The Breeding System of Lithospermum caroliniense: Adaptation and Counteradaptation

Abstract

The breeding system of the perennial herb Lithospermum caroliniense was analyzed in a population located near Zion, Lake County, Illinois. The species is both heterostylic and functionally cleistogamic, its populations containing plants which are solely chasmogamic, solely cleistogamic, or partially cleistogamic. Heterostyly is accompanied by pollen dimorphism so that levels of legitimate pollen flow may be accurately measured by examining stigmas and noting the size of the legitimate pollen loads. Legitimate pollen flow was measured at Zion, and it was found that 63% of the pin stigmas bore legitimate grains as compared with 42% of the thrum stigmas. The average numbers of such grains on all pin and thrum stigmas were 4.88 and 2.75, respectively, the range being one to 45 in the former and one to 43 in the latter. The distribution of legitimate loads on both stigmas was markedly leptokurtic. Average pollen loads per plant were related to the proximity of legitimate pollen donor. Illegitimate loads ranged...