3. Pteridium Gleditsch ex Scopoli, Fl. Carniol. 169. 1760.
[Bracken ferns [Greek pteridion, a small fern]
Carol A. Jacobs
James H. Peck
Plants terrestrial, often forming colonies or thickets. Stems subterranean, slender, long-creeping; hairs pale to dark, jointed; scales absent; true vessels present (absent in other Dennstaedtiaceae genera in the flora). Leaves widely spaced, broadly deltate, 0.5--4.5 m. Petiole glabrous to short-hairy, without prickles, with stem buds near base, vascular bundles numerous, U- or O-shaped in cross section. Blade 2--4-pinnate, rachis and costae grooved adaxially; rachis without prickles; nectaries at base of proximal and sometimes distal pinnae. Segments pinnately divided, ultimate segments ovate to oblong to linear, base extending proximally on costae (decurrent) or proximally (surcurrent), margins entire. Veins free or joined at margin by commissural vein beneath sori, pinnately 2--3-forked. Sori ± continuous, covered by recurved, outer false indusium and obscure, extrorse, inner true indusium. Spores tetrahedral-globose, trilete, very finely granulate. x = 26.
Species 1 (1 species, 4 varieties in the flora): almost worldwide.
SELECTED REFERENCES
Page, C. N. 1976. The taxonomy and phytogeography of bracken---A review. J. Linn. Soc., Bot. 73: 1--34. Perring, F. H. and B. G. Gardener, eds. 1976. The biology of bracken. [Symposium.] J. Linn. Soc., Bot. 73(1--3): i--vi, 1--302. Tryon, R. M. 1941. A revision of the genus Pteridium. Rhodora 43: 1--31, 37--67.
