FLOWERING PLANTS AND FERNS OF ARIZONA 327 



Key to the species 



1. Achenes roughly transverse-ridged; petals not glossy, white, the claws some- 

 times yellow; plants aquatic or rarely palustrine, with finely dissected sub- 

 merged leaves: Subgenus Batrachium 1. R. aquatilis. 



1. Achenes not transverse-ridged; petals usually glossy; plants terrestrial or 

 palustrine, rarely aquatic, if so then with simple entire leaves (2). 

 2. Sepals persistent in fruit; fruits utricular; petals red; leaves compound, 

 dissected into Ungulate leaflets: Subgenus Crymodes- 2. R. juxiperixus. 

 2. Sepals not persistent when the fruit is mature; fruits not utricular; petals 

 yellow (3). 

 3. Wall of the fruit striate, the nerves 3 or more on each face, often branched; 

 ovary wall very thin and usually fragile; plant perennial, palustrine, 

 stoloniferous, with simple crenate leaves and elongate fruiting heads 

 each bearing 50 to 300 achenes: Subgenus Cyrtorhyncha. 



3. R. CYMBALARIA. 



3. Wall of the fruit not striate or nerved, thick and firm: Subgenus Euran- 

 unculus (4). 

 4. Styles lacking, the achenes practically beakless; plant annual, of brack- 

 ish marshes; juice very acrid; stem markedly fistulose; fruiting 

 head elongate, bearing 40 to 300 achenes: Section Hecatonia. 



4. R. SCELERATUS. 



4. Styles present, the achenes beaked (5). 



5. Leaves all entire or dentate, serrulate, or undulate; dorso ventral 



dimension of the achene not more than twice or thrice the lateral 



dimension: Section Flammula (6). 



6. Radical leaves lanceolate, oblanceolate, or linear, never ovate, the 



cauline leaves similar to the radical 5. R. flammula, 



6. Radical leaves ovate or cordate-ovate, the cauline leaves similar, or 



lanceolate or oblanceolate 6. R. hydrocharoides. 



5. Leaves all lobed, parted, or divided, except only the basal leaves of 

 R. globe rrimus (7). 



7. Nectary scale not forming a pocket, free laterally for at least two- 



thirds of its length; achene discoid, the dorsoventral dimension 



3 to 15 times the lateral dimension; sepals rarely with lavender 



or purple pigment: Section Chrysanthe (8). 



8. Petals 8 to 18; achene beaks 3 to 5 mm. long, straight or at least 



not regularly curved; plants perennial with stout stems up to 



0.9 m. long; leaves simple or compound, 3.5 to 15 cm. long, 



4 to 10 cm. wide 7. R. macraxthus. 



8. Petals 5; achene beaks 1 to 2 mm. long, curving above (9). 

 9. Sepals equaling or a little shorter than the petals, the latter 

 3 to 7 mm. long; head of achenes ovoid, 7 to 9 mm. long; 

 plant perennial; stems rooting at the nodes in Arizona 



specimens 8. R. macouxii. 



9. Sepals about twice as long as the petals, the latter 2 to 3 mm. 

 long; plant annual; stems never rooting adventitiously, 



erect 9. R. pennsylvanicus. 



7. Nectary scale forming a pocket, attached to the petal laterally for 

 all or most of its length; achene not discoid, plump, the dorso- 

 ventral dimension only 1 to 2.5 times the lateral dimension; 

 sepals alwavs tinged dorsallv with lavender or purple: Section 

 E pi rotes (10). 

 10. Fruiting receptacle and head of achenes globose or spherical; 

 achenes {each with a broad, thin stipelike base; basal leaves 

 entire or nearly so, the cauline leaves parted. 



10. R. GLABERBIMUS. 



10. Fruiting receptacle and head of achenes cylindric or ovoid; 

 achenes stipitate or winged at base; none of the leaves 

 entire (11). 

 11. Nectary scale not ciliate, glabrous, as is the whole petal (12). 



12. Achenes obovate 11. R. inamoenus. 



12. Achenes almost oblong __ 12. R. eschscholtzii. 



11. Nectary scale ciliate (except rarely in R. arizonicus) , the ad- 

 jacent petal surface sometimes bearing similar hairs ^13). 



