Effect of pollen limitation, additional nutrients, flower position and flowering phenology on fruit and seed production in Salvia verbenaca (Lamiaceae)

Variation in fruit set, seed/ovule ratio and mean single-seed weight among plants, and within plants among inflorescences, was investigated in a population of Salvia verbenaca in northwest Spain. Mean single-seed weight varied significantly among plants which flowered at about the same time and mean single-seed weight was significantly greater for plants that flowered late in the season than for plants flowering early in the season. Within individual plants, mean single-seed weight increased steadily between the earlier opening basal inflorescences and the later opening upper inflorescences. However, neither fruit set nor seed/ovule ratio varied significantly among inflorescences. Previous work on this population indicates that outcrossing improves mean single-seed weight, so I suggest that the observed pattern of among-inflorescence variation in mean single-seed weight may be attributable to a gradual increase in nonself pollen receipt as the flowering season progresses.