The evolution of self-pollination in granite outcrop species of Arenaria ( Caryophyllaceae). I. Morphological correlates.

Abstract

Two very closely related species of Arenaria are endemic to granite outcrops in the SE USA: the widespread, outcrossing A. uniflora and the rare, selfing A. alabamensis. A survey of 9 populations showed a wide range of variation in degree of protandry, which correlated closely with levels of spontaneous fruit-set in the absence of insect pollinators. Highly distinctive differences among populations for 11 floral characters were maintained under uniform growing conditions in a greenhouse. The characters also varied little between years. Strongly protandrous populations had larger petals, stamens, and styles than homogamous ones, a trend consistent with selfers often showing reduction or loss of features associated with the attraction of pollinators. Analysis of 7 vegetative characters, however, showed clinal geographical patterns, unrelated to variation in the breeding system. Self-pollinating morphs may have evolved independently at least twice at the margins of the range of A. uniflora. -from Author