Pentagramma is a small genus of ferns in the family Pteridaceae, order Polypodiales, native to western North America. The genus comprises approximately six recognised diploid species, all occurring in California and Baja California, with the most widespread species extending northward into British Columbia and eastward into New Mexico and Arizona.
Until 1990, the species now placed in Pentagramma were included in the genus Pityrogramma, and the group's taxonomy has been subject to considerable debate. The genus name and its members have been revised in treatments by Yatskievych, Windham, and Wollenwebber, among others.
The most distinctive morphological feature of Pentagramma is the production of a powdery-waxy deposit called farina on the lower surfaces of the fronds. This whitish or yellowish coating is shared with the related genus Notholaena and other members of the subfamily Cheilanthoideae within Pteridaceae. The fronds are typically pinnate to bipinnate, and the plants grow from scaly rhizomes.
The best-known species is Pentagramma triangularis (goldback fern), whose fronds have a characteristic triangular outline and a pale-golden farina. It is a widespread component of dry, rocky slopes and open woodlands in the California Floristic Province and the Pacific Northwest.
Etymology
The genus name Pentagramma derives from the Greek penta (five) and gramma (line or mark), referring to the five-angled or star-shaped outline of the frond characteristic of several species in the group.
Distribution
All species in Pentagramma are native to the western portions of North America. P. triangularis has the widest range, from British Columbia south through the western United States into Baja California in northwestern Mexico. P. maxonii occurs in New Mexico, Arizona, and the Baja California peninsula. The remaining species are confined to California and Baja California.
Ecology
Pentagramma ferns typically inhabit dry, rocky slopes, chaparral, open woodlands, and canyon walls in Mediterranean-climate regions of the California Floristic Province. The waxy farina on the frond undersurface is thought to help reflect heat and reduce moisture loss, an adaptation suited to seasonally dry environments.
Taxonomy Notes
Pentagramma was segregated from Pityrogramma in 1990 and has since been treated within the subfamily Cheilanthoideae of Pteridaceae. The number of accepted species has varied across treatments; the most recent revision (Schuettpelz and Windham) recognises six diploid species. The genus is placed in order Polypodiales, class Polypodiopsida.
