Non-Twining Milkweed Vines of Oklahoma: An Overview of Matelea biflora and Matelea cynanchoides (Apocynaceae)

Matelea (Apocynaceae, Asclepiadoideae) is a genus of approximately 225 species in milkweed subtribe Gonolobinae. This New World genus is predominantly found in tropical to subtropical regions and is represented in Oklahoma by four species. Two of these, M. biflora and M. cynanchoides, are closely related, non-twining perennial herbs that have long confused amateur and professional botanists alike due to similar morphological features. This paper includes a brief review of their taxonomic history and describes the morphology, ecology, and distribution of these species in Oklahoma and neighboring states. Photographs, a distribution map, and a key to the species of Matelea in Oklahoma are included.