Morphological, Phenological, and Pollen-Distribution Evidence of Autogamy and Xenogamy in Gilia achilleifolia (Polemoniaceae)

Abstract

In three populations of Gilia achilleifoliafloral morphological and phenological characters and pollen distribution on stigmas suggest that different breeding systems are associated with the two main races of the species. The shade race has small corollas, stigmas maturing below the anthers, low pollen production, low pollen-ovule ratios, homogamy, many pollen grains per stigma, and high seed set. The sun race differs in all these characters. Gilia achilleifolia Bentham, including ssp. multicaulis (Bentham) V. & A. Grant, is an annual species endemic to California. It is composed of two races-a race occupying sunny hillsides, characterized by dense inflorescences of large, showy flowers, and a race occupying shady places, having inflorescences with fewer, smaller flowers (Grant, 1954). Evidence for the genetic control of these characters was provided by Grant in a series of reciprocal transplant studies. Flowers of the sun race have stigmas exserted beyond the anthers whereas those of the shade race have stigmas situated below the anthers. Both races are self-compatible, but the progeny of self-pollinated shade-race plants show no inbreeding depression whereas the progeny of self-pollinated sun-race plants are less vigorous than their cross-pollinated counterparts (Grant, 1954). Populations of both races are interspersed throughout the southern and central Coast Ranges (Grant, 1954). While Grant's observations of the flowers and reproductive behavior of plants of the two races of G. achilleifolia led him to postulate that the species is composed of xenogamous and autogamous races, he did not explore this supposition further. In the present study floral characters of populations of the two races, and of a population intermediate between the two, were compared. The characters are: corolla size, degree of stigma exsertion, amount of pollen produced per flower, pollen-ovule ratio, degree of dichogamy, number of pollen grains per stigma, and seed set. MATERIALS AND METHODS The three populations sampled were: a small-flowered population (SML) on the upper slopes of Mt. Diablo in Contra Costa County, a population with intermediate-sized flowers (IMD) in Del Puerto Canyon in Stanislaus County, and a large-flowered population (LGE) in Cerro 'This work was supported in part by a grant from Sigma Xi. I thank Robert Ornduff, Herbert Baker, and Dale Johnson for comments and suggestions. 2 Botany, University of California, Berkeley CA 94720.