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The two recent theories of flowering plant evolutionary origins—the Anthophyte and Neo-Pseudanthial theories—are based on phylogenies (from morphological data) that show Gnetales as extant sister to angiosperms or as paraphyletic to angiosperms. Gnetales figured prominently in homology assessments and evolutionary scenarios of these theories. Several recent studies, including ours, provide strong evidence that extant gymnosperms are monophyletic, so Gnetales are most closely related to other gymnosperms, not to flowering plants. This removes the basis for both recent theories, leaving earlier theories that relate flowering plants to fossil “seed-fern” gymnosperms as the only active contenders. Our data from the homeotic gene Floricaula/LEAFY imply that the lineage leading to flowering plants originally had two copies of this gene, but that one copy was lost in flowering plants, which suggests a new theory: that developmental control of flower organization derives more from systems active in the male reproductive structures of the gymnosperm ancestor, rather than from the female, with ovules being ectopic in the original flower. This theory was based entirely on data from living plants, but the fossil group Corystospermales has both male and female structures that fit the theory. Corystosperms could include ancestors of the flowering plants.
Unlike most highly outcrossing flowering plants, milkweeds (Asclepiadaceae) have exceptionally low pollen-ovule ratios. We counted the number of pollen grains contained within a pollinium sac and the number of ovules contained within an ovary for 38 species of Asclepiadaceae. Across four tribes of the Asclepiadoideae, the number of pollen grains per pollinium varied from 14 to 445, and the number of ovules per ovary varied from 4 to 229. Nevertheless, the pollen-ovule ratio was constrained within a narrow range, generally 1 to 2. Similar constraints on pollen-ovule ratios occur within mimosoid legumes (Acacia, Calliandra, Inga) whose pollen also is dispersed in clusters (polyads). Our data are consistent with the view that agglutination of pollen evolves in concert with ovule number to minimize the likelihood of receiving mixed pollen loads and are not consistent with the view that pollen-ovule ratios reflect breeding system or pollination efficiency. Trends in pollen grain and ovule number do not appear to reflect taxonomic affinities, but rather ecogeographical pressures.
Phylogenetic placement of Puelia and Guaduella, two broad-leaved African grass genera traditionally classified as bamboos, is inferred from analysis of ndhF, rbcL, and PHYB sequence data. Puelia and Guaduella are supported as sister genera, and the Puelia/Guaduella clade is resolved as an early diverging branch within the Poaceae and sister to the BEP PACC clades, which include the bulk of the family. The new grass subfamily Puelioideae is described to accommodate the Puelia/Guaduella clade.
A new moss species, Schizymenium shevockii, is described from Fresno County, California. Schizymenium shevockii is distinguished from North American species of Mielichhoferia by a single endostomial peristome, and from Mexican species of Schizymenium by dioicous sexuality, poorly developed endostome segments, and the complete absence of exostome teeth. The new species can also be distinguished from S. pontevedrensis (the only European species of that genus), Mielichhoferia mielichhoferiana, and Mielichhoferia elongata by the presence of 38 and 29 nucleotide (nt) deletions in the ITS1 region of nuclear ribosomal DNA, and a nine nt insertion in the ITS2 region. Four additional insertions and/or deletions distinguish S. shevockii from M. elongata and/or M. mielichhoferiana. Moreover, Mielichhoferia elongata and M. mielichhoferiana share 34 nucleotide substitutions that distinguish them (as a monophyletic group) from S. shevockii and S. pontevedrensis. A survey of California populations using primers designed to take advantage of molecular differences between S. shevockii and morphologically similar but sterile plants of Mielichhoferia elongata revealed plants of S. shevockii at three sites. At one such site, S. shevockii was sympatric with M. elongata. All samples of S. shevockii had identical ITS sequences.
