of its variants possessing an outer ply with longitudinally aligned stiffening agents (i.e., a 0° ply) and containing at least one internal ply with transversely aligned stiffening agents (i.e., a 9° ply), the model predicted a state of preferential longitudinal tension in the 0° ply (or plies) and of preferential longitudinal compression in the 9° ply as posited by Hofmeister's hypothesis.
Postglacial migration and the loss of allozyme variation in northern populations of Asclepias Exaltata (Asclepiadaceae)
Authors: Broyles Steven B.
Published: April 2006

The recent Wisconsin glaciation has provided opportunities for examining the effects of postglacial recolonization on the population genetics of plant and animal communities. In this study allozyme variation was examined in 19 populations of the herbaceous perennial Asclepias exaltata occurring in previously glaciated regions of North America. These northern populations of A. exaltata possess significantly fewer polymorphic loci (46.3 ± 2.7; mean ± 1 SD), alleles per polymorphic locus (1.84 ± 0.24), and expected heterozygosity (0.133 ± 0.031) than populations found in the Pleistocene refugium in the southern Appalachians. Population‐level allozyme diversity decreased linearly from south to north and from east to west. Nineteen uncommon alleles previously observed in southern Appalachian populations were undetected in the northern region. Seven common alleles exhibited a clinal change in allele frequency. Of these, only Pgd‐1a and Mnr‐1c were at low‐frequency in the southern Appalachians and increased significantly with increasing latitude and longitude, respectively. Despite this loss of allozyme diversity following postglacial migration, northern populations of A. exaltata have higher allozyme diversity and lower population differentiation (Gst = 0.117) than mean values for other long‐lived herbaceous perennials. Increased habitat fragmentation in northern regions and potential habitat loss in the southern Appalachians are likely to reduce the historically rich gene pool that has provided the genetic stock for postglacial recoveries.
Latitudinal population differentiation in two species of Solidago (Asteraceae) introduced into Europe
Authors: Weber Ewald , Schmid Bernhard
Published: April 2006

Solidago altissima and S. gigantea were introduced from North America to Europe ~250 yr ago and are now considered aggressive weeds in abandoned fields and conservation areas. We studied patterns of genetic differentiation in these two species along their present latitudinal range in Europe (44°–61° N). Two generations of clonally propagated ramets from randomly selected genets of 24 populations of each species were grown in a common‐garden experiment at latitude 47° N from 1991 to 1992. Both species showed significant variation among populations in morphological and life‐history characters: at this southern location, plants from northern populations were smaller and flowered earlier than plants from southern populations. The gradient of clinal variation was more pronounced in the second year of cultivation than in the first and was steeper in S. altissima than in S. gigantea. Within‐population variation among genotypes was significant for most characters in the case of S. altissima. Phenological rate (reciprocal of days to flowering) and size at maturity showed a significant negative correlation among populations but not among genotypes within populations, indicating that genetic trade‐offs may occur at one but not another infraspecific level. We suggest that the pattern of among‐population variation reflects rapid adaptive population differentiation after introduction of the species to Europe.
Fossil Clusiaceae from the Late Cretaceous (Turonian) of New Jersey and implications regarding the history of bee pollination
Authors: Crepet William L. , Nixon Kevin C.
Published: April 2006

The Turonian flora from Sayreville New Jersey includes one of the world's most diverse assemblages of Cretaceous angiosperm flowers. This flora is made even more interesting by its association with a large insect fauna that is preserved by charcoalification as well as in amber. Floral diversity includes numerous representatives of Magnoliidae, Hamamelididae, Rosidae, Dilleniidae, and Asteridae (Ericales sensu lato). Included are hypogynous, five‐merous flowers with uniseriate hairs on the pedicels and stamens in bundles most frequently borne opposite the petals. There is considerable variation in filament length, and some filaments are branched. On some anthers, strands of residue, suggesting the former presence of a liquid of unknown nature, partially occlude the apparent zone of dehiscence. In other cases, open anthers are fully occluded by an amorphous substance. pollen is rarely found associated with anthers, but is common on stigmatic surfaces. pollen is prolate and tricolporate with reticulate micromorphology. The superior syncarpous ovary is five‐carpellate with axile/intruded parietal placentation and numerous anatropous ovules/carpel. Ovary partitions have closely spaced, parallel ascending channels (secretory canals?), and there are apparent secretory canals/cavities in receptacles, sepals, and petals. Individual stigmas are cuneiform with a central groove and eccentrically peltate. Styles are short and fused. In aggregate, the stigmas form a secondarily peltate stigma. Seeds have a reticulate sculpture pattern, a pronounced raphe, and funicular arils with sculpture similar to the seeds. phylogenetic analyses of several data matrices of extant taxa place this fossil in a monophyletic group with the modern genera Garcinia and Clusia within the Clusiaceae. As such, these fossils represent the earliest fossil evidence of the family Clusiaceae. Some modern Clusiaceae are notable, in particular, for their close relationship with meliponine and other highly derived bee pollinators; the fossil flowers share several characters that suggest a similar mode of pollination. This possibility is consistent with other floral and insect data from the same locality.
Variability in leaf optical properties among 26 Species From A Broad Range Of Habitats
Authors: Knapp Alan K. , Carter Gregory A.
Published: April 2006

