Patterns of Morphological and Plastid DNA Variation in the Corallorhiza striata Species Complex (Orchidaceae)

Abstract

Corallorhiza striata is a wide-ranging, morphologically variable, mycoheterotrophic species complex distributed across North America. Objectives of this study were to assess relationships and test validity of previously delimited varieties of C. striata, including the recently described C. bentleyi. Two plastid DNA regions were sequenced for individuals from several populations across North America, identifying four major clades. The large-flowered C. striata var. striata (northern U.S.A., southern Canada) was sister to the smaller-flowered var. vreelandii (southwestern U.S.A., Mexico), and these were sister to a Californian clade with relatively intermediate-sized flowers. C. striata var. involuta (Mexico) and the endangered C. bentleyi (eastern U.S.A.) shared a close relationship, sister to the remaining C. striata. Principal Components Analysis and Nonparametric Multivariate Analysis of Variance on nine quantitative morphological characters, using plastid DNA clades as independent variables, demonstrated strong correlations between molecular and morphological groupings. Morphological analyses supported differentiation of both C. striata var. involuta and C. bentleyi relative to all other accessions of C. striata, suggesting their recognition as separate species; these findings will have future implications for conservation. The biogeographic scenario was more complex than previously thought, with members of two major plastid DNA lineages (C. bentleyi/var. involuta and the remaining C. striata) existing in Mexico and U.S.A./Canada. These findings contribute to a burgeoning body of data on poorly studied North American plant distributions extending into southern Mexico.