The Halesia carolina complex has consisted of several poorly defined taxa endemic to the southeastern United States. To help resolve the taxonomy of this complex, seventeen morphological characters thought to be of taxonomic utility were measured from 286 herbarium specimens collected throughout the range of the complex and analyzed with Pearson's correlations. No character exhibits a distinct gap in character states; rather, most characters display broadly clinal patterns of variation that are significantly associated with latitude. Several characters also exhibit significant partial correlations. Principal components analysis does not reveal distinct clusters. The apparently concordant clines spanning the range of the complex suggest secondary contact of at least two formerly isolated groups, possibly a result of Quaternary glacial cycles. Morphological intergradation among populations is now so extensive as to preclude the recognition of more than a single species, H. carolina, without infraspecific divisions. The taxonomy of the complex is revised accordingly herein. An updated distribution map based on nearly 400 collections, full synonymy, and a description of H. carolina are included.
Phylogenetic relationships in the myrmecophytic genus Tococa (Melastomataceae) were investigated using morphological data. The data matrix comprised 42 ingroup taxa, two of them previously described as Microphysca, the monotypic genus Myrmidone, and 11 species of the genus Miconia as outgroups. Vegetative and floral characters were used, in addition to characters drawn from seeds using both light and electron microscopy. A cladistic analysis of the morphological matrix, containing 58 informative characters, resulted in 224 most parsimonious trees. This analysis shows that Tococa is not monophyletic, both because there are some species of Tococa more closely related to Miconia than to the remaining species of Tococa, and because Myrmidone and Microphysca are nested within Tococa. However, it is possible to recognize a large, well-supported clade that includes Myrmidone and most species of Tococa. This clade is here defined as Tococa sensu stricto. The tooth in the dorsal side of the anther connective that has been informally proposed in the past as a synapomorphy for Tococa, although present in most species of Tococa sensu stricto, is not a synapomorphy for the genus. Synapomorphies for Tococa sensu stricto include the presence of emarginate petals, truncate ovaries and straight anticlinal walls in the cells of the seed testa. Within Tococa sensu stricto, ant domatia have evolved at least twice, and have been secondarily lost at least once.
Isozymes were examined in the six aquatic (including amphibious) diploid species of Isoetes of eastern North America in order to quantify their levels and patterns of genetic variation, to determine their genetic distinctness, and to evaluate the utility of allozymes in addressing ancestry in the I. riparia complex. Twenty-six populations representing diploid species, I. echinospora, I. engelmannii, I. flaccida, I. mattaponi, I. prototypus, and I. valida were compared for eleven enzymes coded by 16 interpretable loci. Levels of genetic variation in populations tended to be low ranging from none (means: P = 0.0, A = 1.0, H = 0.0) in I. echinospora to moderate (means: P = 22.9, A = 1.4, H = 0.093) in I. flaccida. Genetic variation in polymorphic species tended to be distributed more among than within populations, as indicated by high Fst values (Fst > 0.607 in all polymorphic species except I.mattaponi, for which Fst = 0.272). The genetic identities of conspecific populations were high, with mean values ranging from I = 0.779/S = 0.733 in I. flaccida to I = 1.000/S = 1.000 in I. echinospora. Interspecific genetic identities were lower, with means ranging from I = 0.438/S = 0.429 between I. mattaponi and I. prototypus to I = 0.736 between I. valida and I. flaccida, and S = 0.699 between I. valida and I. prototypus. Thus the six diploids were found to be genetically distinct, corroborating their recognition based on morphology. Evidence from this study indicates that isozymes may be informative in diagnosing ancestry of allopolyploids in the Isoetes riparia complex.
