Cystotheca lanestris
Cystotheca lanestris is a species of powdery mildew in the family Erysiphaceae. It is found in North America on plants in the genus Quercus. Its primary range is south-western United States and north-western Mexico, mostly along the coast where its preferred host plants are found.
Description
Cystotheca lanestris forms white mycelium turning grey to tan brown with age. It induces witch's-broom galls – abnormal clusters of shoots that are thickened, elongated and highly branched with very small leaves. Cystotheca ''lanestris, like most Erysiphaceae, is fairly host-specific and only infects species in the genus Quercus. Within this genus however, it is found on a rather large selection of oak species, including Quercus agrifolia, alba, bicolor, canbyi, cerris, chrysolepis, coccinea, crassipes, douglasii, engelmannii, garryana, ilex, kelloggii, laceyi, laeta, laurifolia, lobata, macrocarpa, michauxii, nigra, obtusata, palmeri, palustris, phellos, polymorpha, potosina, robur, rubra, stellata, suber, toumeyi, velutina, virginiana, and wislizeni. Asian collections previously assigned to this species belong to a phylogenetically different species, C. kusanoi. Another species infecting Quercus in North America, Cystotheca mexicana'', is endemic to Mexico and is found on similarly endemic oaks.
Taxonomy
The fungus was formally described in 1884 by Harkness with the basionym Sphaerotheca lanestris. The species was transferred to the genus Cystotheca in 1909 by Miyabe.