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Summary Tropical mountains are disproportionately biodiverse relative to their surface area, but the processes underlying their exceptional diversity require further study. Here, we use comparative phylogenetic methods to examine the... more
Summary Tropical mountains are disproportionately biodiverse relative to their surface area, but the processes underlying their exceptional diversity require further study. Here, we use comparative phylogenetic methods to examine the impact of the Andean orogeny on the diversification of Neotropical Phlegmariurus, a species‐rich lycophyte clade. We generated a time‐calibrated phylogeny of 105 species of Neotropical Phlegmariurus and estimated lineage diversification rates. We tested for correlations between lineage diversification rates and species range size, niche breadth, elevational range amplitude, and mean elevation of occurrence. A recently developed macroevolutionary model was used to incorporate geological data and test for an association between diversification rates and the Andean uplift. Diversification rates of Neotropical Phlegmariurus are negatively correlated with species range size and positively correlated with mean elevation of species occurrence. The rise of the ...
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The Neotropical clade of the lycophyte genus Phlegmariurus is comprised of an estimated 150 described species and exhibits exceptional morphological and ecological diversity. Because of their simple morphology, frequent convergent... more
The Neotropical clade of the lycophyte genus Phlegmariurus is comprised of an estimated 150 described species and exhibits exceptional morphological and ecological diversity. Because of their simple morphology, frequent convergent evolution, and the recentness of the group's diversification, the delimitation of species and species groups has remained challenging. Here, we present a robustly support phylogeny of Neotropical Phlegmariurus based on six chloroplast markers and ca. 70% of known species, and use ancestral character state reconstruction to investigate morphological evolution in the clade, and define natural species groups. The Neotropical species of Phlegmariurus form a clade that also includes a small number of Afro-Madagascan species. A morphologically and ecologically variable group of species from southeastern Brazil form a monophyletic group and represent a parallel radiation to principally Andean lineages. Species groups in Neotropical Phlegmariurus that were pre...
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The large retromer complex participates in diverse endosomal trafficking pathways and is essential for plant developmental programs including cell polarity, programmed cell death, and shoot gravitropism in Arabidopsis. Here we demonstrate... more
The large retromer complex participates in diverse endosomal trafficking pathways and is essential for plant developmental programs including cell polarity, programmed cell death, and shoot gravitropism in Arabidopsis. Here we demonstrate that an evolutionarily conserved VPS26 protein (VPS26C; At1G48550) functions in a complex with VPS35A and VPS29 necessary for root hair growth in Arabidopsis. Bimolecular Fluorescence Complementation showed that VPS26C forms a complex with VPS35A in the presence of VPS29 and this is supported by genetic studies showing that vps29 and vps35a mutants exhibit altered root hair growth. Genetic analysis also demonstrated an interaction between a VPS26C trafficking pathway and one involving the SNARE VTI13. Phylogenetic analysis indicates that VPS26C, with the notable exception of grasses, has been maintained in the genomes of most major plant clades since its evolution at the base of eukaryotes. To test the model that VPS26C orthologs in animal and plan...
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SUMMARYNon-random collecting practices may bias conclusions drawn from analyses of herbarium records. Recent efforts to fully digitize and mobilize regional floras offer a timely opportunity to assess commonalities and differences in... more
SUMMARYNon-random collecting practices may bias conclusions drawn from analyses of herbarium records. Recent efforts to fully digitize and mobilize regional floras offer a timely opportunity to assess commonalities and differences in herbarium sampling biases.We determined spatial, temporal, trait, phylogenetic, and collector biases in ∼5 million herbarium records, representing three of the most complete digitized floras of the world: Australia (AU), South Africa (SA), and New England (NE).We identified numerous shared and unique biases among these regions. Shared biases included specimens i) collected close to roads and herbaria; ii) collected more frequently during spring; iii) of threatened species collected less frequently; and iv) of close relatives collected in similar numbers. Regional differences included i) over-representation of graminoids in SA and AU and of annuals in AU; and ii) peak collection during the 1910s in NE, 1980s in SA, and 1990s in AU. Finally, in all region...
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Polystichum is one of the most diverse genera of ferns, with 360–400 species distributed worldwide. South America harbors ~40 species, clustered in three centres of diversity, namely, the Northern and Central Andes Center (NCC), the... more
Polystichum is one of the most diverse genera of ferns, with 360–400 species distributed worldwide. South America harbors ~40 species, clustered in three centres of diversity, namely, the Northern and Central Andes Center (NCC), the Brazilian Center (BC) and the Southern South America Center (SSC). To increase our understanding of the systematic relationships within Polystichum, mitotic chromosomes and spore features were studied in nine species from Argentina and Chile. All species presented the basic number x = 41, with different ploidy levels (2x, 4x and 8x). In general, chromosomes were homogeneous in size (average length 2.50–5.75 µm) and mostly subtelocentric; centromeres were inconspicuous and secondary constrictions were frequently observed. All species presented 64 spores per sporangium, suggesting normal sexual reproduction. Significant differences in spore size were found among species and it was positively correlated with ploidy level. A relationship between sum total ch...