Isoetes riparia is a complex tetraploid taxon of eastern North America that in its widest sense includes a diversity of morphotypes variously segregated, or included in a single polymorphic species. Although the diploid ancestry of I. riparia has been proposed as I. echinospora × engelmannii, it is uncertain whether this ancestry applies to all elements of the complex, here broadly defined to encompass three segregates of I. riparia and the recently described I. hyemalis (referred to informally as riparia, canadensis, saccharata and hyemalis). To help clarify relationships among these tetraploids, isozyme genotypes for 13 loci coding eight enzymes, were determined for 16 populations representing all four segregates. Duplicate gene expression, evidenced as fixed heterozygosity consistent with allopolyploidy, characterized the tetraploid genotypes of all taxa. Although exhibiting modest to no variation within populations, populations were highly differentiated, most showing a unique combination of alleles for their multilocus genotypes, with the exception of five genetically identical Canadian populations. Ancestry was evaluated through comparison to diploid genotypes previously reported. A quantitative approach was carried out to rank likelihoods for hypothetical ancestral combinations of diploids for each tetraploid population. The ancestry I. echinospora × engelmannii hypothesized for I. riparia was unequivocally supported for the six populations of the most northern segregate, canadensis. Diploid ancestries for the remaining 10 more southern populations were less certain, although the diploid I. mattaponi was implicated as a likely ancestor for most. Most likely ancestry for populations of riparia/saccharata was inferred as I. valida × mattaponi, and for hyemalis as I. mattaponi × flaccida. However, these hypotheses were only slightly more likely than other combinations. UPGMA analysis using Rogers' similarity resulted in three clusters corresponding to canadensis, riparia/saccharata, and hyemalis. However, the hyemalis cluster was weakly associated and was not supported by UPGMA using Nei's identity. These highly variable tetraploid genotypes suggest a complicated evolutionary history for the I. riparia complex that probably involved a combination of diverse ancestry, multiple origins, divergence, and gene silencing.
Allozyme and morphological analyses were conducted to test speculation and recently published taxonomy concerning northern versus southern variation in the Cypripedium parviflorum complex. Allozyme analyses of 40 populations from 10 states revealed marked differences in genetic variation between northern and southern populations of var. pubescens, and between var. makasin and var. parviflorum. For both comparisons, the northern populations from previously glaciated regions generally contain more genetic variation and larger estimated population sizes than do their southern counterparts. These results are in contrast to most published findings on other taxa that report higher levels of genetic variation in populations near glacial refugia compared to conspecifics from previously glaciated territory. To explain the data in our paper, we suggest the existence of a northern refugium for C. parviflorum in a periglacial environment that contained abundant habitat for this species. This region could have served as a genetically diverse source of propagules for colonizing newly deglaciated territory. Conversely, populations in the heavily forested south may have remained relatively small and isolated throughout glaciation, promoting genetic drift and the loss of genetic variation. Lastly, var. makasin differs from the other two varieties in mottling and coloration of the dorsal sepal, and in pubescence on the uppermost, nonphotosynthetic sheathing leaf. These data are consistent with previous hypotheses of northern versus southern differentiation in C. parviflorum, and support recognition of newly restored var. makasin.
The remarkable morphological diversity of the palm subfamily Calamoideae provides a paradigm for evolutionary studies of palm structure and function. Phylogenetic relationships among the 22 calamoid genera are investigated here in simultaneous analyses of morphological data and DNA sequences from nuclear ITS regions and the chloroplast rps16 intron. The resultant hypotheses of relationship are used to explore morphological character evolution through an examination of character state optimisations. The evolution of habit and its associated characters is found to be highly homoplasious; for example, multiple origins of both the acaulescent and climbing growth forms have been identified. Similarly, life history and reproductive characters show complex patterns of evolution with few primary homology assessments proving to be effective judgements of synapomorphy. Many of these homoplasious characters were emphasized in the previous classification of the Calamoideae and consequently some non-monophyletic groups were recognized formally. We present a new classification in which a number of unexpected, group-defining characters, such as the number of pollen apertures, have been identified. The classification comprises three tribes and nine subtribes, including one newly described tribe Eugeissoneae. However, the morphology of many well supported clades remains poorly understood, creating further challenges for future studies in calamoid phylogeny.
