Molecular evidence on the species status and phylogenetic relationships of Spiranthes parksii, an endangered orchid from Texas

Abstract

New genetic information on the taxonomic status of an endangered species may have strong implications for its continued protection and that of other listed taxa with questionable species status. While analyzing a more comprehensive project on the molecular phylogeny of North American Spiranthes (Orchidaceae), lack of genetic differentiation between endangered S. parksii, endemic only to Texas, and a common local congener, S. cernua, was discovered. To confirm these results in a comparative context, we focused parsimony analyses on a subset of data from local Spiranthes and the same congeners found elsewhere, expanded by additional local samples of the two focal species. Four DNA sequence segments (two chloroplast, one mitochondrial, one nuclear ribosomal) totaling 3191 base pairs were used separately and together to verify that S. parksii is nested within the same clade as S. cernua, and thus likely to be the same species. Our results concur with another recent investigation using AFLP and microsatellite data that also suggests S. parksii is not unique genetically. Therefore, based on empirical data and the phylogenetic species concept, endangered S. parksii is merely an aberrant local phenotype of and a synonym for S. cernua sensu lato. Our results should be considered during the current review of this orchid's listing status, despite some recent policy changes on consideration of genetic data after listing.

A sequential approach using genetic and morphological analyses to test species status: The case of United States federally endangered Agalinis acuta (Orobanchaceae)

“…Similar to our conclusions, an investigation of the evolutionary distinctiveness of the federally listed narrowly endemic species Spiranthes parksii (Orchidaceae) from the more widespread Spiranthes cernua suggested the two be synonymized (Dueck and Cameron, 2008). The two species are often sympatric, possess many morphological similarities, and the differences that have been used historically to differentiate S. parksii were considered to reflect locally distinct phenotypes of the more widespread and variable S. cernua (Dueck and Cameron, 2008). Phylogenetic analyses of 3191 bp representing four DNA sequence loci showed S. parksii to be nested within S. cernua .…”

“…Consequently, the authors recommended that the two species be synonymized but also stated that the impact of their results on the conservation of S. parksii ultimately rests with the USFWS. Although we have also suggested that synonymization is warranted, the conservation implications differ between our study and Dueck and Cameron (2008) given that A. decemloba populations also appear to be of conservation concern (see discussion below).…”

A molecular framework for understanding the phylogeny of Spiranthes (Orchidaceae), a cosmopolitan genus with a North American center of diversity

“…Another example of the taxonomic uncertainties that complicate the conservation of Spiranthes is the disputed species status of federally endangered S. parksii Correll, which, as a peloric mutant, is likely to be only an aberrant local phenotype of widespread S. cernua (L.) Rich. (Dueck and Cameron, 2008). These are but a few cases in Spiranthes where having accurate taxonomic information for vulnerable species listed on ecological inventory checklists can have profound implications for habitat protection and conservation.…”

The Pollination Biology of North American Orchids: Volume 2

“…This would provide sufficient genetic diversity to account for the amount of allozyme variation observed in this population (Schmidt and Antlfinger 1992). S. parksii Correll, described as a facultatively agamospermous tetraploid species endemic to postoak savannas in East Central Texas (Catling and McIntosh 1979;Sheviak and Brown 2002), is not distinct from S. cernua Dueck and Cameron 2008). Schmidt (1987) suggested that the high proportion of agamospermic seeds produced in eastern Nebraska populations of S. cernua might be due to pollinator limitation (discussed below under sexual populations) or to the precocious development of adventitious embryos prior to anthesis.…”

“…Ten other Spiranthes taxa occur in North America north of Florida and Mexico: S. porrifolia Lindley (creamy ladies'-tresses), S. stellata P. M. Brown, Dueck, and Cameron (no common name), S. infernalis Sheviak (ash meadows ladies'-tresses), S. delitescens Sheviak (reclusive ladies'-tresses), S. longilabris Lindley (giant spiral ladies'-tresses), S. brevilabris Lindley (texas ladies'-tresses), S. floridana (Wherry) Cory (florida ladies'-tresses), S. eatonii Ames ex P. M. Brown (eaton's ladies'-tresses), S. praecox (Walter) S. Watson (greenvein ladies'-tresses), and S. sylvatica P. M. Brown (woodland ladies'-tresses), although the latter may not be distinct from S. praecox (Dueck and Cameron 2008). Nothing is yet known of their pollination biology.…”