Species delimitation and recognition in the Pediomelummegalanthum complex (Fabaceae) via multivariate morphometrics.

Ashley N Egan

doi:10.3897/phytokeys.44.8750

Abstract

Pediomelum is a genus endemic to North America comprising about 26 species, including the megalanthum complex, which consists of Pediomelum megalanthum and its varieties retrorsum and megalanthum, Pediomelum mephiticum, and the recently described Pediomelum verdiense and Pediomelum pauperitense. Historically, species of the megalanthum complex have been variably recognized at the species or variety levels, dependent upon the relative importance of morphological characters as diagnostic of species. Ten quantitative morphological characters regarded as diagnostic at the species level were analyzed using multivariate morphometrics across these taxa in order to examine the discriminatory power of these characters to delineate species and to aid in species delimitation. The analyses support the recognition of Pediomelum megalanthum, Pediomelum mephiticum, and Pediomelum verdiense at the species level, Pediomelum retrorsum as a variety under Pediomelum megalanthum, and suggest the sinking of Pediomelum pauperitense into Pediomelum verdiense. The findings of the present study help quantify the power of certain characters at delimiting taxa and provide a basis for taxonomic revision of the Pediomelum megalanthum complex.

Highlights

Pediomelum Rydb. (Psoraleeae; Leguminosae) includes about 26 species, all native to North America (Rydberg 1919)
Taxonomic identifications were initially accepted according to the most recent annotation on the specimens. Those recognized at the specific vs. subspecies levels with the same epithet were analyzed together, i.e. P. retrorsum was grouped in analyses with P. megalanthum var. retrorsum
Three character pairs across all species had correlation coefficients above 0.8 in either the positive or negative direction: P. verdiense had a correlation coefficient of 0.8775 for calyx:lower calyx tooth; P. m. var. retrorsum exhibited a negative correlation of -0.8108 for pedicel:bract; P. pauperitense exhibited a correlation of 0.8783 for flower:bract

Summary

Introduction

Pediomelum Rydb. (Psoraleeae; Leguminosae) includes about 26 species, all native to North America (Rydberg 1919). The genus radiated recently and rapidly, with diversification shifts taking place within the last 2 mya, likely due to the impacts of Pleistocene glaciations (Egan and Crandall 2008a) This recent radiation is illustrated in the shallow branch lengths within phylogenies, relative to related genera within the Psoraleeae tribe, even phylogenies based on a combined dataset of eight DNA markers (Egan and Crandall 2008b). This is reflected in the disparate taxonomic views among botanists, with several taxa variably recognized at specific or varietal levels. On the other hand, Welsh et al (1993) utilized directionality of pedicel and peduncle hairs (P. retrorsum Rydb. vs. P. megalanthum) and absence of pubescence on the upper leaf surface (P. epipsilum (Barneby) S.L.Welsh) as diagnostic characters to maintain their distinctiveness

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Conclusion