The goals of this study were to elucidate phylogenetic relationships in Eleocharis (Cyperaceae) using the nuclear ribosomal internal transcribed spacer (ITS) region, and compare this phylogeny with three infrageneric classifications. Thirty Eleocharis species and eight outgroups were analyzed using maximum parsimony and maximum likelihood analyses. These analyses place Websteria within the Eleocharis clade. The sister group of Eleocharis has traditionally been inferred to be either members of the Abildgaardieae or Scirpeae. Theses analyses do not show strong support for Bulbostylis (Abildgaardieae) or Schoenoplectus (Scirpeae) as the sister lineage to Eleocharis. The ITS results are not entirely congruent with any of the classifications. There is support for a monophyletic Eleocharis subgenus Limnochloa and subgenus Zinserlingia sensu González-Elizondo and Peterson, but many of the subdivisions of Eleocharis subgenus Eleocharis are para- or polyphyletic. Morphological characters inferred to have multiple origins by the ITS data, and qualitative traits such as texture, shape and color of nuts and scales, and shape and texture of sheath apices have been used to define classification units in Eleocharis and this appears to have played a major role in the confusion surrounding relationships in the genus.
Phylogenetic relationships among 43 accessions of Fragaria, representing 14 species, and one accession of the outgroup Potentilla fruticosa, were assessed using nucleotide sequence data from the nuclear ITS region and from a region of the chloroplast genome including the trnL intron and the trnL-trnF spacer. Variability was low in both regions and lower in the chloroplast than in the nuclear sequences. The data were analyzed cladistically, separately and in combination. Greater phylogenetic resolution was obtained with the ITS and combined data than with the trn data; the strict consensus tree from the combined data analysis was very similar to that from the ITS analysis, but the position of some accessions was affected by the inclusion of the trn data. The results support the following conclusions: Fragaria iinumae is sister to all other species in the genus; F. vesca and F. nubicola are the diploid species most closely related to the polyploid species, including the tetraploid F. orientalis, the hexaploid F. moschata, and the octoploids F. chiloensis and F. virginiana; the latter two species are sister taxa; accessions of F. virginiana subsp. platypetala from Oregon and Nevada are more closely related to F. chiloensis than to other accessions of F. virginiana. The data provide support for the identification of some accessions in the National Clonal Germplasm Repository in Corvallis, Oregon.
Phoradendron is a genus of morphologically diverse mistletoes that currently lacks a satisfactory supraspecific classification. Its subtle distinction from Dendrophthora moreover suggests that Phoradendron may not be monophyletic. This study uses sequences from three regions of the nuclear ribosomal DNA cistron to infer phylogenetic relationships in the two genera. These DNA regions differ in their rates of nucleotide substitution. Sequences of the ITS spacers are sufficiently variable to resolve relationships among closely related species but are barely alignable with those of more distantly related species and outgroups. Alignment is possible, however, among sequences of the 5.8S gene and among two regions of the 26S nuclear rDNA. Maximum parsimony analyses suggested that neither Phoradendron nor Dendrophthora is monophyletic. Three major clades were identified whose topologies suggest that many characters traditionally used for primary subdivision are homoplastic.
Parsimony analysis of nucleotide sequences of the plastid gene rbcL and non-coding trnL-F region was used to examine phylogenetic relationships of 36 members of Zygophyllaceae, especially of the four genera forming subfamily Zygophylloideae (Zygophyllum, Fagonia, Tetraena and Augea). The two data sets were analyzed separately, and in combination. Results of the three analyses were largely in agreement and support previous division of Zygophyllaceae into five subfamilies. Zygophylloideae were further divided into five clades each with high bootstrap support, although the branches connecting these clades are poorly supported. Zygophyllum appears polyphyletic and may need further revision. The taxonomic positions of Morkillia, Sericodes, Pintoa, and Tribulopis are also clarified.
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