Pteridium aquilinum var. latiusculum (Desv.) Underw.

Authority

Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.

Family

Dennstaedtiaceae

Scientific Name

Pteridium aquilinum var. latiusculum (Desv.) A.Heller ex Underw.

Description

Species Description - Adaxial laminar surfaces with scattered hairs, primarily on costae and near segment margins; abaxial costae with lax pale hairs, axes with occasional brown hairs; segments with hairs on costae and on curved adaxial margins but glabrous between costae and margins; indusial margins glabrous; 2n=104 (USA).

Discussion

Pteris latiuscula Desv., Me´m. Soc. Linn. Paris 6: 303. 1827. Type. Canada. Newfoundland and St. Pierre, s. coll. s.n. (P-Desv., photos GH, US).

Most reports of var. pubescens from Mexico are var. latiusculum. Var. latiusculum is distinct from var. pubescens in having glabrous abaxial laminar surfaces except for hairs on the costae and segment margins (but not on indusia). Var. pubescens is distinct from var. latiusculum in its abaxial surfaces densely pubescent between margins and costae vs. only on costae, and the indusia ciliate to pubescent vs. glabrous. It varies from glabrous to sparsely hairy on the laminar tissue abaxially. Var. pubescens, with its straight hairs scattered on the abaxial surfaces, is limited to the Baja California peninsula and extends northward along the coast to Alaska, extending inland across Canada to northern Michigan and widespread in the western United States. Var. latiusculum, besides occurring in eastern North America, is found in the eastern Rockies and also in Arizona and New Mexico. As Tryon (1941) pointed out, in areas of sympatry var. latiusculum and var. pubescens intergrade. Jacobs and Peck (in FNA Ed. Comm., 1993) claimed that in the United States, all Pteridium west of the Great Plains is var. pubescens, and var. latiusculum occurs east of the Great Plains, but not in Mexico