Leaves from 26 species with growth forms from annual herbs to trees were collected from open, intermediate, and shaded understory habitats in Mississippi and Kansas, USA. Leaf optical properties including reflectance, transmittance, and absorptance in visible and near infrared (NIR) wavelengths were measured along with leaf thickness and specific leaf mass (SLM). These leaf properties and internal light scattering have been reported to vary with light availability in studies that have focused on a limited number of species. Our objective was to determine whether these patterns in leaf optics and light availability were consistent when a greater number of species were evaluated. Leaf thickness and SLM varied by tenfold among species sampled, but within‐habitat variance was high. Although there was a strong trend toward thicker leaves in open habitats, only SLM was significantly greater in open vs. understory habitats. In contrast, leaf optical properties were strikingly similar among habitats. Reflectance and reflectance/transmittance in the NIR were used to estimate internal light scattering and there were strong relationships (r2 > 0.65) between these optical properties and leaf thickness. We concluded that leaf thickness, which did not vary consistently among habitats, was the best predictor of NIR reflectance and internal light scattering. However, because carbon allocation to leaves was lower in understory species (low SLM) yet gross optical properties were similar among all habitats, the energy investment by shade leaves required to achieve optical equivalence with sun leaves was lower. Differences in leaf longevity and growth form within a habitat may help explain the lack of consistent patterns in leaf optics as the number of species sampled increases.
The chaparral vegetation in Mexico under nonmediterranean climate: the convergence and Madrean‐Tethyan hypotheses reconsidered
Authors: Valiente‐Banuet Alfonso , Flores‐Herna´ndez Noe´ , Verdu´ Miguel , Da´vila Patricia
Published: April 2006

A comparative study between an unburned evergreen sclerophyllous vegetation located in south‐central Mexico under a wet‐summer climate, with mediterranean regions was conducted in order to re‐analyze vegetation and plant characters claimed to converge under mediterranean climates. The comparison considered floristic composition, plant‐community structure, and plant characters as adaptations to mediterranean climates and analyzed them by means of a correspondence analysis, considering a tropical spiny shrubland as the external group. We made a species register of the number of species that resprouted after a fire occurred in 1995 and a distribution map of the evergreen sclerophyllous vegetation in Mexico (mexical) under nonmediterranean climates.

The Tehuaca´n mexical does not differ from the evergreen sclerophyllous areas of Chile, California, Australia, and the Mediterranean Basin, according to a correspondence analysis, which ordinated the Tehuaca´n mexical closer to the mediterranean areas than to the external group.

All the vegetation and floristic characteristics of the mexical, as well as its distribution along the rain‐shadowed mountain parts of Mexico, support its origin in the Madrean‐Tethyan hypothesis of Axelrod. Therefore, these results allow to expand the convergence paradigm of the chaparral under an integrative view, in which a general trend to aridity might explain floristic and adaptive patterns detected in these environments.
Studies in Neotropical paleobotany. XII. A palynoflora from the Pliocene Rio Banano Formation of Costa Rica and the Neogene vegetation of Mesoamerica
Authors: Graham Alan , Dilcher David L.
Published: April 2006

