FERN FAMILY 



23 



12. PTERIDIUM Scop. FI. Carn. 169. 1760. 



Coarse ferns of open or partially shaded, acid-soil situation?, the slender, woody, freely 



branched rhizome wide-creeping underground. Fronds stout, erect to reclining, up to 5 



meters long, borne singly, the stout stipes with a feltlike covering at the base, not jointed to 



the rhizome; blades large, triangular or deltoid-ovate to elongate, pinnately decompound, 



the ultimate segments entire, toothed, or lobed. Sori linear, marginal, continuous, arising 



from a transverse veinlike receptacle connecting the ends of the forked free veins ; indusium 



double, the outer one prominent, formed by the reflexed membranous margin of the blade, 



the inner obscure, delicate, usually minute, borne upon the receptacle, nearly concealed by 



the sporangia, and facing outward. [Diminutive of Ptcris, the ancient Greek name of ferns.] 



Six or eight widely distributed species, three or four occurring in other parts of North America. Type 

 species, Pteris aquilina L. ' 



1. Pteridium aquilinum pubescens Underw. 

 Western Bracken. Vig. 43. 



Ptcris feci Schaffn. ; Fee, Mem. Foug. 8: 73. 1837. 



Pteridium aqiiiliniiin pubescens Underw. Nat. Ferns ed. 6, 91. 

 1900. 



Stipes erect, stout, stramineous from a darker base, 

 15-100 cm. long; blades oblique, deltoid to deltoid- 

 ovate, 25-100 cm. long, subternately decompound, usually 

 3-pinnate in the basal part ; segments variable, linear- 

 oblong and entire, to hastate or deltoid-oblong and 

 pinnatifid, often dilatate, rigidly herbaceous, pubescent 

 or strongly sericeous-tomentose beneath, slightly hairy 

 or glabrous above ; indusia usually narrow, villous, but 

 not often truly ciliate. 



Moist woods and thickets or dry open slopes, Alaska to 

 Montana, southward to Mexico. Type locality: not definitely 

 stated. E.xtremely variable in stature and in nearly all technical 

 characters, these mostly correlated with habitat. A few speci- 

 mens approach the typical European form. 



13. ADIANTUM [Tourn.] L. Sp. PI. 1094. 1753. 



Delicate graceful ferns of nijoist rocky woods and ravines, with thickish suberect to 

 slender wide-creeping, paleaceous rhizomes. Fronds distichous or in several ranks, rigidly 

 ascending to drooping, the stipes finn, dark, usually lustrous ; blades simple, 1-3-pinnate, 

 or decompound, usually with dark, polislied rachises, extremely variable according to fer- 

 tility, the pinnules glabrous or variously pubescent, sessile or stalked, often articulate, 

 readily deciduous in many species. Sori appearing marginal, the sporangia borne along and 

 sometimes between tlic ends of the free forking veins, on the under side of sharply reflexed 

 indusiform marginal lobes of the pinnules or segments. [The ancient naine. in allusion to 

 the pinnae repelling rain-drops.] 



About 200 species, largely tropical American. In addition to the following, four species occur in other 

 parts of the United States. Type species, Adianfum capillus-reneris L. 



Blades reniform-orbicular, the two equal divisions spreading, with unilaterally arranged pinnate branches. 



1. A. pedatuin aleuticum. 

 Blades elongate, with a continuous main rachis. 



Fronds erect; pinnules roundish or semicircular, slightly lobed; sori mostly linear, straight or arcuate. 



2. A. jordani. 



tronds laxly ascending or drooping; pinnules cuneate-obovate to rhombic, deeply incised; sori mostly 

 oblong-lunate. 3. A. capiUus-ieneris. 



