Floral Morphology Nectar Production And Breeding Systems In Dudleya Subgenus Dudleya Crassulaceae

Floral morphology, nectar production, and breeding systems of 2 1 taxa in Dudleya subgenus Dudleya suggest three reproductive strategies. Most species-13 of those examined -have 1-1 5% auto-fertility (defined as the proportion of seed set by self-pollination in the absence of pollinators) and produce nectar with about 2-5 mg sugar per flower. These species, which are predominantly coastal in distribution, have dense inflorescences of yellow flowers and appear to be pollinated primarily by bees and long-tongued flies. Increased seed set and seedling vigor with cross-pollination select for outcrossing in these species. A second group of three species has long-tubed, frequently pendent, red flowers in very open cymes, high auto-fertility (about 40-60%), and abundant nectar-yielding 5-12 mg sugar/flower. Ranging from hills near the coast to desert mountains, these species are hummingbirdpollinated. The remaining three species (one with three subspecies) have short-tubed flowers in dense cymes, high auto-fertility (25-50%), and nectar production of less than 2.5 mg sugar/flower. These species are typically montane and occupy habitats with shorter and less reliable growing seasons than are usual for the genus. Environmental unpredictability and pollinator unreliability may explain the apparent trend toward autogamy in the third group and the high auto-fertility of the hummingbirdpollinated species. Because flowers are protandrous, even species with high auto-fertility maintain the ability to outcross if pollinators are available. ' Although Johansen (1935) reported that flowers of Z). echeverioides. now regarded as a synonym of D. greenei, have an odor resembling woodland violets, neither we nor Moran (1951) has been able to detect any floral fragrance in D. greenei.