An assemblage of 17 identified and four unknown pollen and spore types is reported from the Pliocene Rio Banano Formation of southeastern Costa Rica. The most abundant are monolete fern spores, Palmae, cf. Antrophyum, Symphonia, Pelliceria, Lacmella (previously unreported in the fossil record), Alchornea, and Sabicea. These arrange into two paleocommunities—mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present ∼3500 mm, but less seasonal, and the MAT (mean annual temperature) at ∼27°C. No pollen taxa representing distinctly arid or high‐altitude vegetation was being blown or washed into the coastal depositional basin, and no pollen grains were recovered of northern temperate elements that are present in Neogene floras to the north in Guatemala and southeastern Mexico. These data are consistent with those from 12 other Miocene and Pliocene palynofloras from northern Latin America, indicating the late appearance of dry habitats and moderate paleoelevations and a progressive southward introduction of northern temperate elements with late Cenozoic cooling.
Pollination biology in a lowland dipterocarp forest in Sarawak, Malaysia. I. Characteristics of the plant‐pollinator community in a lowland dipterocarp forest
Authors: Momose Kuniyasu , Yumoto Takakazu , Nagamitsu Teruyoshi , Kato Makoto , Nagamasu Hidetoshi , Sakai Shoko , Harrison Rhett D. , Itioka Takao , Hamid Abang A. , Inoue Tamiji
Published: April 2006

Flowerings and flower visitors were observed continuously in a lowland dipterocarp forest in Sarawak, Malaysia, for 53 mo in 1992–1996. Flower visitors of 270 plant species were observed or collected, and pollinators were assessed by observing body contact to stigmas and anthers. We recognized 12 categories of pollination systems. Among them, plants pollinated by social bees included the largest number of species (32%) and were followed by beetle‐pollinated species (20%). Pollination systems were significantly related with some floral characters (flowering time of day, reward, and floral shape), but not with floral color. Based on the relationships between pollinators and floral characters, we described pollination syndromes found in a lowland dipterocarp forest. The dominance of social bees and beetles among pollinators is discussed in relation to the general flowering observed in dipterocarp forests of West Malesia. In spite of high plant species diversity and consequent low population densities of lowland dipterocarp forests, long‐distance‐specific pollinators were uncommon compared with the Neotropics.
RAPD variation in relation to population size and plant fitness in the rare Gentianella germanica (Gentianaceae)
Authors: Fischer Markus , Matthies Diethart
Published: April 2006

We investigated the distribution of genetic variation and the relationship between population size and genetic variation in the rare plant Gentianella germanica using RAPD (random amplified polymorphic DNA) profiles. Plants for the analysis were grown from seeds sampled from 72 parent plants in 11 G. germanica populations of different size (40–5000 fruiting individuals). In large populations, seeds were sampled from parents in two spatially distinct subpopulations comparable in area to the total area covered by small populations. Analysis of molecular variance revealed significant genetic variation among populations (P < 0.001), while genetic variation among subpopulations was marginally significant (P < 0.06). Average molecular variance within subpopulations in large populations did not differ significantly from whole‐population values. There was a positive correlation between genetic variation and population size (P < 0.01). Genetic variation was also positively correlated with the number of seeds per plant in the field (P < 0.02) and the number of flowers per planted seed in a common garden experiment (P < 0.051). We conclude that gene flow among natural populations is very limited and that reduced plant fitness in small populations of G. germanica most likely has genetic causes. Management should aim to increase the size of small populations to minimize further loss of genetic variation. Because a large proportion of genetic variation is among populations, even small populations are worth preserving.
Xylem feeding by spittlebug nymphs: some observations by optical and cryo‐scanning electron microscopy
Authors: Crews Laura J. , McCully Margaret E. , Canny Martin J. , Huang Cheng X. , Ling Lewis E. C.
Published: April 2006

The feeding of spittlebug nymphs (Philaenus spumarius) from mature xylem vessels was studied by optical and cryo‐analytical scanning electron microscopy. Feeding did not produce xylem embolisms and vessels remained liquid‐filled during the day. Saliva secreted by the insect forms a hardened lining (salivary sheath) between the stylet bundle and the plant tissues. This sheath is continuous through the hole made by the stylets as they enter a vessel, and it extends into the vessel and along its periphery beyond the breach. The sheath is heterogeneous, with a thin outer layer adjoining the plant tissues and a thicker layer that contacts the stylet bundle. Both layers give positive histochemical reactions for proteins and, in fresh tissues, contain a red, strongly autofluorescent pigment, possibly condensed tannin derived from the plant (which is lost during tissue preparation), and other phenyl propanoid compounds, which are retained and which may produce the intense reaction of the periodic‐acid‐Schiff's‐positive inner layer. It is concluded that the salivary sheath allows the insects to feed from functioning vessels without embolizing them or losing xylem fluid to the surrounding tissues. These findings and others in the entomological literature indicate low daytime tensions in the xylem conduits of the host plants.
Carbon isotopic composition of legumes with photosynthetic stems from mediterranean and desert habitats
Authors: Nilsen Erik T. , Sharifi M. Rasoul
Published: April 2006

