Systematics of the Cyclanthaceae, especially Sphaeradenia and Chorigyne
During a survey of specimens intended for my revision of Sphaeradenia, it became evident to me that a group of Central American taxa deviated considerably from the rest of the material in several characters. Further studies showed that this group of species is best treated as a separate genus. Accordingly, I established Chorigyne (Eriksson 1989), with two species transferred from Sphaeradenia (Ch. ensiformis and Ch. pendula) and five described as new (Ch. cylindrica, Ch. densiflora, Ch. paucinervis, Ch. pterophylla, and Ch. tumescens). A phylogenetic analysis supports the position of Chorigyne as the monophyletic sister-group to the genus Stelestylis (Eriksson 1994b).
Chorigyne is characterized by free pistillate flowers, four subapical placentas that are confluent at later stages, indehiscent separate fruits, and a seed coat where the cells of several layers of the outer integument become enlarged (Eriksson 1989, 1994b). Distinctly asymmetrical staminate flowers without adaxial perianth lobes and fusiform seeds are shared with Stelestylis. Characteristic is also the presence of anthers with secretion globules, a derived state that has evolved in the ancestor common to Chorigyne, Stelestylis, and Sphaeradenia, but which is polymorphic in the two latter genera.
Chorigyne is restricted to Costa Rica and Panama, an area to which its ancestor probably migrated from northwestern South America during the formation of a land connection across the Isthmus of Panama, or soon after the connection was completed, in Pliocene (Eriksson 1989). The differentiation of Chorigyne is consequently a rather recent event.
Maintained by Roger Eriksson and last updated August 17, 2006.