short, the upper tooth only slightly curved, lower tooth blunt and shorter than 

 the upper tooth; sori 6 to 11 in each valve. M. vestita of auth. 



Usually in black waxy mud along streams and rivers, in and about ponds, in 

 silt of lakes, and in ditches or depressions such as old buffalo wallows in prairies 

 that are periodically inundated, our most widespread Marsilea occurring through- 

 out Okla. and in every section of Tex. but the Timber Belt, most frequent and 

 abundant in the Blackland Prairies and on the Edwards Plateau, through N.M. 

 (Lea and Sierra cos.) to Ariz. (Navajo, Coconino, Yavapai, Pinal, Cochise and 

 Pima COS.); from s. Sask. and Alta., s. to Tex., N.M., Ariz., Calif, and Coah. e. 

 to Fla. 



Some plants of M. mucronata closely resemble those of M. macropoda, with 

 which they are occasionally confused. The solitary sporocarp, however, readily 

 distinguishes them from that species. 



Although a temporary pool in which this species may occur may become 

 powdery dry in season, the bony sporocarps remain undamaged until water again 

 makes the depression a quagmire. 



4. Marsilea uncinata A. Br. Fig. 9. 



Plants 6-20 cm. tall; rhizomes slender, filiform, producing fascicled branches 

 that are paleaceous at their tips; petioles filiform, to 19 cm. long; leaflets spread- 

 ing, obovate to broadly flabellate, subtruncate to rounded at the apex, entire, to 3 

 cm. long, about as wide as long, glabrous to sparsely strigose-pubescent; peduncles 

 usually attached to the petioles above their base, about twice or more the length 

 of the sporocarps, 1.5-3 cm. long; sporocarps subglobose to ellipsoid, more or less 

 covered by short coarse reddish hairs, 4-8 mm. long, 3-6 mm. in diameter, the 

 raphe long, upper tooth longer than the lower tooth and mostly uncinately 

 curved; sori 13 or 14 in each valve. 



In or on the edge of permanent ponds, along spring branches and in shallow 

 water of brooks, ditches and bayous, rather generally distributed but uncommon 

 in the Blackland Prairies and in several isolated localities in every section of Tex. 

 except the Timber Belt; apparently confined to Tex. and La. 



This species, unlike M. mucronata and M. tenuifolia, apparently needs a con- 

 stant supply of water for optimum development, if not for survival. 



A characteristic that superficially separates this species from the closely allied 

 M. mucronata is the usual attachment of the long peduncle to the leaf petiole 

 above its base. The much shorter peduncle of M. mucronata is usually either free 

 from, in the axil of, or from the very base of the leaf petiole. 



5. Marsilea tenuifolia Engelm. ex Kunze. Fig. 9. 



Plants slender, 5-17 cm. tall; petioles glabrous or essentially so; leaflets narrowly 

 cuneate, truncate and usually irregularly toothed at apex, more or less falcate, 

 villous with appressed hairs, to 25 mm. long, 2—8 mm. wide; sporocarps on short 

 slender peduncles, with divergent subequal teeth, 5-8 mm. long, 4—5 mm. in 

 diameter; sori 9 to 11 in each valve. M. vestita var. tenuifolia (Engelm.) Underw. 

 & Cook. 



On the edge of lakes, in shallow beds of creeks, and in periodically inundated 

 depressions, especially in old buff"alo wallows, in Tex. rare on the Edwards Pla- 

 teau, in Travis Co. in the Blackland Prairies and in the s. part of the Plains 

 Country; apparently confined to Tex. and Okla. (unverified). 



The narrowly cuneate leaflets with usually irregularly toothed apex are distinc- 

 tive of this species. 



6. Marsilea Fournieri C. Chr. Fig. 4. 



Plants small, usually about 8 cm. tall or less, villous throughout; rhizome stout 

 for the plant, compact and sometimes sending off short thick branches; petioles 



56 



