1,^^ TRANSACTIONS ^ OF THE SAN DIEGO SOCIETY OF NATURAL HISTORY Volume 21 Number 3 pp. 57-70 29 October 1985 L/eRARy Floral morphology, nectar production, and breeding systems in Dudleya subgenus Dudleya (Crassulaceae) Geoffrey A. Levin L* --Department of Botany, San Diego Hatuml Historv Kf^eum, San Diego, California 92112 USA Thomas W. Mulroy URS Company, HI W. Micheltorena, 3rd Floor, Santa Barbara, California 93101 USA Abstract. 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 hummingbird-pollinated. 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 hummingbird-pollinated species. Because flowers are protandrous, even species with high auto-fertility maintain the ability to outcross if pollinators are available. Introduction The genus Dudleya (Crassulaceae) consists of about 40 species of succulent rosette perennials of western North America (Moran 1951, 1959). Subgenus Dudleya is the most diverse (about 25 species) and most widespread of the three subgenera. The greatest diversity is in coastal and insular southern California and Baja California, although the subgenus extends from the Cape Region of Baja California to coastal southern Oregon and inland to southern Nevada and central Arizona, spanning an altitudinal range from sea level to 2750 m. Habitats include coastal bluffs, montane canyons, and slopes of desert mountains. About half the species are narrow endemics, many of them insular; the remainder are widespread. Except in a few species of coastal northern Baja California, distributions are mostly patchy, with populations commonly small and well isolated. Given the great diversity of habitat and population structure of its species, Dudleya might be expected to vary in 1) breeding systems, 2) pollination syndromes, and 3) reproductive strategies. Some aspects of pollination biology have been shown to vary within groups of related plants, e.g., at the family level in Polemoniaceae (Grant and Grant 1965) and Bignoniaceae (Gentry 1 974), and at the generic level in Agave (Schaffer and Schaffer 1977), Leavenworthia (Lloyd 1965, Solbrig 1976, Solbrig and Rollins 1977), Pedicularis (Sprague 1962, Macior 1968, 1970), Rhododendron (Stevens 1976) and Trichostema (Spira 1980). Yet, except in Spira's study, variation in all three aspects has not been examined in a single genus.
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