26 Karl M. Wiegand and Arthur J. Eames 



Division I. PTERIDOPHYTA 



1. POLYPODIACEAE (Fern Family) - 



Artificial Key to the Genera 



a. Sori (with indusia) inclosed in globular or necklace-like parts of the much- 

 modified and contracted fertile fronds. 

 b. Sterile fronds 1-pinnatifid; veins netted; fertile fronds 2-pinnate ; rootstocks 



creeping. 3 4. Onoclea 



b. Sterile fronds 2-pinnatifid ; veins free ; fertile fronds 1-pinnate ; rootstocks 

 short, erect. 3. Pteretis 



a. Sori exposed or simply covered by the reflexed margin of the frond. 



b. Sori marginal, the indusium appearing to consist of the reflexed margin of the 

 frond ; rootstocks creeping. 

 c. Sorus apparently continuous along the whole margin. 

 d. Fronds very large, broadly triangular, 1-3-pinnate. 15. Pteridium 



d. Fronds small, ovate-oblong. 



c. Fronds delicate, membranous. . 13. Cryptogram ma 



c. Fronds coriaceous. 12. Pellaea ' 



c. Sori several or many, distinct. 

 d. Sori sublimate, at the tips of the fan-shaped pinnules ; fronds pedate. 



14. Adiantpm 

 d. Sori as broad as long, marginal or partly covered by a reflexed tooth of the 

 incised pinnule in addition to the true cup-shaped indusium ; fronds 

 2-pinnate. 7. Dennstaedtia 



b. Sori dorsal, though sometimes near the margin ; indusium independent of the 

 margin of the frond. 

 c. Sori elongated. 



d. Veins free except the lowest, the tips not anastomosing ; fronds 1-2-pinnate. 



e. Sori semi-elliptical or some of them horseshoe-like, attached to the lateral 



veins only ; rootstocks not creeping. 



/. Indusium straight; fronds 1-pinnate, with black stipes; xylem in cross 



section of stipe X-, Y-, or T-shaped, or of two strands, the edges of 



the plates toward the upper side of the stipe not inflexed ; cells of the 



scales rectangular, with thick, dark walls ; small evergreen ferns. 



10. Asplenium 

 /. Indusium straight or horseshoe-shaped ; fronds 1-2-pinnate, with pale 

 stipes ; xylem V-shaped or of two strands, the edges of the plates 

 toward the upper side of the stipe strongly inflexed; cells of the scales 

 more acute or fibrous-tipped, thinner and paler-walled ; larger her- 

 baceous ferns. 8. Athyrium 

 c. Sori oblong or linear, extending along both the lateral veins and the 

 midrib of the pinnae; rootstocks creeping. 11. Woodwardia 

 d. Veins netted ; fronds lanceolate, undivided, rooting at the slender tip ; sori 

 variously disposed. 9. Camptosorus 

 c. Sori orbicular or nearly so. 



d. Indusium superficial or wanting; fronds often evergreen. 



c. Fronds articulated with the creeping rootstocks, 1-pinnatifid, the divisions 



confluent at the base; sori naked. 16. Polypodium 



c. Fronds not articulate, 1-3-pinnate, if 1-pinnate the divisions distinct; 

 rootstocks creeping or not creeping ; sori naked or covered. 

 /. Indusium cordate or wanting; pinnae pinnatifid or pinnate. 



5. Thelypteris 



2 For changes in the nomenclature of the ferns, see Rhodora, vol. 21, p. 173, 1919. 



3 Ferns with creeping rootstocks have scattered fronds; those with short or upright rootstocks 

 have the fronds in clusters. 