The carbon isotopic compositions of leaves and stems of woody legumes growing in coastal mediterranean and inland desert sites in California were compared. The overall goal was to determine what factors were most associated with the carbon isotope composition of photosynthetic stems in these habitats. The carbon isotope signature (δ13C) of photosynthetic stems was less negative than that of leaves on the same plants by an average of 1.51 ± 0.42 %. The δ13C of bark (cortical chlorenchyma and epidermis) was more negative than that of wood (vascular tissue and pith) from the same plant for all species studied on all dates. Desert woody legumes had a higher δ13C (less negative) and a lower intercellular CO2 concentration (Ci) (for both photosynthetic tissues) than that of woody legumes from mediterranean climate sites. Differences in the δ13C of stems among sites could be entirely accounted for by differences among site air temperatures. Thus, the δ13C composition of stems did not indicate a difference in whole‐plant integrated water use efficiency (WUE) among sites. In contrast, stems on all plants had a lower stem Ci and a higher δ13C than leaves on the same plant, indicating that photosynthetic stems improve long‐term, whole‐plant water use efficiency in a diversity of species.
Why do early‐emerging tree seedlings have survival advantages?: a test using acer rubrum (Aceraceae)
Authors: Jones Robert H. , Allen Bruce P. , Sharitz Rebecca R.
Published: April 2006

In forest understories, tree seedlings that germinate and emerge early in the growing season have significant survival advantages. We hypothesized that (a) early emergence is related to seed size and half‐sib family, and (b) increased survival is due to reduced competition for resources. To test these hypotheses, we collected seeds of Acer rubrum from four half‐sib families and planted them in the understory of a South Carolina floodplain forest. In one experiment, date of emergence was not related to seed size or half‐sib family. However, our method of seed collection may have underestimated variability among half‐sib families. In a second experiment, seeds were spread onto 20 understory plots, half of which were trenched to reduce root competition with overstory trees. One‐year survival and biomass were greater for early‐ than for later‐emerging cohorts. Trenching changed biomass distribution among aboveground parts and may have increased total biomass, but had essentially no impact on survival or root mass. Variation in plot flooding resulted in large differences in timing of emergence, survival, and biomass. For Acer rubrum, the survival advantage accorded by early emergence may be more related to flooding, light conditions, and genetic heterogeneity than to seed size or avoidance of root competition.
Zygotic embryogenesis in Anthurium (Araceae)
Authors: Matsumoto Tracie K. , Kuehnle Adelheid R. , Webb David T.
Published: April 2006

Morphological, anatomical, and histochemical aspects of zygotic embryogenesis by Anthurium andraeanum Lind. were investigated from 4 to 24 wk postpollination. Anatomical features were correlated with morphology of the spadix and capacity of embryos to germinate in vitro. Development from a single‐cell zygote to fully mature seed takes 24 wk. The suspensor was two ranked and obvious during the early stages of embryogeny. It was apparent by week 8, substantial until week 14, and diminished rapidly until its absence by week 22. Differentiation of the shoot apex, cotyledon, and protoderm occurs at 14 wk. The embryo starts to derive nutrition from the endosperm at this time, and germination of cultured ovules reached 56%. By 20 wk the shoot apex had visible leaf primordia and the root apex was clearly defined. The cotyledon was well developed and surrounded the shoot tip. The storage of protein and starch was at its greatest in the endosperm and embryo. Furthermore, 100% germination of cultured ovules and embryos occurred at 20 wk and thereafter. Fully mature embryos at 24 wk are green and contain protoxylem elements.
Sex ratios, size distributions, and sexual dimorphism in the dioecious tree Ilex aquifolium (Aquifoliaceae)
Authors: Obeso Jose´ Ramo´n , Alvarez‐Santullano Manuel , Retuerto Rube´n
Published: April 2006

