bluuebunny/crossref_metadata_2025 huggingface dataset:
AUTOPOLYPLOIDY IN HEUCHERA MICRANTHA (SAXIFRAGACEAE)
Authors: Ness Bryan D. , Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

Heuchera micrantha (Saxifragaceae) is a morphologically variable species comprising five varieties: diversifolia, erubescens, hartwegii, micrantha, and pacifica. Both diploids (2n = 14) and tetraploids (2n = 28) occur within the species. The tetraploid cytotype occupies the central portion of the geographic range of the species, whereas diploids occur primarily in the southern and northern portions of the range. Both diploids and tetraploids have been detected within vars. diversifolia, pacifica, and hartwegii. All counts for vars. erubescens and micrantha are diploid and tetraploid, respectively. Several lines of evidence suggest that tetraploid H. micrantha is of autopolyploid origin. The species is distinct morphologically and is also well separated geographically from other closely related species in subsection Micranthae. The two cytotypes are karyologically identical, possess nearly the same suite of allozymes, and have a very high genetic identity (Ī = 0.971). Significantly, an earlier study documented tetrasomic inheritance in the tetraploid cytotype. Following theoretical expectations, the mean number of alleles per locus, proportion of loci that are polymorphic, and observed heterozygosity are significantly higher for the autotetraploid than for the diploid. The occurrence of both cytotypes in three of the varieties suggests that autopolyploidy may have occurred several times independently in H. micrantha. This was further substantiated by discriminant analysis using morphological characters, which provided evidence for a minimum of two separate origins for the autopolyploid cytotype.
EVOLUTIONARY AND GEOGRAPHIC TRENDS IN ADAPTIVE WOOD ANATOMY IN ERIASTRUM DENSIFOLIUM (POLEMONIACEAE)
Authors: Patterson Robert , Tanowitz Barry D.
Published: January 2018

Anatomical features of Eriastrum densifolium populations in southern California show variation that correlates well with ecological setting and geographical distribution. Vessel element size and density in shoots suggest strong adaptation among different subspecies to efficient water movement in different habitats. Indices of mesomorphy, devised by Carlquist to indicate relative adaptivity of wood, likewise show considerable variation among populations, suggesting that different subspecies have anatomical components that can define them. Relationships among the five subspecies of E. densifolium may be explored through MI value relationships.
DEVELOPMENT OF THE PHYTOMELANIN LAYER IN FRUITS OF AGERATUM CONYZOIDES (COMPOSITAE)
Authors: Pandey Arun K. , Wilcox Lee W. , Sack Fred D. , Stuessy Tod F.
Published: January 2018

The development of the phytomelanin layer in the achenes of Ageratum conyzoides (Compositae, Eupatorieae) was studied using light and electron microscopy. At the level of the embryo sac, the young ovary wall contains an outer zone, consisting of an epidermis and two hypodermal layers, and an inner zone, consisting of developing fiber cells and 3–5 layers of parenchyma. A schizogenous space forms between the developing fibers and the inner hypodermis at about the time that the embryo sac is fully organized. At this stage, the developing fibers contain papilla which are outgrowths that connect the fibers to the inner hypodermal cells. After fertilization, phytomelanin accumulates on the cell walls lining this space. Subsequently, by the time the fruit matures, the phytomelanin fills the space completely and forms a solid, black layer. The surface of the inner hypodermis that faces the space forms a mold; the characteristic peglike projections of the mature phytomelanin layer develop by filling the invaginations between the hypodermal cells. During phytomelanin accumulation, abundant smooth endoplasmic reticulum is present in the hypodermis, especially in the outer layer. It is hypothesized that the precursors of the phytomelanin are synthesized in this endoplasmic reticulum and that these precursors migrate into the space where the phytomelanin is polymerized.
CLONAL STRUCTURE OF ARCTIC DWARF BIRCH (BETULA GLANDULOSA) AT ITS NORTHERN LIMIT
Authors: Hermanutz L. A. , Innes D. J. , Weis I. M.
Published: January 2018

Betula glandulosa Michx. (Betulaceae) at Tarr Inlet, Baffin Island, Northwest Territories reproduces primarily by vegetative layering with little, if any, viable seed production or seedling recruitment. Information from polymorphic enzyme loci revealed 15 three‐locus genotypes with a single genotype usually dominating each of the nine sampled sites. Clonal reproduction combined with self‐incompatibility may be one factor contributing to a decreased seed set by reducing the probability of xenogamy. However, multiple genotypes were found at some sites providing an opportunity for cross compatible pollen to effect fertilization. The lack of seed set in these areas appears to be due to additional factors inhibiting sexual reproduction. Based on pollen records, the present limited distribution of Betula glandulosa on Baffin Island represents the remnants of once more widely distributed populations, and the failure of sexual reproduction at the northern edge of its range may be responsible for the decline in abundance. Genotypic diversity observed in the Tarr Inlet area appears to be residual from a once sexually reproducing population. No evidence was found for differential selection of genotypes indicating that random processes are probably eroding the genotypic diversity during the decrease of population size in this species.
EFFECTS OF WATER DEPTH ON TYPHA LATIFOLIA AND TYPHA DOMINGENSIS
Authors: Grace James B.
Published: January 2018

The two species of Typha common in the southeastern United States, T. latifolia and T. domingensis differ substantially in their tolerance to deep water. The objective of this study was to examine the morphology and biomass allocation of these two species to determine if they have similar phenotypic responses to water depth. Replicate monocultures of the two species were established at a range of water depths in an artificial pond and allowed to grow for three growing seasons. At the end of the experiment, subsamples were harvested for determination of plant morphology as well as above‐ and belowground biomass.

