Flora of North America species comparison

In accord with the most recent revision (R. M. Tryon 1941) of the genus, Pteridium is treated here as a single widespread species composed of two subspecies with 12 varieties. So treated, it is probably the most widespread species of all vascular plants, with the exception of a few annual weeds (F. H. Perring and B. G. Gardner 1976). The plants are generally aggressive, invading disturbed areas as weeds in pastures, cultivated fields, and roadsides. In Europe, it was harvested and burned to produce potash. Although croziers are eaten in many temperate cultures, bracken has been shown to contain thiaminase (and other compounds with mutagenic and carcinogenic properties).

Disagreement exists among taxonomists regarding the rank that should be accorded to the taxa treated herein as varieties. In a survey of the genus, C. N. Page (1976) noted uniform chromosome numbers and flavonoid compositions of the varieties. D. B. Lellinger (1985) separated the genus into at least two species based on morphology, recognizing as species the subspecies of R. M. Tryon (1941). J. T. Mickel and J. M. Beitel (1988) reported sympatric occurrence in Mexico of three taxa that maintained consistent characteristics and only rarely produced plants with combined characteristics. They suggested that these three taxa should be considered as species that occasionally hybridize. P. J. Brownsey (1989) reported that two different brackens in Australia formed sterile hybrids and should be treated as species. Modern systematic studies are needed to evaluate the status and rank of the four North American varieties. As treated below, Pteridium aquilinum var. pubescens, var. latiusculum, and var. pseudocaudatum are in subsp. aquilinum, and var. caudatum is in subsp. caudatum (Linnaeus) Bonaparte.

Varieties 12 (4 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The family is variously circumscribed, in the strict sense including only eight genera, while in the broadest sense encompassing about half the recognized genera of higher ferns (R. E. Holttum 1947). Here it is delimited in the sense of J. T. Mickel (1973). Characteristics that define the family include submarginal or marginal sori with generally two indusia, an inner true indusium and an outer false indusium formed by the revolute, often modified segment margin (although either type may be reduced or absent in some genera); indument usually of hairs rather than scales; and long-creeping protostelic or solenostelic stems with stem buds on the bases of the petioles. Not all genera in the family share all the characteristics.

Genera ca. 20, species perhaps 400 (4 genera, 6 species in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)