Sex ratio and sexual dimorphism in physiology and growth were studied in the dioecious tree Ilex aquifolium at two localities in northern Spain. Genet sex ratio was significantly male biased in one locality but not in the other. However, ramet and flowering ramet sex ratios were male biased at both study sites. Males had significantly thicker main trunks than females in one locality and produced more ramets in the other. Growth rate, estimated from mean width of annual rings, did not differ between localities, but males produced wider rings than females at both sites. Mean annual growth rates over the last 10, 20, and 30 yr were significantly higher for males. Measurements of chlorophyll fluorescence indicated that the efficiency of photosynthesis of leaves on nonfruiting branches of females was higher than for leaves on branches of male plants under low‐light conditions, though not under saturating‐light conditions. Efficiency of photosynthesis was significantly lower on fruiting branches of female plants than on nonfruiting branches. We discuss whether the observed between‐sex differences are attributable to the higher cost of reproduction in females and/or to pollen competition.
The effect of timing of pollination on the mating system and fitness ofKalmia latifolia (Ericaceae)
Authors: Levri Maureen A.
Published: April 2006

Plant mating systems are known to vary within species and some immediate ecological factors have been found to be associated with the geographic distribution of selfing. The environmental condition of the maternal plant may influence the production of selfed seed relative to outcrossed seed. This study investigated the effect of late pollination on the mating system of Kalmia latifolia, a long‐lived perennial shrub. A 2 × 2 experimental design was used to determine whether reproductive success declines over the course of the flowering season and whether there was an interaction between pollination time (early vs. late in the season) and pollen type (self‐fertilized vs. outcrossed). An interaction of this sort would indicate context‐dependent fitness of selfed seeds compared to outcrossed seeds and, thus, show an ecological influence over a plant's mating system. Relative fitness was assessed in terms of female reproductive success. Timing of pollination did not affect abortion of outcrossed seeds; however, delay in pollination increased abortion of selfed seeds by 34.7%. Thus, it appears that plants selectively aborted selfed seeds rather than outcrossed seeds and this selection was more intense at the end of the season. An ecological factor such as time of pollination may affect the mating system of K. latifolia.
Fruit set, nectar reward, and rarity in the Orchidaceae
Authors: Neiland Mary Ruth M. , Wilcock Christopher C.
Published: April 2006

A review of comparative levels of reproductive success among nectariferous and nectarless orchids worldwide was compiled from a comprehensive survey of fruit set from 117 orchid species in the literature and from our own field studies. It confirms the hypothesis that nectariferous orchids are more successful in setting fruit than are nectarless species. Overall fruit set figures for nectarless and nectariferous orchids were 19.5 and 49.3% for North America, 27.7 and 63.1% for Europe, 41.4 and 74.4% for the temperate southern hemisphere, and 11.5 and 24.9% for the tropics, demonstrating that the dichotomy is consistent across all geographical areas. On average, the provision of nectar doubles the probability of fruit set in both temperate and tropical areas, but tropical orchids are remarkable in that all (whether nectarless or nectariferous, or terrestrial or epiphytic) display low fruit productivity (<50%). Fruiting failure in the tropics may be balanced by higher productivity per capsule, since tropical orchid fruits contain on average 150 times more seeds than temperate ones. Hybridization occurs more frequently among nectarless orchids in Britain and Europe than among nectariferous ones, and there is a significant positive association between orchid rarity and lack of nectar reward in the British Isles. Sexual reproduction in the Orchidaceae is predominantly pollinator dependent, but this can sometimes be successfully circumvented by asexual seed production (agamospermy) or, more frequently, by automatic self‐pollination (autogamy). The proportion of highly successful nectarless orchids from all geographic areas is very low and comparable with that of orchids offering rewards other than nectar (∼14% of species in each case) emphasizing that high reproductive success is only associated with nectar reward (53% of species). It is suggested that the evolution of nectar production within the family has been the most frequent means of escaping the reproductive limitations of low pollinator visitation frequencies.
Spatial/temporal variations in shrub thicket soil seed banks on an Atlantic Coast barrier island
Authors: Crawford Edward R. , Young Donald R.
Published: April 2006