Both species of Typha showed increases in maximum height with increasing depth. The species less tolerant to deep water (T. latifolia) allocated more of its biomass to leaves with increasing water depth. In contrast, the deep water species (T. domingensis) showed increased total size of each ramet but a fixed percentage of biomass in leaves with increasing water depth. Both species had a decreasing incidence of flowering and decreasing shoot density with increasing water depth. In general, these species conform to expectations based on considerations of how their carbon budgets would be affected by water depth.
GEOGRAPHICAL DISTRIBUTION OF B CHROMOSOMES OF XANTHISMA TEXANUM (COMPOSITAE: ASTEREAE). II. LOCAL VARIATION WITHIN AND BETWEEN POPULATIONS AND FREQUENCY VARIATION THROUGH TIME
Authors: Semple John C.
Published: January 2018

Variation in the frequency of individuals of Xanthisma texanum with B chromosomes among populations at the local level and variation in the frequency and distribution through time of individuals with B chromosomes within populations was investigated in a small area of southwestern Oklahoma and adjacent Texas between 1974 and 1987. The chromosome numbers of 1,224 individuals were determined from meiotic material; 15.8% of these had B chromosomes, less than 1% had three or four B chromosomes; none had more than four B chromosomes. The frequency of plants with B chromosomes among all sites sampled ranged from 0 to 33% and from 0 to 25% in sites separated by only a hundred meters; large differences in sample size occurred. Even at the subsite level large differences in frequencies in plants with B chromosomes were found. Within single sites, B chromosome frequency was not constant through time: the pattern of change differed among subsites within populations. In some cases the frequency went to zero. No correlations between environmental parameters and B chromosome frequency were documented.
FLORAL DEVELOPMENT IN GYMNOTHECA CHINENSIS (SAURURACEAE)
Authors: Han‐Xing Liang , Tucker Shirley C.
Published: January 2018

The development of the inflorescence and flowers are described for Gymnotheca chinensis Decaisne (Saururaceae), which is native only to southeast China. The inflorescence is a short terminal spike of about 50–70 flowers, each subtended by a small bract. There are no showy involucral bracts. The bracts are initiated before the flowers, in acropetal order. Flowers tend to be initiated in whorls of three which alternate with the previous whorl members. No perianth is present. The flower contains six stamens, and four carpels fused in an inferior ovary containing 40–60 ovules on four parietal placentae. Floral symmetry is dorsiventral from inception and throughout organ initiation. Floral organs are initiated in the following order: 1) median adaxial stamen, 2) a pair of lateral common primordia which bifurcate radially to produce two stamen primordia each, 3) median abaxial stamen, 4) a pair of lateral carpel primordia, 5) median adaxial carpel, 6) median abaxial carpel. This order of initiation differs from that of any other Saururaceae previously investigated. The inferior ovary results from intercalary growth below the level of stamen attachment; the style elongates by intercalary growth, and the four stigmas remain free. The floral structure of Gymnotheca is relatively advanced compared to Saururus, but its assemblage of specializations differs from that of either Anemopsis or Houttuynia, the other derived genera in the Saururaceae.
6(5)CARBOXYFLUORESCEIN AS A TRACER OF PHLOEM SAP TRANSLOCATION
Authors: Grignon Nicole , Touraine Bruno , Durand Monique
Published: January 2018

6(5)carboxyfluorescein (6(5)CF), a polar fluorescein with an apparent pK of 6.3, was introduced, as a pH 6.3 solution, into the apoplast of lamina or petioles of mature soybean leaves. Freehand sections were prepared at various times and immediately observed with a fluorescence microscope. 6(5)CF‐associated fluorescence appeared in all sink organs, from shoot apex to roots. It was strictly confined to the phloem regions, even after 4 days. Its transport into young leaves ceased at approximately the time they underwent sink‐to‐source transition. It was never transported between two leaflets of the same leaf. Its transport was interrupted by phloem destruction. All these transport characteristics were highly reproducible, and were paralleled by those of 14C transport after application of (14C)sucrose to leaf surfaces. In contrast with 6(5)CF, fluorescein was transported between mature leaves, and between leaflets of the same leaf. It was not restricted to phloem, and often appeared in the xylem region. These results indicate that 6(5)CF can be used to monitor phloem sap translocation in real time, in short‐ and long‐term experiments.
PATTERNS OF LEAF AND FLOWER REMOVAL: THEIR EFFECT ON FRUIT GROWTH IN CHAMAENERION ANGUSTIFOLIUM (FIREWEED)
Authors: Shea Margaret M. , Watson Maxine A.
Published: January 2018

The response of Chamaenerion angustifolium (fireweed) plants to different patterns of artificial leaf and flower herbivory was examined to determine if the effects of localized herbivory were confined within vertical sectors of the plant. The effect of leaf and flower removal on fruit development was compared for removals within sectors and distributed among sectors. Fruit development did not differ in plants subjected to different patterns of leaf and flower removal. These results suggest that in disturbed plants carbohydrate movement is not confined within vertical sectors.
VARIATION AMONG POPULATIONS OF XANTHIUM STRUMARIUM (COMPOSITAE) FROM NATURAL AND RUDERAL HABITATS
Authors: Blais Pierre Alain , Lechowicz Martin J.
Published: January 2018

We assessed the mechanisms underlying the ability of cocklebur to spread from its natural riverside habitats and establish weedy populations in urban waste areas. We collected fruits from plants growing in natural and urban ruderal habitats and planted 2 maternal families from each of 9 habitat populations in 3 experimental gardens. The gardens were all in full sunlight but differed in the availability of water and nutrient resources. Plant performance in the gardens was measured by numbers and size of fruits produced. Traits known to be associated with cocklebur reproductive success were also measured: times to emergence and anthesis, photosynthetic capacity, mean stomatal conductance, relative growth rate, and biomass allocation to leaves and stems.

