Discussion

Dudleya pulverulenta is one of the largest and most distinctive species of the genus, easily recognized from a distance, even without flowers. All parts of the flowering shoot often are farinose. It has the widest range of any dudleya, over 1000 kilometers, from Monterey County to the Sierra San Borja in north-central Baja California. It is a beautiful plant, much admired but less easily grown than some others. Hummingbirds often visit Dudleya pulverulenta, hovering beneath the pendent flowers and thrusting their bills up into them for nectar. The species shows a syndrome of traits that K. A. Grant and V. Grant (1968) found in hummingbird-pollinated plants of western North America: open inflorescence; pendent flowers on long, slender pedicels; long red corolla with long tube; and (as shown by G. A. Levin and T. W. Mulroy 1985) high nectar yield. Although hummingbirds also visit other species of the genus, this one seems especially adapted to them as pollinators, having, for example, about the longest corolla, with the longest tube, and the highest nectar output. While most other dudleyas have flowers erect along the adaxial side of the cincinnal branch, here the young branch twists at the base, putting the flowers on the abaxial or outer side, where they are declined or pendent. After flowering, each pedicel bends sharply to bring the fruit erect, as it is in other species. This syndrome is nearly unique to D. pulverulenta and the related D. anthonyi, of northern Baja California, although variously approached in forms of the related and intergrading D. arizonica. 10c. Dudleya Britton & Rose subg. Hasseanthus (Rose) Moran, Leafl. W. Bot. 7: 110. 1953 Hasseanthus Rose in N. L. Britton and J. N. Rose, New N. Amer. Crassul., 37. 1903 The underground corms of subg. Hasseanthus, and the leaves that wither in spring, seem clear adaptations to drought. Also, the plants are reduced in size and in lifespan. M. Dodero (1996) found that in the greenhouse the smaller ones could flower in five months from seed. From morphological and allozyme data, he concluded that the group is monophyletic, seeming close to Dudleya attenuata, the species of subg. Stylophyllum with the most-reduced leaves and inflorescence. He suggested that by paedomorphosis the underground caudex (“corm”) probably evolved from the tuberous caudex he noted in Dudleya seedlings, which furthermore tend to be drought-deciduous, and that the leaves became smaller, with narrower and thinner petioles, as in the series from D. multicaulis through D. variegata and D. blochmaniae to D. brevifolia. Thus he found the adult leaves of D. brevifolia like the first seedling leaves of these other species. Although in subg. Dudleya and Stylophyllum the leaves rarely become detached and take root, M. Dodero (1996) found that in subg. Hasseanthus they more often do. The leaves readily root at the base and quickly form new plants, most easily in those species with narrower leaf bases. Where wild plants were browsed by rabbits and rodents, he sometimes found detached leaves rooting. In the greenhouse, with species having smaller leaves, he even saw new rosettes formed in January and flowering by April.