Potential species replacement within low‐diversity shrub thicket communities was investigated for a Virginia barrier island. Seed bank species composition was quantified in a glasshouse study using soil samples collected beneath closed Myrica cerifera thickets, as well as from thicket gaps. Samples were collected from productive and aging thickets, corresponding to differences in soil age. These data were compared to species presently occurring within the thickets and gaps. Seedbank species composition was not indicative of current community composition for either the intact thickets or the gaps. Seed banks resembled a more pioneer community. Thirteen families, 23 genera, and 25 species were identified from the seed bank beneath the M. cerifera thickets. Four species were woody. The within‐gap seed bank included 19 families, 30 genera, and 34 species. Eight species were woody. The current community included 21 families, 33 genera, and 36 species beneath the intact thickets as well as within the thicket gaps. Eighteen species were woody. The species richness of gaps was more than three times that of intact thickets. For low‐diversity shrub thickets, gaps enhance species richness.
Sporophytes and gametophytes of Dicranaceae from the Santonian (Late Cretaceous) of Georgia, USA
Authors: Konopka Anastasia S. , Herendeen Patrick S. , Crane Peter R.
Published: April 2006

A new species (Campylopodium allonense) of the moss family Dicranaceae is described for fossil sporophyte capsules and associated gametophytes from the late Santonian (Late Cretaceous) Buffalo Creek Member of the Gaillard Formation in central Georgia, USA. The sporophyte capsules are most comparable to those of the living genus Campylopodium. Sporangia are curved, cylindrical, and strumose, with an obliquely rostrate operculum, cucullate calyptra, and compound annulus. The peristome is haplolepidous with 16 dicranoid, apically bifid teeth that are vertically striate on the outer surface and asymmetrically trabeculate on the inner surface. Spores are spherical, alete, and finely rugose, and thus differ from the finely papillose spores of extant Campylopodium. Associated fossil gametophytes are consistent with the morphology of extant Campylopodium and have leaves with a broad sheathing base and a narrow blade. Spores identical to those in the sporangium occur on the leaf surfaces of one of the gametophyte specimens, providing circumstantial evidence that both sporophyte and gametophyte belong to the same species. Inadequacies of the moss fossil record have led to contrasting interpretations of the timing of evolutionary change in this lineage since the Paleozoic. Campylopodium allonense unequivocally provides the earliest evidence of Dicranaceae in the fossil record. This material, along with other fossil mosses from this late Santonian locality, indicates the presence of modern families of mosses in the Cretaceous. In a phylogenetic context, these fossils from two different subclasses imply that mosses were already diverse by the Late Cretaceous.
Isozyme variation in Calliandra calothyrsus (Leguminosae): its implications for species delimitation and conservation
Authors: Chamberlain Joanne R.
Published: April 2006

Patterns of genetic diversity within and among populations of Calliandra calothyrsus, an important multipurpose tree species, were examined using isozyme analysis. C. calothyrsus is a widespread species distributed throughout Central America and southern Mexico, across a variety of environments. Morphologically and ecologically distinct populations can be identified within this range, but they are currently considered to represent a single species. C. calothyrsus has been introduced to many parts of the tropics, where it is cultivated as a source of fuelwood, animal fodder, green manure, and shade by rural communities. Some of these introductions are known to have originated from Guatemala, but very little is known about the genetic diversity of either the native or naturalized populations. Isozyme electrophoresis of 23 loci across 17 populations of C. calothyrsus indicated that the majority of genetic diversity was partitioned between populations (FST = 0.802) and that within‐population heterozygosity was low (mean Ho = 0.057). Naturalized populations had lower than expected heterozygosities and were most similar to material from Santa María de Jesus, a natural population in southern Guatemala. Four distinct groups of populations were identified on the basis of Nei's genetic distances and Population Aggregation Analysis (PAA), and correlate with the morphological and ecological differences that can be observed within the species. The results are discussed in relation to species delimitation and conservation.
Phylogenetic relationships in the Crassulaceae inferred from chloroplast DNA restriction‐site variation
Authors: Van Ham Roeland C. H. J. , Hart Henk ’t
Published: April 2006

A restriction‐site analysis of chloroplast DNA from 44 species, representing 19 genera and all six subfamilies of the Crassulaceae was conducted using 12 restriction endonucleases. A total of 969 variable sites was detected, 608 of which were phylogenetically informative and used in parsimony analysis. Estimated values of nucleotide sequence divergence were used to construct a distance tree by the neighbor‐joining method. Maximum sequence divergence in the family was ~7%. Different tree inference methods yielded only moderately different topologies. The amount of support for the monophyletic groups obtained in the Wagner parsimony analysis was evaluated by bootstrap and decay analysis. There is very strong support for a basal division of the family, which separates the monophyletic subfamily Crassuloideae from all other taxa. Four of the six traditionally recognized subfamilies are indicated to be polyphyletic. These include the Cotyledonoideae, Sempervivoideae, Sedoideae, and Echeverioideae. The Kalanchoideae and the genera Cotyledon and Adromischus exhibit low levels of cpDNA sequence divergence relative to one another, suggesting a relatively recent radiation. The genera Sedum and Rosularia are indicated to be polyphyletic. Sedum comprises sister taxa of most of the other genera of the family.
Class II tassel seed mutations provide evidence for multiple types of inflorescence meristems in maize (Poaceae)
Authors: Irish Erin E.
Published: April 2006