Although there were significant differences among populations in the tradeoff between rate of growth in height and timing of anthesis, these population differences were not associated with habitat. Apart from a tendency to produce larger fruits in ruderal populations, there were no detectable differences in the characteristics of plants from natural vs. ruderal habitats. Plants from both habitats did have substantial and significant plastic responses to growth environment. In the three experimental gardens, fruit numbers increased with resource availability but fruit size did not differ significantly. As resource availability increased, plants from both habitats sustained growth longer and became more branchy. Canonical discriminant analysis of all the somatic and reproductive traits together supported the idea that natural and ruderal populations do differ in their overall plastic response to resource availability. The subtly different plastic responses of plants from the two habitats do not arise by substantial adjustments in a few dominant traits, but instead by relatively minor adjustments in a host of functionally interrelated phenological, morphological, and physiological traits. It is these small but coordinated differences in the plastic responses of many traits that appear to differentiate cocklebur from natural vs. weedy urban habitats.
STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. IV. TRIASSIC OVULES
Authors: Perovich Nancy E. , Taylor Edith L.
Published: January 2018

Small, anatomically preserved ovules are described from specimens collected at Fremouw Peak in the central Transantarctic Mountains. The ovules occur within a silicified peat in the upper part of the Fremouw Formation, which is considered to be Early to Middle Triassic. Ovules are radially symmetrical and ovoid, with an integument that consists of a narrow endotesta and a complex sclerotesta. The bilayered nucellus has a characteristic scalloped appearance and is attached to the integument only at the base. Of 43 ovules examined, 50 to 60% contain cellular megagametophyte tissue. One specimen contains a possible archegonium with embryo. Although the ovules have not been found attached, their possible affinities are discussed in relation to the known flora from this locality and other, comparable‐aged floras from Gondwana.
POLYACETYLENE RESERVOIR (DUCT) DEVELOPMENT IN AMBROSIA TRIFIDA (ASTERACEAE) STAMINATE FLOWERS
Authors: Lersten Nels R. , Curtis John D.
Published: January 2018

Mature staminate flowers of giant ragweed (Ambrosia trifida L.; Asteraceae, tribe Heliantheae) are about 2 mm long. Each of the five fused petals is traversed for most of its length by a prominent polyacetylene‐filled reservoir (PAR). PAR'S have a biseriate epithelium and, except for their short length of about 1.5 mm, seem identical to the much longer PAR's of leaf and stem. Study of sections of resin‐embedded flowers at different developmental stages showed that corolla PAR's appear with a full complement of epithelial cells, and occupy their full relative length, in flowers only 150 μm in length. As the flower enlarges, the original epithelial cells also enlarge and elongate, and secrete into the lumen, which opens simultaneously for its entire length when the flower is nearly 300 μm long. PAR's in mature flowers have only their original epithelial cells, which remain alive. Corolla PAR's seem anatomically to be representative of the canals and ducts that have been described elsewhere in Asteraceae.
CHARACTERIZATION OF MUCILAGE ON THE PROXIMAL CELLS OF YOUNG GAMETOPHYTES OF BOTRYCHIUM DISSECTUM (OPHIOGLOSSACEAE)
Authors: Melan Melissa A. , Whittier Dean P.
Published: January 2018

Young gametophytes of Botrychium dissectum produce a mucopolysaccharide coating on the external surface of the proximal cell. Scanning electron microscopy reveals deposition of the mucilage, which initially has a patchy distribution, in the shape of a thick triangular ring. Young gametophytes in the hydrated condition have a thin coating of mucilage over the other areas of the proximal cell wall. Histochemical staining indicates that the mucilage contains sugars with vicinal hydroxyl groups, carboxylated sugars, and small amounts of sulfated sugars. Protein and phenolic materials are also found in the mucilage. Lipids, β, 1‐3 glucans and β,1‐4 glucans are not present. Fluorescein labelled lectin binding shows the presence of terminal galactose and terminal fucose units. Germinating spores in the presence of the microtubule inhibitors CIPC (3‐chloro‐N‐phenyl isporopyl carbamate) and griesiofulvin cause abnormal mucilage secretion. The inhibitor CIPC prevents mucilage secretion whereas griesiofulvin disrupts the pattern of deposition. Several functions of the mucilage are postulated.
EXPERIMENTAL STUDIES IN PONDEROSA PINE. I. RELATIONSHIP BETWEEN VARIATION IN PROTEINS AND MORPHOLOGY
Authors: Linhart Yan B. , Grant Michael C. , Montazer Parveen
Published: January 2018

