Piedraia hortae is a superficial fungus that exists in the soils of tropical and subtropical environments and affects both sexes of all ages. The fungus grows very slowly, forming dark hyphae, which contain chlamydoconidia cells and black colonies when grown on agar. Piedraia hortae is a dermatophyte and causes a superficial fungal infection known as black piedra, which causes the formation of black nodules on the hair shaft and leads to progressive weakening of the hair. The infection usually infects hairs on the scalp and beard, but other varieties tend to grow on pubic hairs. The infection is usually treated with cutting or shaving of the hair and followed by the application of anti-fungal and topical agents. The fungus is used for cosmetic purposes to darken hair in some societies as a symbol of attractiveness. Morphology
When grown on agar at 25 °C (77 °F) Piedraia hortae grows very slowly to form black-greenish, limited and pointed colonies. Piedraia hortae taken from infected hairs have dark brown nodules, which are made up of ascostroma. The nodules have a gritty feel, organized in a stromatic fashion and have a high concentration of chitin and melanoid pigments. The colonies produce a red pigment and remain smooth and covered with short aerial hyphae. Microscopically, P. hortae produces short, dark hyphae containing thick-walled resting cells. The ascomata consist of irregularly shaped pseudothecia that are black in colour. Each ascoma contains a single ascus containing eight ascospores. The ascospores are dark, curved and become very narrow at the ends forming whip-like appendages.
Black piedra usually affects scalp hair, whereas white piedra is more commonly found in pubic hair, axillary hair, beards, moustaches, and eyelashes. White piedra affects horses and monkeys, in addition to humans and the nodules are white and brown in colour and can be easily detached from the hair shaft. White piedra is treated by using topical and antifungal agents, but a more effective approach is to use itraconazole therapy. Recent studies have shown that the black, lichen-colonizing fungus, Xanthoriicola physciae, is closely related to P. hortae. See also
White piedra
Piedra

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