Elevation of Three Varieties of the Malagasy Endemic Casearia nigrescens (Salicaceae) to the Species Level

Abstract

The Malagasy species of Casearia Jacq. (Salicaceae) have no modern taxonomic treatment and present particular difficulties due to their similar flowers. Twentieth-century authors have adopted overly lumping classifications featuring broad circumscriptions of C. nigrescens Tul. Perrier de la Bâthie published three varieties within C. nigrescens sensu Tulasne: varieties onivensis H. Perrier, ovata H. Perrier, and subtrinervia H. Perrier. All of these are from eastern humid forests, farther inland and at higher elevations than is typical of variety nigrescens s. str. Study of the available specimens indicates that all are sufficiently distinct from variety nigrescens that they should be elevated to the rank of species. They are herein recognized as C. onivensis (H. Perrier) Ang. X. Wang & Philpott, C. angustifructa Ang. X. Wang & Appleq., and C. subtrinervia (H. Perrier) Ang. X. Wang & Appleq., respectively. All are rarely collected, and preliminary assessment of their conservation status suggests that all three are Endangered.