These rosette succulents are mostly native to California and Baja California, though their range also extends into Oregon and Arizona. Most species are found along the coast or on offshore islands, where they experience regular fog, high humidity, winter rainfall, and summer drought. The few whose range extends inland tolerate greater temperature extremes.
They vary in size from miniature (the Hasseanthus group, with no above ground stem) to medium size (D. brittonii, which can grow to a couple of feet wide). The leaves may or may not have a white powdery dusting. Flowers, which are useful for identification, may be open (flat), closed (tubular) or intermediate, and they attract bees and hummingbirds. Most Dudleyas flower in great abundance once a year when they are thriving.
Dudleyas are excellent container plants and will grow to quite different sizes depending on the size of the container, being dwarfed in small containers and exuberant in larger ones. In mild areas they are very practical landscape plants which require little or no summer irrigation. They are ideally suited to Mediterranean (dry-summer) climates. They do not do well where there is much summer rain, so provide overhead protection at that time of year if necessary. Dudleyas are not recommended as indoor plants unless you can provide hours of sun each day during the winter months.
When potting up Dudleyas, especially the ones that clump, it is important to use top dressing, so the dead leaves do not come in contact with wet soil.
Container Dudleyas require vigilance for the presence of insect pests. Immature inflorescences often attract aphids. The farinaceous species are particularly vulnerable to attack by mealy bugs, because the bugs are camouflaged against the white background. Insect damage to the core may be so severe that the growth point disappears, but much of the time the plant will respond by branching. Distorted leaves may be a warning sign of insect activity in the core.
The 50 or so species of Dudleya can be divided into three subgenera: Hasseanthus (a small group of plants with no above-ground stem), Stylophyllum (plants with open flowers), and Dudleya (plants with tubular or cup-shaped flowers). The greatest number of species are in the latter subgenus. Interestingly, the final 2 subgenera are not actually distinct groups based on DNA studies.
Hasseanthus is quite rare in cultivation. It can be distinguished by a below-ground stem and Sedum-like flowers that open wide at the base. Stylophyllum flowers are also open but midway up the flower, above the calyx. Subgenus Dudleya flowers are closed and roughly tubular but may be spreading at the mouth.
Identification of Dudleyas is complicated by natural variation and the presence of both natural and artificial hybrids. The large, powder-dusted rosettes of D. brittonii, pulverenta, and anthonyi may be tricky to resolve without seeing the flowers. The coastal species D. ingens and the green form of D. brittonii are also tricky to resolve, unless you know the origin.
No Dudleyas outside the Hasseanthus group can be propagated from leaves. That group is said to bloom at 5 months of age with good greenhouse care, and lose its living leaves in the spring. The other plants in the genus may bloom within their first year from seed, provided nursery care.