Circumscription of the South American Moonwort Botrychium (Ophioglossaceae)

Abstract

The genus Botrychium (Ophioglossaceae) is comprised of about 30 widely distributed species. Because of their small size and few, yet variable, morphological characters, many questionable taxa have been described over the years. Since its description in 1906, B. dusenii has been treated as both a distinct species and variously divided into four taxa: B. lunaria var. dusenii, B. lunaria var. antarctica, B. ramosum var. patagonicum, and B. matricariifolium subsp. patagonica. The aim of this study is to evaluate the validity of these taxa using spore wall sculpture, spore size, allelic composition employing enzyme electrophoresis, and morphological characters. We conclude that only one species of Botrychium occurs in the study area and recognize this as B. dusenii, a species distinct from B. lunaria. Enzyme electrophoresis and spore size suggest that B. dusenii is an allotetraploid derived through hybridization between a diploid member of B. lunaria complex and a diploid member of the B. campestre complex. We provide information about habitat, distribution, and full exsiccate citations.