1. Pteridium aquilinum (L.) Kuhn (bracken) Pl. 3a,b,c;
Map 13
Leaves 35–150 cm long (to 4 m, elsewhere). Petioles straw-colored to light
brown. Leaf blades 2–3 times pinnately compound, the pinnules lobed, broadly
triangular in outline, with slender hairs along the upper surface margins and
the undersurface midribs or nearly glabrous. Sori in a nearly continuous line
along the pinnule margins, the indusia poorly developed, hidden by the recurved
pinnule margins. Spores trilete, 23–39 mm in diameter, light brown. July–September.
Scattered in the southern half of the state, mostly in the Ozarks, and locally
north to Sullivan County (nearly worldwide). Openings of rocky, upland forests
and road banks, mostly in acid soils.
Collectively, Pteridium aquilinum is one of the most broadly distributed
species of vascular plants of the world. In many parts of its range it is
considered a noxious weed that spreads with disturbance of the environment.
Toxins contained in the leaves inhibit the growth of other plant species, and
bracken fern has been shown to interfere with the regeneration of trees and
shrubs following fires or logging in the western United States. The leaves also
contain substances that are poisonous to livestock and humans when eaten.
Although the young fiddleheads are still consumed in Japanese and other
cuisines, they have been shown to contain a number of nerve poisons as well as
carcinogenic and mutagenic compounds and have been implicated in increased
rates of intestinal tumors in regions where they are a common part of the diet
(Hodge, 1973).
Pteridium aquilinum has been used in a variety of other ways in various
parts of the world. The leaves have been used for packing material and
thatching and have also been burned for the production of potash. Bracken is
also among the largest of fern species. Studies by Sheffield et al. (1989)
suggest that rhizomes may grow to more than 390 m long.
Of the 12 varieties, 2 occur in Missouri. Both of these are assignable to ssp. aquilinum,
and there is considerable intergradation between them.