Ponderosa pine from California (Pinus ponderosa var. ponderosa) were crossed to one another and also to individuals from the Rocky Mountains (P. p. var. scopulorum). All crosses involved a single mother and a single pollen donor. Patterns of inheritance of electrophoretically‐detectable loci followed Mendelian expectations with one exception. Shikimate dehydrogenase showed unpredictable banding patterns in intervarietal crosses. Variability at these biochemical loci was compared to variability at 14 morphometric characters. The relationship between these two levels of variation is complex and permits only one generalization: variability at one level is not a good predictor of variability at the other level.
SEED GERMINATION ECOPHYSIOLOGY OF JEFFERSONIA DIPHYLLA, A PERENNIAL HERB OF MESIC DECIDUOUS FORESTS
Authors: Baskin Jerry M. , Baskin Carol C.
Published: January 2018

Freshly‐matured seeds of the mesic deciduous woodland herb Jeffersonia diphylla (L.) Pers. (Berberidaceae) have underdeveloped (ca. 0.6 mm in length) embryos and exhibit deep, simple morphophysiological dormancy (MPD). For rapid growth of the embryos at October (20/10) and November (15/6 C) temperatures in October and November, seeds must first be exposed to high (30/15 C) summer temperatures. If embryo growth is not completed in autumn, it continues during winter. However, even after 10–12 weeks at summer temperatures, embryos grew very little at 5 C, unless growth already had begun at autumn temperatures. After embryo growth has been completed, or after it has been initiated, seeds require cold stratification (5 C) to overcome dormancy. Embryos must attain a minimum length of about 1 mm before seed dormancy can be broken by cold stratification. Gibberellic acid increased the rate of embryo growth in seeds kept at 20 C, but only 1–9% of them germinated. Thus, GA substitutes for warm but not cold stratification. High summer temperatures, as well as the traditionally‐used autumn and winter temperatures, should be used in germinating seeds with deep, simple MPD.
STRUCTURALLY PRESERVED LEAVES OF HARRIMANELLA HYPNOIDES (ERICACEAE): PALEOECOLOGY OF A NEW NORTH AMERICAN LATE PLEISTOCENE FOSSIL
Authors: Miller Norton G.
Published: January 2018

Plant macrofossils from the basal inorganic sediments at Tom Swamp, north central Massachusetts, contained leaves, seeds, and fruits of arctic‐alpine species, nearly all of which occur at present near the summits of Mt. Washington and Mt. Katahdin (New England) and in other alpine and arctic areas northward in eastern North America. Included were the needle‐leaves of the dwarf shrub, Harrimanella hypnoides (L.) Coville, which matched comparative modern leaf samples in all anatomical details. The macrofossil assemblage was deposited before 12,830 ± 120 radiocarbon years ago and prior to the expansion of spruce populations in the region. Fossils of H. hypnoides suggest that snow beds were a regular feature of the summer landscape of southern New England during late glacial time. Calculations using the average lapse rate indicate that the mean annual paleotemperature in the Tom Swamp area may have been depressed 8–9 C below present means.
POPULATION GENETIC STRUCTURE IN CHEILANTHES GRACILLIMA
Authors: Soltis Pamela S. , Soltis Douglas E. , Ness Bryan D.
Published: January 2018

Population genetic structure was examined in five populations of the xerically adapted homosporous fern Cheilanthes gracillima. F statistics using allozymic data indicated substantial genetic structure in all populations. To determine the factors responsible for genetic structure, we calculated levels of intragametophytic selfing and the fixation index for each subpopulation of each population and estimated levels of intrapopulational gene flow in each population. These analyses indicated that each subpopulation was a panmictic unit; thus, population genetic structure is not due to family structure, arising via matings between relatives. Intrapopulational gene flow was surprisingly low, given the typically high dispersibility of fern spores. However, it seems unlikely that spore dispersal in C. gracillima is significantly reduced relative to other homosporous ferns. Instead, we propose that the low rates of intrapopulational gene flow reflect limited availability of safesites for spore germination and gametophyte establishment. This ecological factor may play a primary role in generating and/or maintaining population genetic structure in C. gracillima.
GENETIC DIVERSITY IN A CLONAL NARROW ENDEMIC, ERYTHRONIUM PROPULLANS, AND IN ITS WIDESPREAD PROGENITOR, ERYTHRONIUM ALBIDUM
Authors: Pleasants John M. , Wendel Jonathan F.
Published: January 2018

Erythronium propullans is a narrow endemic restricted to two counties in southeastern Minnesota. It coexists at all sites with the widespread common white trout lily, E. albidum. Erythronium albidum has both sexual and asexual reproduction; it has been suggested that E. propullans reproduces strictly by vegetative means. Electrophoretic analysis of 15 enzyme systems encoded by a minimum of 37 genetic loci revealed considerable genetic variation within and among E. propullans populations. However, all measures of variability calculated from allozyme data demonstrate that E. propullans maintains lower levels of genetic variation than E. albidum. There is also evidence for limited gene flow among E. propullans populations, whereas all E. albidum populations are genetically similar. Clonal diversity is also lower in E. propullans. Only 21 clones were found in 100 individuals sampled whereas virtually every one of the 70 individuals of E. albidum sampled had a unique multilocus genotype. The clones of E. propullans cluster into 3 genetically dissimilar groups; variation within each cluster indicates that some sexual recombination does occur. We discuss the effects of clonality and endemism on genetic variation, reasons why the clonal habit might preserve genetic variation, and suggest that the lower variability in E. propullans is due primarily to the genetic bottleneck it experienced at the time of its origin. Isozyme data suggest that E. propullans is a derivative of E. albidum. Based on the degree of genetic similarity and information on the glacial history of the region, we suggest that E. propullans is a local derivative of E. albidum, having arisen no more than 9,000 years ago.
XYLEM STRUCTURE AND ECOLOGICAL DOMINANCE IN A FOREST COMMUNITY
Authors: Guthrie Roland L.
Published: January 2018

