11(10). Petals 1-3 mm. long; mature achenes papillate, the papillae produced 

 into slender hooked spines or hooked hairs; nectary scale free 

 laterally 10. R. parviflorus. 



11. Petals at least 4 mm. long; mature achene either papillate or with straight 



or curved but not hooked stout spines, when papillate the papillae 

 not produced into hairs or spines, rarely smooth (12) 



12(11). Mature achenes papillate or rarely some or perhaps all of them smooth.... 

 1 1. R. Sardous. 



12. Mature achenes with stout spines on the margin or faces 12. R. muricatus. 



13(10). Style and achene beak practically lacking, if otherwise the achene with 

 a corky thickening on the margin of the body; nectary scale either 

 with the gland in a pocket on its ventral surface or else the scale 

 forked and prolonged anteriorly on the surface of the petal or 

 surrounding the gland (14) 



13. Style and achene beak present, the achene neither corky-keeled nor with 



nectary thickening on the margin of the body; nectary scale ventral 

 to the nectary (covering it), apically truncate or rounded (16) 



14(13). Styles and achene beaks practically lacking, the stigmas nearly sessile; 

 achene with some corky thickening of the pericarp.. 24. R. sceleratus. 



14. Styles and achene beaks well-developed, the beaks at least half as long as the 



achene bodies, 0.6-1.5 mm. long; achenes with conspicuous corky 

 thickening of either the keel or the pericarp beside the keel (15) 



15(14). Achenes each with corky thickening beside the inconspicuous keel (espe- 

 cially in the basal and ventral regions); leaves once- or twice-parted 

 or -lobed, pentagonal, 1-2 cm. long, 1.5-2.5 cm. wide, rarely dis- 

 sected but not triternately so; anthers elliptic, 0.5-1 mm. long; 

 petals 4-7 mm. long 25. R. Gmelinii. 



15. Achenes each with a conspicuous corky keel; leaves of aquatic specimens 



finely triternately dissected into ribbonlike segments 1-2 mm. wide, 

 the complete blades 1.5-10 cm. long and 2-12 cm. wide; anthers 

 oblong, 1-1.5 mm. long; petals 7-15 mm. long 26. R. flabetlaris. 



16(13). Nectary scale free laterally for at least two-thirds its length, not forming 

 a pocket (except in R. recurvatus var. recurvatus): dorsoventral 

 measurement of the achene 3 to 15 times the lateral; receptacle in 

 fruit (in most species) 1 to 3 times its length in anthesis; sepals 

 usually not lavender- or purple-tinged but sometimes markedly 

 so (17) 



16. Nectary scale attached to the petal laterally and forming a pocket; dorso- 



ventral measurement of the achene 1 to 2.5 times the lateral; 

 receptacle in fruit (in most species) 3 to 15 times its length in 

 anthesis; sepals usually tinged dorsally with purple or lavendar (25) 



17(16). Achene beaks regularly recurved or curved, or clearly falcate or hooked 

 at the apices, 2 mm. long or less, usually shorter than the bodies 

 or sometimes equaling them (the beak sometimes straight in R. 

 Macounii but then only about half as long as the body) (18) 



17. Achene beaks not regularly curved nor recurved, nor markedly hooked, 1.5 



or usually 2-4 mm. long, usually always equaling or exceeding the 

 bodies (23) 



18(17). Receptacle in fruit at least 3 times its length in anthesis, hispid; head of 

 achenes ovoid to cylindroid (19) 



18. Receptacle in fruit not more than 2.5 times its length in anthesis; head of 



the achenes hemispheroidal or globose (20) 



930 



