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It has long been suggested that phylogenetic divergence between parental species determines the likelihood of their producing a successful polyploid, with closely related parents less likely to form a successful polyploid than more divergent parents. This suggestion has been based partly on observation of patterns of polyploid ancestry and partly by extrapolation from analyses of the processes that give rise to polyploids. Here we present a new survey of the patterns of the divergence between the parents of polyploids, based on node-based and clade-based analyses of phylogenetic trees. We also use the topology of the phylogenetic trees to inform a null expectation of the distance between parental species, assuming random crossing between all species pairs in a genus. We used molecular phylogenies now available for eight plant genera containing multiple polyploids whose parentage has been investigated: Tragopogon, Persicaria, Brassica, Leucaena, Spartina, Spiranthes, Nicotiana, and Glycine. We found that the phylogenetic distance between progenitors of polyploids did not differ significantly from the null expectation. In contrast, the distance between parents of diploid hybrids (both stable and unstable) in these genera were lower than would be expected with random crossing. We discuss how these findings may fit with recent progress, through genetic and genomic studies, in understanding the processes involved in polyploidization.
Leitneria floridana is a rare woody species with a disjunct distribution in the southeastern and south-central United States. Although the distribution of L. floridana is well established, little is known about the comparative biology of its disjunct populations or the factors contributing to its rarity. We studied populations of L. floridana in Missouri, Arkansas, Texas, and Florida to characterize and compare population density, habitat, ecophysiology, morphology, and growth. Our results show that plants of the Missouri provenance are the most unique phenotypically, plants in Texas are the fastest growing, and plants in Arkansas seem particularly adapted to shade. We found that L. floridana grows in chemically and physically diverse soils and under a broad range of insolation. Soil moisture content appears to be the most important environmental factor governing the occurrence of L. floridana, with soil moisture and distribution density positively correlated.
Lynch's Woods Park (Newberry County, South Carolina) was floristically surveyed between 2002 and 2005. The Park features north-facing slopes, granite outcrops, and several small streams within the Piedmont physiographic province. A total of 528 vascular plant species were documented within the 101.2 ha, including 91 (17%) nonnatives. Three species, Anemone berlandieri, Eurybia mirabilis, and Rhododendron eastmanii were rare species. Analysis of community structure revealed that most of the area was a mixed mesophytic forest, with the upland sites developing toward an oak-hickory forest.
A total of 519 plant taxa have been added to the known flora of Great Falls Park, Fairfax County, Virginia, since the vascular flora was first published more than 30 yr ago. Species erroneously reported from the Park are noted. To date, 1,015 vascular plant taxa representing 1,002 species, eight infraspecific taxa, and five hybrids from 492 genera in 139 families have been documented within the Park. Of these, 76 are known only from historical specimens. Twenty-three of the documented plants are listed as rare in the Commonwealth of Virginia. Non-native taxa comprised 19.8% of the vascular flora in the Park. Ecological community types of the Park are described and listed for each associated taxon.
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