The relative dominance of deciduous trees having diffuse, semiring, or ring porous xylem is considered in relation to percent slope, site, vertical stratification within site, and to disturbance. Xylem type relative dominance was calculated on the basis of basal area by a procedure that is generally employed for the determination of species relative dominance. The study area was located within the central hardwoods region of the Eastern Deciduous Forest. On a moisture gradient, the sites were a hydric floodplain, a mesic river terrace and cove, and a xeric hillside spur. There was an increase from lowland to upland sites in absolute number of species having diffuse porous and those having ring porous xylem; however, the data showed no significant difference among the four sites or between the cove's northwest and southwest aspects in the percentages of species having diffuse porous xylem and those having ring porous xylem. In contrast to species number data, relative dominance data showed that diffuse porous species were dominant on the floodplain, on the northwest aspect of the cove, and in lower strata beneath the dominant ring porous upper canopy on the spur and southwest aspect of the cove. Ring porous species were dominant in the upper canopy only on the spur and on the southwest aspect of the cove. Semiring porous species had a high dominance level on the disturbed terrace site, a much lower level of dominance on the less disturbed floodplain, and very low dominance on the relatively undisturbed cove and spur sites. The results demonstrated that sets of closely and distantly related tree species having the same xylem anatomy share some common ecological characteristics, suggesting that xylem structure is a critical character in the adaptation of trees to variations in the environment over small geographical areas.
GRAZING HISTORY, DEFOLIATION, AND FREQUENCY‐DEPENDENT COMPETITION: EFFECTS ON TWO NORTH AMERICAN GRASSES
Authors: Painter Elizabeth L. , Detling James K. , Steingraeber David A.
Published: January 2018

Agropyron smithii and Bouteloua gracilis plants from intensively grazed prairie dog colonies and from a grazing exclosure in Wind Cave National Park, South Dakota, were used to compare responses of conspecific populations with different histories of exposure to grazing and to competition for light. In separate experiments for each species, plants grown in monocultures and two‐population replacement‐series mixtures were used to examine effects of defoliation, frequency‐dependent competition, and population on biomass and morphology.

Colony and exclosure plants frequently responded differently. Defoliation more often adversely affected exclosure plants than colony plants, while interpopulation competition more often adversely affected colony plants. Defoliation frequently negated the competitive advantage of exclosure plants. Intrapopulation competition appeared to be greater among exclosure than colony plants. Our results indicate that conclusions based on studies of plants in long‐term exclosures may not apply to plant populations having long histories of intensive grazing. While there were differences between species, in both, these experiments provide evidence of population differentiation, resulting in morphologically dissimilar populations which responded differently to defoliation and to inter‐ and intrapopulation competition.
SIEVE‐PORE DEVELOPMENT IN SOME LEPTOSPORANGIATE FERNS
Authors: Evert Ray F. , Warmbrodt Robert D. , Eichhorn Susan E.
Published: January 2018

Sieve‐pore development was examined in four species of leptosporangiate ferns: Phlebodium aureum, Platycerium bifurcatum, Pityrogramma calomelanos, and Regnellidium diphyllum. In all four species, sieve‐pore development is initiated with the formation of a barrel‐shaped periplasmodesmatal region—bounded by a narrow, electron‐dense band—around the prepore plasmodesma. This phase is followed by the deposition of callose, or of a calloselike substance, around the prepore plasmodesma. With deposition of this substance, the periplasmodesmatal region is no longer discernible, but an electron‐dense band continues to border the pore site. Perforation of the pore site involves removal of the calloselike substance and widening of the plasmodesmatal canal, both processes occurring more or less uniformly along the entire length of the pore site. During widening of the plasmodesmatal canal, numerous membranous elements appear within the pore. The number of membranous elements within the pore appears to decrease with increasing age of the sieve element. The location of feeding aphid (Myzus persicae) mouth‐parts indicates that the conducting sieve elements in Pellaea viridis are mature cells interconnected by membrane‐containing, callose‐free sieve pores.
CECROPSIS LUCULENTUM GEN. ET SP. NOV.: EVIDENCE FOR HETEROSPOROUS PROGYMNOSPERMS IN THE UPPER PENNSYLVANIAN OF NORTH AMERICA
Authors: Stubblefield Sara P. , Rothwell Gar W.
Published: January 2018

An anatomically preserved specimen of a woody, heterosporous pteridophyte has been discovered in Upper Pennsylvanian peat‐forming swamp deposits of eastern Ohio. The fossil is described as Cecropsis luculentum gen. et sp. nov. It consists of a protostelic shoot tip with helically‐arranged vegetative leaves, sporophylls and adaxial eusporangia. The stele is marginally mesarch, with five cauline protoxylem strands that produce leaf‐trace protoxylem in a helix that approaches 2/5. Dense wood surrounds the protostele. Secondary tracheids have reticulate bordered pitting on all walls. Rays are uniseriate and 1–2 cells high. Vegetative leaves are 2–3 cm long and are pinnately‐dichotomously branched into terete lobes. Sporophylls are somewhat more extensively webbed, with clusters of sporangia located above vascularized receptacles. Sporangia are sessile and globose, with a terminal dehiscence slit. Megasporangia and microsporangia appear to be intermixed. Most are empty, but a small number contain either fragments of bean‐shaped microspores with asymmetrical trilete sutures, or a single radial and trilete megaspore. The presence of gymnospermous protoxylem architecture and wood in this heterosporous pteridophyte place it within the circumscription of the Progymnospermopsida. However, features of the stele, leaves, sporangia, and extreme heterospory indicate that it does not conform to a presently recognized order. The Pennsylvanian occurrence and unique features of Cecropsis leave open to question whether it is phylogenetically, or only phenetically related to other members of the Progymnospermopsida.
TISSUE CULTURE AND REGENERATION OF DISTICHLIS SPICATA (GRAMINEAE)
Authors: Straub Peter F. , Decker Debra M. , Gallagher John L.
Published: January 2018

