7. Sori not borne on the under surface of a recurved marginal lobule but on the 



leaf surface under a recurved marginal lobule (when this is pres- 

 ent) (8) 



8(7). Sori linear-elliptic; indusia curved and crescentiform 5. Athyrium 



8. Sori round; indusia not curved or crescentiform (9) 



9(8). Acicular unicellular hairs present on the costae above; segments of the 

 fronds ciliate; stipe bundles 2, these united below the base of the 

 blade; rhizome scales ciliate (sometimes sparingly so); rhizomes 

 slender, mostly creeping; fronds membranous, mostly deciduous; 

 veins reaching the margin 6. Thelypteris 



9. Acicular hairs absent on the costae above; segments of the fronds not ciliate; 



stipe bundles 3 to 7, free to above the base of the blade; rhizome 

 scales not ciliate, sometimes toothed; rhizomes massive, short- 

 creeping to erect; fronds herbaceous to coriaceous, sometimes ever- 

 green; veins ending short of the margin in elongate hydathodes 



7. Dryopteris 



1. Adiantum L. Maidenhair Fern 



Delicate terrestrial or rock-inhabiting plants of moist wooded slopes, ravines 

 and stream banks, with slender creeping to short and ascending scaly rhizomes; 

 fronds suberect to pendent, distichous or in several ranks; stipes slender, strong, 

 usually blackish and lustrous, glabrous or rarely pubescent, scaly at base only; 

 blades pedately or pinnately decompound, variously dissected, rarely simple; ulti- 

 mate segments oblique, petiolate or subsessile, articulate and deciduous in some 

 species, membranous to subcoriaceous, mostly glabrous, with veins free and 

 forking or rarely anastomosing; sori borne along or rarely between the ends of 

 the ultimate veins, appearing marginal on the back of the reflexed apex of the 

 lobules of the pinnules or ultimate segments; indusia formed in part by the re- 

 flexed margins of the lobules. 



About 200 species, mainly in tropical America. Many species are cultivated. 



1. Fronds smooth; ultimate segments obovate-cuneate or rhombic, usually promi- 

 nently incised 1. A. Capillus-Veneris. 



1. Fronds pilose with whitish hairs; ultimate segments suborbicular, not promi- 

 nently incised 2. A. tricholepis. 



1. Adiantum Capillus-Veneris L. Culantrillo. Fig. 14. 



Rhizomes horizontal, creeping, cordlike, laxly scaly; rhizome scales thin, light- 

 brown, hnear-lanceolate, attenuate, entire; fronds numerous, clustered or scattered 

 along the rhizome, laxly ascending to pendulous, 13-7 dm. tall; stipes reddish- 

 brown to purplish-black, lustrous, sulcate, glabrous, mostly shorter than the 

 blades; blades broadly ovate to lanceolate, attenuate at apex, bipinnate to tripinnate 

 or occasionally quadripinnate, glabrous, 1.5-4 dm. long, to 3.5 dm. wide; pinnae 

 alternate, laxly spreading, petiolate, to 18 cm. long; ultimate segments numerous, 

 petiolulate, not jointed, membranous to thin-herbaceous, bright-green, variable in 

 size and shape, obliquely obovate to semiorbicular, truncate to obliquely cuneate 

 at the base, the outer margin more or less incised or deeply lobulate, 7-30 mm. 

 long, about as wide as long; sterile segments regularly denticulate with the teeth 

 acute to long-acuminate; sori borne on the margins of the lobules of the ultimate 

 segments, somewhat lunate; modified indusial margin of the lobules glabrous, 

 prominent, scarious, with crenate margins. A. modestum Underw., A. tricholepis 

 f. glabrum Clute. 



Limestone rocks, ledges and cliffs, especially along streams and about pools in 

 canyons and ravines, rare in Okla., in Tex. frequent on the Edwards Plateau and 

 in the Trans-Pecos, e. to Harris Co. on the Coastal Plain and s.w. to Zavala Co. in 



63 



