Athyrium 



POLYPODIACEAE 



51 



50 



Map 25 



Athyrium thelypteroides (Michx.) Desv 



8. ATHYRIUM Roth 



[Butters. The genus Athyrium and the North American ferns allied to 

 Athyrium Filix-femina. Rhodora 19 : 170-197. 1917. Pinkerton. Ferns of 

 Missouri. Ann. Missouri Bot. Gard. 20 : 54-57. 1933.] 



Fronds pinnate. 



Pinnae entire ^ A - pycnocarpon. 



Pinnae deeply pinnatifid 2. A. acrostichoides. 



Fronds bipinnate. 



Rhizomes creeping, not densely covered with persistent bases of old fronds; stipe 

 usually about as long as the blade; scales of stipes very few, rarely persistent, 

 yellowish brown or tawny; blades widest near the base; young indusia with 



glandular cilia; spores somewhat nigrescent, wrinkled 3. A. asplenioides. 



Rhizomes horizontal, completely concealed by thick, fleshy bases of old fronds; stipe 

 about half as long as the blade; scales of stipes varying from Mars Brown 

 (Ridgway Standard) to nearly black; blades widest near the middle, the lower 

 pinnae shorter and often deflexed ; indusia toothed or short-ciliate, never glandu- 

 lar; spores yellow, smooth or slightly papillate. 

 Sori confluent at maturity and usually covering the lower side of the fertile 

 pinnules; fertile frond contracted. 

 Longest pinnae of fertile frond 5-12 cm long; pinnules 4-12 mm long; pinnules 

 of sterile fronds oblong, obtuse, slightly toothed or lobed. . .4. A. angustum. 

 Longest pinnae of fertile frond 1-2 dm long; pinnules 12-25 mm long, pinnatifid; 

 sori several on each of the lower segments, often horseshoe-shaped; pinnules 

 of sterile fronds oblong-lanceolate, strongly toothed or pinnatifid, some- 

 what acute 4a. A. angustum var. elatius. 



Sori usually separate and distinct at maturity; fertile fronds not contracted; 

 pinnules lanceolate, subacute, strongly toothed or pinnatifid, the segments 

 toothed 4b. A. angustum var. rubellum. 



1. Athyrium pycnocarpon (Spreng.) Tidestr. (Asplenium angustifol- 

 ium Michx. and Asplenium pycnocarpon Spreng.) Narrowleaf Spleen- 

 WORT. Map 24. Infrequent to frequent in southern Indiana, becoming less 

 frequent to rare northward. It prefers deep humus and is most commonly 

 found on the slopes of ravines in beech woods. 



W. Que to Wis., southw. to Ga., Ala., Mo., and Kans. 