Distichlis spicata tissue cultures were initiated from mature seeds. Cultures displayed regenerable callus that was compact, white, and streaked with purple and green. Selection of compact areas at subculture established long‐term, regenerable cultures. Removal of auxin and inclusion of 1 mg 1–1 BA in the maintenance media induced regeneration. Histological sections indicate that although cells were typical of embryogenic types, regeneration was by shoot organogenesis. Regenerated plants flowered and set seed under field conditions.
TEMPERATURE, WATER AVAILABILITY, AND NUTRIENT LEVELS AT VARIOUS SOIL DEPTHS‐CONSEQUENCES FOR SHALLOW‐ROOTED DESERT SUCCULENTS, INCLUDING NURSE PLANT EFFECTS
Authors: Nobel Park S.
Published: January 2018

Soil conditions were evaluated over the rooting depths for Agave deserti and Ferocactus acanthodes from the northwestern Sonoran Desert. These succulents have mean root depths of only 10 cm when adults and an even shallower distribution when seedlings, which often occur in association with the nurse plant Hilaria rigida, which also has shallow roots. Maximum soil temperatures in the 2 cm beneath bare ground were predicted to exceed 65 C, which is lethal to the roots of A. deserti and F. acanthodes, whereas H. rigida reduced the maximum surface temperatures by over 10 C, providing a microhabitat suitable for seedling establishment. Water Availability was defined as the soil‐to‐plant drop in water potential, for periods when the plants could take up water, integrated over time. Below 4 cm under bare ground, simulated Water Availability increased slightly with depth (to 35 cm) for a wet year, was fairly constant for an average year, and decreased for a dry year, indicating that the shallow rooting habit is more advantageous in drier years. Water uptake by H. rigida substantially reduced Water Availability for seedlings associated with this nurse plant. On the other hand, a 66–90% higher soil nitrogen level occurred under H. rigida, possibly representing its harvesting of this macronutrient from a wide ground area. Phosphorus was slightly less abundant in the soil under H. rigida compared with under bare ground, the potassium level was substantially higher, and the sodium level was substantially lower. All four elements varied greatly with depth, N and K decreasing and P and Na increasing. Based on the known growth responses of A. deserti and F. acanthodes to these four elements, growth was predicted to be higher for plants in soil from the shallower layers, most of the differences being due to nitrogen.
TRANSLOCATION IN THE NONPOLYTRICHACEOUS MOSS GRIMMIA LAEVIGATA
Authors: Alpert Peter
Published: January 2018

A superficially rhizomatous habit suggested that the moss Grimmia laevigata might function as a clonal, rhizomatous plant and translocate photoassimilates to belowground organs, even though the species is outside the order Polytrichales, which includes the only mosses known to possess sieve cells. Labelling with 14CO2 indicated that at least 10% of newly assimilated carbon was translocated out of leafy shoot portions within 26 hr. Of this carbon, approximately 75% was apparently moved into leafless, basal shoot portions and 25% into belowground stems. Infrared gas analysis of net CO2 flux was used to check that labelling gave a realistic measure of photosynthesis. Physiological integration and clonal spread may account for the unusual ability of this moss to colonize extremely xeric microsites.
CHROMOSOME NUMBERS IN CUPHEA (LYTHRACEAE): NEW COUNTS AND A SUMMARY
Authors: Graham Shirley A.
Published: January 2018

The American genus Cuphea with ca. 260 species is extremely diverse with respect to chromosome number. Counts are now available for 78 species and/or varieties, or 29% of the genus. Included in this study are first reports for 15 taxa from Brazil, Cuba, Dominican Republic, Mexico, and Venezuela. Twenty‐two different numbers are known for the genus, ranging from n = 6 to n = 54. The most common number in the primary center of species diversity in Brazil is n = 8, which is regarded as the base number of the genus. Two numbers are most common in the secondary center in Mexico, n = 10 and n = 12. Species with n = 14 or higher are considered to be of polyploid origin. Polyploids comprise 46% of the total species counted and appear in 9 of the 11 sections for which chromosome numbers have been reported. Aneuploid species comprise ca. 25% of the genus and are known from 7 of the 11 sections. The two subgenera are not characterized by different chromosome numbers or sequences of numbers. None of the 14 sections are circumscribed by a single chromosome number. Morphological and ecological variability in widespread, weedy species is correlated with differing chromosome numbers in some species whereas in others the chromosome number is stable. Summary of chromosome numbers by taxonomic section is presented. Section Euandra, centered in eastern Brazil, and the largest section of the genus, appears to be chromosomally most diverse. In section Trispermum, characterized by difficult, variable species with intermediate forms, two of the four species studied have polyploid races. Section Heterodon, endemic to Mexico and Central America and comprising most of the annual species of the genus, is best known chromosomally. Chromosome numbers have been counted for 25 of 28 species, and 12 different numbers are reported. The most advanced sections, Melvilla and Diploptychia, with numerous species occurring at higher altitudes, are characterized by high polyploids. Apomictic species occur in sect. Diploptycia. The cytoevolution of Cuphea is complex with frequent polyploid and aneuploid events apparently playing a significant role in speciation in both centers of diversity.
REGIONS OF CELL DIVISION AND ELONGATION DURING STEM GROWTH OF XANTHIUM
Authors: Maksymowych Roman , Orkwiszewski Joseph A. J. , Maksymowych Andrew B.
Published: January 2018

