Gender Modification in North American Ginsengs

Abstract

nly rarely in plants can individuals express either of two distinct genders-one producing ovules, seeds, and fruit and another producing only pollen. Such gender-choosing plants are estimated to comprise 0.1% or less of the angiosperms. Although some reports of gender change are unconvincing, the known gender choosers are a phylogenetically diverse group including both temperate and tropical species (Lloyd and Bawa 1984, Schlessman 1986). The rarity of gender change, or diphasy, cannot be explained by constraints of phylogeny, growth pattern, or climate. In a review of sex change in plants and animals, Policansky (1982) suggested that perhaps no general rules for the evolution of diphasy would be found. He urged biologists to conduct studies that would seek to explain why sex change occurs in some but not other members of small groups of organisms. This article is an attempt to answer that question for the North American species of ginseng (Panax, in the family Araliaceae). The North American ginsengs provide an excellent opportunity to compare a gender chooser with a nonchoosing close relative. Dwarf ginseng (Panax trifolium) exhibits diphasy' (Schlessman 1984). Each individual may switch in either direction