The tassel seed mutations ts4 and Ts6 of maize cause irregular branching in its inflorescences, tassels, and ears, in addition to feminization of the tassel due to the failure to abort pistils. A comparison of the development of mutant and wild‐type tassels and ears using scanning electron microscopy reveals that at least four reproductive meristem types can be identified in maize: the inflorescence meristem, the spikelet pair meristem, the spikelet meristem, and the floret meristem. ts4 and Ts6 mutations affect the fate of specific reproductive meristems in both tassels and ears. ts4 mutants fail to form spikelet meristems from spikelet pair meristems. Ts6 mutants are delayed in the conversion of certain spikelet meristems into floret meristems. Once floret meristems are established in both of these mutants, they form florets that appear normal but fail to undergo pistil abortion in the tassel. The abnormal branching associated with each mutant is suppressed at the base of ears, permitting the formation of normal, fertile spikelets. The classification of the different types of reproductive meristems will be useful in interpretation of gene expression patterns in maize. It also provides a framework for understanding meristem functions that can be varied to diversify inflorescence architectures in the Gramineae.
Cytochalasin D does not inhibit gravitropism in roots
Authors: Staves Mark P. , Wayne Randy , Leopold A. Carl
Published: April 2006

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments. These results indicate that an interaction between amyloplasts and the actin cytoskeleton is not critical for gravity sensing in higher plants and weaken the current statolith hypothesis.
Parental effects on seed mass: seed coat but not embryo/endosperm effects
Authors: Lacey Elizabeth P. , Smith Sara , Case Andrea L.
Published: April 2006

Many biologists studying environmentally induced parental effects have indirectly suggested that the parental environment alters seed mass by altering the amount of endosperm or embryo tissue in the seed. We tested this hypothesis by measuring the effects of parental temperature on total seed mass, seed coat mass, and embryo/endosperm mass in offspring of Plantago lanceolata. Parental temperature significantly affected total seed and coat mass but not endosperm/embryo mass. Thus, larger seeds do not contain more resources in the embryo or endosperm than do small seeds. Rather they have more coat mass, which probably strongly influences germination. These results suggest caution when making assumptions about the pathways by which environmentally induced parental effects are transmitted in plant species. We also observed that controlled crosses differed significantly in their response to parental temperature, which provides evidence for genetic variation in environmentally induced parental effects, i.e., intergenerational phenotypic plasticity, in natural populations of P. lanceolata.
Variation in allozymes and stomatal size in pinyon (Pinus edulis, Pinaceae), associated with soil moisture
Authors: Mitton Jeffry B. , Grant Michael C. , Yoshino Ayako Murayama
Published: April 2006

Microgeographic allozyme variation was examined in pinyon pine, Pinus edulis, among five collection sites in Owl Canyon, Colorado. Relatively dry and moist sites were identified by associated plant communities and the sizes and densities of trees. Three moist sites and two dry sites were compared, and because all sites were within 600 m of one another, isolation by distance was not considered as a viable explanation of genetic differentiation between sites. Allelic frequencies at glycerate dehydrogenase (Gly) differed by 14% between moist and dry areas, and the pattern of microgeographic variation found here—allele 3 higher in frequency on dry sites—was consistent with previous studies of microgeographic variation in contrasting moist and dry sites. Trees within one of the dry sites were examined to test the hypothesis that stomata sizes and densities are heterogeneous among Gly genotypes. Heterozygotes had the longest and widest stomata; the stomatal area of heterozygotes was 28% greater than the stomatal area of homozygotes. Whereas the stomatal areas of the two homozygotes were similar, their shapes did not overlap when projected on a bivariate plot of length and width. These results suggest that stomatal shape may play a role in adapting pinyon to heterogeneity in soil moisture.