Regions of cell division and cell elongation were established during stem growth of Xanthium pensylvanicum (cocklebur). From percent mitosis it was determined that the region of cell division in a Xanthium stem of Plastochron Index (PI) 13.89 was 20 mm long, starting from the stem apex and proceeding in a basipetal direction. Measurements of cortical cell lengths demonstrated that mature cell length in the stem of the same plant was reached at about 55 mm distance from the stem apex. Between 20 and 55 mm distance from the apex, shoot growth occurred by cell elongation alone. The maximum rate of change in cell length (dC/dX) was at about 15 mm distance from the stem apex. The length of the apical growth region was a function of the age of the plants. The older the plant, the longer its apical region of elongation. Growth of Xanthium stems was due primarily to elongation of internodes; the nodal regions did not seem to elongate.
WIND POLLINATION, SELF‐INCOMPATIBILITY, AND ALTITUDINAL SHIFTS IN POLLINATION SYSTEMS IN THE HIGH ANDEAN GENUS ESPELETIA (ASTERACEAE)
Authors: Berry Paul E. , Calvo Ricardo N.
Published: January 2018

Altitudinal changes in breeding and pollination systems of tropical montane plants were studied in 13 species of Espeletia growing in the Venezuelan Andes from 2,000 to 4,300 m. Hand pollination tests showed that all species were strongly self‐incompatible. The four species found only above 4,000 m had up to 10% median seed set in self‐pollinated heads, which was significantly higher than the lower elevation species. Nine species were insect‐pollinated, with large bees the major pollinator group. An endemic páramo hummingbird, Oxypogon guerinii, was an important visitor of E. schultzii in three populations examined. Experimental bagging experiments showed that the four high elevation species were wind‐pollinated, further evidenced by the lack of pollinator visits and markedly different capitulum morphologies. Open‐pollinated seed set in two wind‐pollinated species, E. spicata and E. timotensis, was strongly dependent on the population's flowering density, which varied significantly from year to year. The shift from insect to wind pollination in Espeletia can be related to the low pollinator availability at high elevations in the Andes, protection of the capitula from snow and daily frosts, and the extremely long flowering periods of individual heads.
EPIDERMIS AND HYPODERMIS OF THE SAGUARO CACTUS (CEREUS GIGANTEUS): ANATOMY AND SPECTRAL PROPERTIES
Authors: Darling M. S.
Published: January 2018

The epidermis and hypodermis (E‐H) in the saguaro cactus (Cereus giganteus Engelm.) comprise a relatively stiff, thick structure of 10 cell layers, with long substomatal canals. This structure, together with the chlorenchyma, forms a system that protects the chlorenchyma from ultraviolet‐alpha and ‐beta (UV‐A and UV‐B) radiation, permits absorption of much of the incident photosynthetically active radiation (PAR), and reduces the heat load on the plant. The major contributions of the E‐H to this system are at the shorter wavelengths: it is virtually opaque to UV radiation, and transmits approximately 68% of PAR and over 80% of near‐infrared (IR). The high reflectance of the chlorenchyma in the near‐IR reduces the absorption by the intact plant to less than 40% of incident radiation.
EFFECTS OF SULFIDE ON THE GROWTH OF THREE SALT MARSH HALOPHYTES OF THE SOUTHEASTERN UNITED STATES
Authors: Bradley Paul M. , Dunn E. Lloyd
Published: January 2018

A hydroponic culture experiment was performed to ascertain whether sediment soluble sulfide at in situ concentrations plays a role in the determination of height forms of Spartina alterniflora in salt marshes of the United States. Additional experiments were conducted for both Spartina cynosuroides and Borrichia frutescens to determine if sulfide also influences the overall distribution of these species in the marsh. In situ soluble sulfide concentrations ranged from 0.02 mm in creek bank sites up to 3.0 mm in the inner marsh. In culture treatments, both plant height and biomass production of S. alterniflora were inhibited at a sulfide concentration as low as 1.0 mm, strongly suggesting a role for sulfide in the determination of height forms in the marsh. Production of S. cynosuroides was inhibited at high sulfide concentrations. However, over a range of concentrations similar to in situ values, no significant reduction in growth was observed, indicating sulfide was not a primary determinant of growth in stands of S. cynosuroides on Sapelo Island, Georgia. A sulfide concentration of 0.5 mm inhibited production in B. frutescens. In situ sulfide concentrations as high as 0.5 mm were found only in mixed stands of Juncus roemerianus and B. frutescens.
INDUCTION OF ADVENTITIOUS BRANCHES FROM CULTURED CITRUS JUICE VESICLES–A POTENTIAL MEANS OF PROLIFERATION
Authors: Tisserat Brent , Galletta Paul D. , Jones Danny
Published: January 2018