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Hybridization is an important evolutionary force in plants, but the mechanisms underlying it have not been well studied for many groups. In particular, the drivers of non-random patterns of interspecific gene flow (asymmetrical... more
Hybridization is an important evolutionary force in plants, but the mechanisms underlying it have not been well studied for many groups. In particular, the drivers of non-random patterns of interspecific gene flow (asymmetrical hybridization) remain poorly understood, especially in the seed-free vascular plants. Here, we examine patterns of asymmetrical hybridization in two widespread fern hybrids from eastern North America and study the role of gametophyte ecology in the determination of hybridization bias. We characterized the maternal parentage of > 140 hybrid sporophytes by sequencing a c. 350-bp region of chloroplast DNA (cpDNA). To identify factors contributing to patterns of asymmetrical hybridization, we cultured gametophytes of the parental species and evaluated critical aspects of their reproductive biology. We found that asymmetrical hybridization was prevalent across the populations of both hybrids. Reproductive traits varied across species and suggest that selfing po...
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Studies of soral development in the tree-fern family Dicksoniaceae in comparison with the Cyatheaceae led to (1) recognition of two basic patterns in the Dicksoniaceae, (2) clarification of marginal versus superficial sori and their... more
Studies of soral development in the tree-fern family Dicksoniaceae in comparison with the Cyatheaceae led to (1) recognition of two basic patterns in the Dicksoniaceae, (2) clarification of marginal versus superficial sori and their indusia in tree ferns, and (3) phylogenetic interpretations. In Cibotium the sorus originates directly from the marginal initial file. The outer and inner indusia arise simultaneously, early in development, on the adaxial and abaxial sides of the receptacle, respectively. The receptacle in Dicksonia originates from a shifted segment of the marginal initial file. The outer indusium is initiated first, approximately at the same time as the receptacle. The initial cells of the marginal meristem give rise to the soral receptacle in both groups of dicksoniaceous genera. Preliminary studies of soral morphogenesis in some cyatheaceous genera indicate that abaxial derivatives originate the sorus. The Cyatheaceae have a single, abaxial indusium proximal to the so...
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Research Interests: Plant Biology and fERN
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— The generic classification of the Thelypteridaceae has been the subject of much controversy. Proposed taxonomic systems have varied from recognizing the approximately 1200 species in the family within the single genus Thelypteris, to... more
— The generic classification of the Thelypteridaceae has been the subject of much controversy. Proposed taxonomic systems have varied from recognizing the approximately 1200 species in the family within the single genus Thelypteris, to systems favoring upwards of 30 genera. Insights on intrafamilial relationships, especially for neotropical taxa, have been gained from recent phylogenetic studies; however, in the most recent classification, 10 of 30 recognized genera are either non-monophyletic or untested. We sequenced 407 nuclear loci for 621 samples, representing all recognized genera and approximately half the known species diversity. These were analyzed using both maximum likelihood analysis of a concatenated matrix and multi-species coalescent methods. Our phylogenomic results, informed by recently published morphological evidence, provide the foundation for a generic classification which recircumscribed 14 genera and recognized seven new genera. The 37 monophyletic genera sampled demonstrate greater geographic coherence than previous taxonomic concepts suggested. Additionally, our results demonstrate that certain morphological characters, such as frond division, are evolutionarily labile and are thus inadequate for defining genera.
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The fern genus Polystichum has presented major problems in definition and circumscription of species since its description by Roth in 1799. Part of the problem is the vast diversity within the genus: the number of species is reported as... more
The fern genus Polystichum has presented major problems in definition and circumscription of species since its description by Roth in 1799. Part of the problem is the vast diversity within the genus: the number of species is reported as more than 175 by Copeland (1947). In addition, hybridization is extremely common (Knobloch, 1976), and agamospory has been reported among experimental plants from Europe (Vida & Reichstein, 1975). There is also substantial evidence of phenotypic and ontogenetic variability within species of the genus. Good progress has been made in solving evolutionary and taxonomic problems in the north-temperate and boreal regions (Manton, 1950; Manton & Reichstein, 1961; Kurata, 1964; Sleep & Reichstein, 1967; Daigobo, 1972; W. Wagner, 1973; D. Wagner, 1979); however, little taxonomic and virtually no evolutionary work has been done on the genus in tropical or austral regions. Hence this large genus of dryopteroid ferns is in need of substantial attention from systematic and evolutionary biologists, especially in tropical regions. Christopher Haufler at the University of Kansas organized a symposium on Polystichum for the American Institute of Biological Sciences meetings in Fort Collins, Colorado, during August of 1984. As Haufler noted in his opening remarks, the purpose of the symposium was to draw attention to a complex and poorly understood genus of ferns, rather than to solve problems by consensus of the speakers. Participants in the symposium focused on the evolutionary problems encountered in New World Polystichum, primarily from a taxonomic and floristic viewpoint. This paper summarizes the Fort Collins symposium.