Intraspecific Variation in Seed Morphology of Arenaria uniflora (Caryophyllaceae)

Intraspecific variation in seed morphology was analyzed by SEM for nine popula- tions of Arenaria uniflora, a winter annual endemic to rock outcrops in the southeastern United States. Seed lengths ranged from 0.47-0.58 mm and showed almost no overlap between populations. Seed coats varied from corrugate surfaces with sinuate cell margins in plants from the center of the range in Georgia to smooth surfaces with entire cell margins for plants from the peripheries of the distribution in Alabama and the Carolinas. Rough, thick seed coats were characteristic of dry sites, and smooth, thin seed coats, of wet sites. Germination of smooth seeds occurred most rapidly, while more corrugate seeds required progressively longer to reach similar germination percentages. The wide range of variation detected in A. uniflora is probably due to the high potential for local differentiation of populations isolated on rock outcrops. The high levels of intraspecific variation reported here suggest that caution should be used whenever SEM-level features are employed to characterize species or other taxa.