REPRODUCTIVE PROFICIENCY IN PAEONIA CALIFORNICA (PAEONIACEAE)

Abstract

Study of three populations of geophytic Paeonia californica in southern California revealed considerable variation, within and between populations, in both potential and in realized seed output. Plants are weakly self‐compatible, but natural seed set (x = 4.2 seeds per carpel) is closer to seed set produced in hand cross‐pollinations (x = 4.5) than in self pollinations (x = 1.4). Flowers are protogynous, nectariferous, and scented; 17 species of bees in four families, and one species of melyrid beetle were found in them and probably account for pollinations at these sites. Counts of reproductive parts show greatest inter‐population variation in mean numbers per plant, of flowers (population means ranged from 16.2 to 21.2), ovules (744 to 1142), pollen grains (23 million to 38 million), and % viable pollen (26.6 to 81.4). Seed set also varied significantly, with only 11.4 to 26.8 % of the ovules maturing into seeds. This low reproductive success is probably correlated with the genetic anomalies studied by others—particularly the translocation heterozygosity that causes lowered production of viable gametes. The relatively few seeds produced are heavy (x = 0.184 g per seed), and germination percentages are high (x = 80%). The elongation of cotyledon bases during hypogeal germination seems to permit optimal germination at soil depths of only 2–3 cm, but environmental factors such as drought stress and herbivore pressure promote high seedling mortality.