30. Ranunculus subrigidus Drew. 



Glabrous or essentially glabrous aquatic perennial with filiform roots; stems 

 submersed, rooting at the lowest nodes, to about 6 dm. long, branching, with 

 large air chambers in the cortex; leaves cauline, all submersed and finely dis- 

 sected into filiform divisions, once- or twice-trichotomous then dichotomous, the 

 leaf as a whole globular, usually not fully collapsing when withdrawn from the 

 water (but sometimes so), usually circinate, 1-2 cm. long, 1.5-3 cm. broad, much 

 shorter than the adjacent internodes; petioles developed only occasionally, the 

 first leaf divisions arising within the stipular leaf base (the leaf base dilated and 

 the ends usually free); pedicels stout, 2-4 cm. long in flower, about 1 cm. longer 

 and markedly recurved at the bases in fruit, glabrous; sepals 5, light-green, spread- 

 ing, elliptic, 3-5 mm. long, deciduous before the corolla; petals 5, white or the 

 bases yellow, 5-9 mm. long, 2-4 mm. broad, narrowly obovate, the nectary scale 

 nearly or fully obsolete; stamens 5 to 10; achenes 30 to 80, in a globose-ovoid 

 head 4-6 mm. long and 4-5 mm. in diameter, obovoid, 1-1.5 mm. long, roughly 

 transversely-ridged, glabrous, hispidulous or glabrate, the style largely deciduous, 

 the achene beak 0.2-0.5 mm. long; receptacle subglobose, 1 mm. long in flower, 

 1-1.5 mm. long in fruit, hispidulous. R. circinatus Sibth. var. subrigidus (Drew) 

 L. Benson. 



In ponds, lakes or pools, often brackish, frequently attached and floating in 

 streams, in the Tex. Rio Grande Valley, N. M. (Rio Arriba, San Miguel and 

 Grant cos.) and Ariz. (Coconino and Gila cos.), May-Sept.; from Can. s. to cen. 

 Mex. 



31. Ranunculus longirostris Godr. White water-crowfoot. 



Similar to R. subrigidus; leaves firmer, often stiflf, the stipular base larger and 

 from three fourths to entirely adnate to the very short petiole; pedicels appearing 

 to be axillary (actually terminal, the stem sympodial), 1-5 cm. long, apparently 

 not recurved in fruit, glabrous; sepals yellowish-green or purplish, spreading, 

 narrowly elliptic, 3-4 mm. long, 1-1.5 mm. broad, early-deciduous; petals 5, 

 white, obovate, 4-9 mm. long, 2.5-6 mm. broad; the nectary scale reduced to a 

 very shallow pocket or a lunate ridge along the base and sides of the gland or 

 wholly absent, the glandular area only 0.2-0.3 mm. in diameter; stamens 10 to 

 20; achenes 7 to 25 in a subglobose cluster or head 3-5 mm. long and 4-6 mm. 

 in diameter, obovoid, 1.3-1.7 mm. long, roughly transversely-ridged, glabrous or 

 hispidulous, the margin evident, the slender beak 0.7-1.1 mm. long and straight; 

 receptacle globose or pyriform, 1 mm. long in flower, 1-2 mm. long in fruit, 

 densely hispid. 



Floating in water of streams and lakes, often forming large mats in Okla. 

 (McCurtain and Beaver cos.) and in Tex. from the Rio Grande Plains to the 

 Panhandle, N. M. (widespread) and Ariz. (Apache and Navajo cos.), Apr .-July; 

 from Can., s. to Ariz., N.M., Tex., Ark., Ala. and Del. 



10. Thalictnim L. Meadow-rue 



Plants herbaceous, perennial, often polygamous or dioecious; leaves alternate, 

 rather large, twice or thrice ternate with numerous usually cleft or shallowly 

 lobed leaflets, the basal leaves long-stalked; petioles dilated at base; flowers mostly 

 unisexual, small, greenish or yellowish, usually in terminal panicles; sepals 4 or 

 5, caducous, petaloid or greenish; petals none; stamens numerous, exserted, the 

 filaments filiform or slender-clavate; stigma unilateral; achenes 4 to 15, with 

 longitudinal grooves or ribs extending from base to apex, sometimes inflated. 



About 150 species, mostly in the Northern Hemisphere. 



957 



