FLOWERING PLANTS AND FERNS OF ARIZONA 591 



2. Bracts at anthesis concealing the calyx tube, mostly broadly ovate, the 

 lower portion of different texture from the upper, scarious or thinly 

 membranous, whitish, the teeth usually more than 8 and shorter than 

 the width of the undivided central portion of the bract. 



1. M. IXVOLUCRATA. 



2. Bracts at anthesis not concealing the calyx tube, lanceolate, green and of 



uniform texture throughout, the teeth 6 to 8, at least as long as the 



width of the undivided central portion of the bract__ 2. M. tricuspis. 



1. Outer filaments not cleft at apex; petals yellow or orange, often fading whitish; 



flowers not bracteate or, if loosely so, then the bracts not deeply laciniate, 



often entire (3). 



3. Stems not conspicuously whitish, these and the capsules hispid with stout, 



glochidiate hairs 0.5 to 1.0 mm. long; leaf blades thin, deep green, irreg- 

 ularly dentate and often hastately lobed near the base; petals orange 

 yellow, 6 to 10 mm. long; capsules elongate, clavate or narrowlv ob- 

 conic: Section Eumentzelia (4). 

 4. Petioles of the lower leases more than half as long as the blade; blades 

 broadly ovate, less than twice as long as wide; filaments of the outer 

 stamens petaloid-dilated toward the apex 3. M. aspera. 



4. Petioles less than half as long as the blade; blades lanceolate to ovate, 



often much more than twice as long as wide; filaments not dilated. 



4. M. ASPERULA. 

 3. Stems becoming conspicuously whitish, scabrous-puberulent, short-pilose, 

 or glabrate; leaf blades thickish, light green or yellowish green, not 

 hastate; petals yellow (5). 



5. Capsules clavate or narrowly obconic, more than 5 times as long as wide; 



seeds pendulous, thick, faceted, not winged; hairs not glochidiate, 

 the longer ones very slender; plants annual; outer filaments not or 

 scarcely dilated; leaf blades mostly pinnatifid: Section Trachyphytum 

 or Acrolasia (6). 

 6. Seeds appearing smooth at low magnification, grooved on the angles. 



5. M. AFFINIS. 

 6. Seeds evidently muriculate at low magnification, not grooved or but 

 slightly so on one of the angles; blades of the leaves deeply pinna- 

 tifid, or the upper ones few-toothed or entire (7). 



7. Petals 8 mm. long or longer 6. M. nitens. 



7. Petals less than 8 mm. long 7. M. albicaulis. 



5. Capsules turbinate or broadly obconic, not more than 3 times as long as 



wide; seeds horizontal, thinly lenticular, winged; glochidiate hairs 



usually present, at least on the calyx; plants biennial or perennial; 



outer filaments more or less dilated: Section Bartonia or Nutiallia (8). 



8. Petals pale yellow when fresh, 15 to 20 mm. long; stems up to 1.5 m. 



long, stout, strict, not branched below; leaf blades sinuate-dentate, 



the lower ones up to 20 cm. long; capsules 20 to 30 mm. long, 



commonly about 3 times as long as wide, acutish at base. 



8. M. RUSBYI. 



8. Petals bright yellow when fresh (9) . 



9. Leaf blades all or mostly pinnatifid; stems usually tall, 50 cm. long 

 or longer; petals 10 to 20 mm. long; capsules i0 to 20 mm. long, 

 1.5 to 3 (commonly about 2) times as long as wide, acutish t<> 



rounded at base 9. M. pumila. 



9. Leaf blades sinuate-dentate or nearly entire; stems low, less than 



50 cm. long, usually branched from the base; capsules about 



10 mm. long, less than twice as long as wide, rounded at base (10). 



10. Stems herbaceous, slender, becoming smooth; leaf blades lanceolate 



or narrowly oblong; petals up to 15 mm. long__ 10. M. Integra 



10. Stems suffrutescent, stout, scabrous-pubescent; leaf blades ovate 



or oblong-ovate; petals not more than 10 mm. long. 



11. M. puberula. 



1. Mentzelia involucrata S. Wats., Amer. Acad. Arts and Sci. Proc. 20: 



367. 1885. 

 Western Maricopa, western Pinal, and Yuma Counties, 2.200 feet 

 or lower, dry sandy soil, March and April. Southwestern Arizona, 

 southeastern California, and northwestern Sonora. 



286744°— 42 38 



