THE REPRODUCTIVE SYSTEM OF JEPSONIA HETERANDRA.

Abstract

A century ago, the biological significance of heterostyly began to be investigated by workers as Darwin (1862) and Hildebrand (1864). As a result of these studies and more recent ones, subsequent workers generally have accepted the explanation that the reciprocal position of anthers and stigmas in heterostylous flowers is associated with an outcrossing mechanism mediated by pollinators. Although this functional interpretation of heterostyly has been accepted widely, there are few studies of the pollination biology of heterostylous plant species. The purpose of this paper is to present the results of a study of the reproductive system of Jepsonia heterandra Eastw. (Saxifragaceae), a self-incompatible heterostylous perennial herb that is endemic to a small area in California (Ornduff, 1961, 1969). A major concern of this report is a documentation of the floral morphology, population structure, incompatibility system, and mode of pollination of J. heterandra. The investigation was aimed at determining whether or not heterostyly influences pollen transfer according to the expectations that are based on the positional relationships of anthers and stigmas. In addition the study was concerned with establishing the presence of an incompatibility system and the relation of this system to the floral heteromorphism. Another objective was determining whether floral heteromorphism and an incompatibility system operate synergetically in conjunction with a pollination system that is mediated by insect visitors. This last point is of special importance because the origin, maintenance, and functional interpretation of floral heteromorphism all depend upon the behavior patterns of the pollinator fauna in relation to the phenology and floral morphology of the plants under study. Except where noted, the observations described in the text and tables in this paper were made on a population of J. heterandra located along Rock Creek Road, between Milton and the Salt Springs Reservoir, Calaveras County, California.