The noncallusing morphogenetic properties of Citrus juice vesicles cultured in vitro are unknown and were herein studied. Juice vesicles isolated from 120–180‐day‐old fruits are capable of proliferation via adventitious vesicle branching in vitro. Gibberellic acid levels of 1–100 mg/L greatly enhanced adventitious vesicle branching while delaying vesicle senescence as evidenced by the vesicles' ability to retain its green color for up to 4 to 6 mo in culture. Vesicles grown on media without gibberellic acid readily matured, turning opaque within 2 mo in culture and rarely produced adventitious branches. Additions of 0.1 mg/L α‐naphthaleneacetic acid or 1.0 mg/L benzylaminopurine to media containing 10 mg/L gibberellic acid further enhanced vesicle branching in some species and cultivars. Adventitious juice vesicles have been induced from a variety of citrus species, including Citrus grandis (L.) Osb., C. hystrix DC., C. limon (L.) Burm. f., C. medica L., C. paradisi Macf., C. reticulata Blanco, and C. sinensis (L.) Osb. Adventitious vesicle branches originate from primordia initiated on the surface of the cultured vesicle. These primordia commonly occurred on the terminal meristem region of the vesicle. However, some species (e.g., C. grandis and C. paradisi) produced adventitious vesicle branches from their bodies and stalks as well. Distinct vesicle branches begin to appear on preformed vesicles after 30–60 days in culture. A survey to determine the natural occurrence of vesicle branching in various Citrus species was also conducted. Natural vesicle branching commonly occurred in C. grandis, C. paradisi, and in some cultivars of C. reticulata, but was absent in most citrus species and cultivars (e.g., C. aurantifolia (Christm.) Swing., C. canaliculata Hort. ex Y. Tan., C. hystrix, C. limon, C. medica, C. sinensis). It was found that some species which failed to exhibit the adventitious branching phenomenon in nature did so in vitro (e.g., C. hystrix, C. medica, and C. sinensis).
RESTRICTION FRAGMENT ANALYSIS OF CHLOROPLAST DNA AND THE SYSTEMATICS OF VIGUIERA AND RELATED GENERA (ASTERACEAE: HELIANTHEAE)
Authors: Schilling Edward E. , Jansen Robert K.
Published: January 2018

Phylogenetic relationships among 31 species representing variously Helianthus, Helianthopsis, Heliomeris, Simsia, Viguiera, and Tithonia were assessed by chloroplast DNA restriction site mapping. A total of 147 mutations including 92 informative ones was detected using 16 restriction enzymes, with an estimated sequence divergence within the group of 1.4%. Parsimony analysis produced a single most parsimonious tree with a length of 161 steps and a consistency index of 0.91. Statistically significant clades, as assessed by the bootstrap method, correspond to a number of taxa recognized previously, including Helianthus (3 species), Helianthopsis (5 species), and several groups within Viguiera, including sect. Maculatae (4 species), the Baja California group (6 species), sect. Paradosa (2 species) and V. dentata (3 samples). However, species of Viguiera collectively form a highly paraphyletic group relative to species of other genera. Helianthus and Helianthopsis were separated into different clades, supporting their recent segregation. Placement of H. porteri in Helianthus rather than Heliomeris was confirmed; the single sample of the latter genus was most similar to the Baja California group of Viguiera. An expected relationship between Simsia (2 species) and one member of Viguiera ser. Grammatoglossae was confirmed (although not with two other putatively related members of Viguiera) and an unexpected relationship between Simsia and Tithonia was suggested. The presence of Mexican taxa as the more basal groups in the tree points toward a possible Mexican origin for Viguiera and related genera. A molecular clock hypothesis is rejected in many pairwise comparisons involving woody taxa with herbaceous ones, although it could not be rejected in most pairwise comparisons involving taxa of similar habit.
MOLECULAR DIVERGENCE BETWEEN ASIAN AND NORTH AMERICAN SPECIES OF LIRIODENDRON (MAGNOLIACEAE) WITH IMPLICATIONS FOR INTERPRETATION OF FOSSIL FLORAS
Authors: Parks Clifford R. , Wendel Jonathan F.
Published: January 2018

Botanists have long been aware of the floristic similarities between eastern Asia and eastern North America. Most who have considered this classic disjunction pattern have suggested that it arose through range disruption of a flora that was once more widely distributed in the Northern Hemisphere. There is less agreement on the timing of this process, with suggestions ranging from the Paleocene to the Neogene. In this study, molecular markers from two different plant genomes were used to assess the degree of genetic divergence between the two interfertile, morphologically similar species of the genus Liriodendron, i.e., L. tulipifera and L. chinense. Resulting molecular divergence estimates were translated into approximate dates of separation, independent of evidence from the fossil record. Allozyme data (Nei's genetic identity = 0.434) suggested a divergence time of 10–16 million years before present, whereas sequence divergence in the plastid genomes (1.24%) led to an estimate of approximately 11–14 million years before present. A review of the paleobotanical literature indicated that the fossil floras that included, or might have included Liriodendron could not have survived in Beringia after the late Miocene and the onset of southward‐migrating Arctic air masses on the North American continent. This interpretation suggests a minimum time of separation of approximately 13 million years before present. Thus, both molecular data sets and the paleobotanical evidence concur in suggesting a divergence time of 10–16 million years before present. Interspecific compatibility and relative morphological stasis must have, therefore, persisted from at least the late Miocene. We emphasize the need for similar studies in other genera, especially those that have both a reasonable Tertiary fossil history and extant species in mesic temperate refugia in Asia, Europe, and western as well as eastern North America.