BUCKWHEAT FAMILY 229 



solitary, 1-3-flowered, tubular, 5-6-dentate, with 3-6 spinulose-tipped spurs 

 below. Perianth 6-lobed. Stamens 9, inserted near the base of the perianth. 



1. C. Thurberi A. Gray. Diffusely branched annual, 5-15 cm. high; leaves 

 spatulate, glabrous, 1-2 cm. long; involucre 1-2-flowered, chartaceous, venose, 

 5-toothed at the apex; spurs 3, large, divergent, conic, as well as the teeth short- 

 cuspidate; segments of the perianth linear-spatulate, hirsute towards the base. 

 Arid regions: Ariz. s Utah Calif. L. Son. My-Je. 



4. CHORIZANTHE R. Br. 



Low annual or perennial herbs, with sessile cymosely arranged involucres 

 and opposite or verticillate leaves, or the lower leaves sometimes alternate. In- 

 volucres 1-flowered, gamophyllous, with angular or costate tube and 2-6 cuspi- 

 date or aristate teeth or lobes. Perianth corolla-like, 6-lobed or 6-parted. Sta- 

 mens 9, rarely 6 or 3. Achenes 3-angled. 



Involucre not strongly sulcate, 5-toothed; filaments adnate to the perianth nearly up to 

 the base of the lobes. 1. C. Watsoni. 



Involucres strongly sulcate, 6-toothed; filaments adnate only to the lower part of the 



perianth-tube. 



Leaves linear-oblanceolate to linear. 2. C. brevicornu. 



Lower leaves broadly spatulate. 3. C. spathulata. 



1. C. Watsoni A. Gray. Low branched annual, appressed-canescent; 

 stem 2-5 cm. high; leaves linear or linear-spatulate, canescent; involucres cy- 

 lindric, 5-6 mm. long; teeth 5, unequal, acerose-subulate, recurved; perianth 

 with a cylindric tube; stamens 9; embryo straight; cotyledons linear. Desert 

 regions: Wash. 'Ida. 'Nev. Calif. Son. My-Jl. 



2. C. brevicornu Torr. Branched annual; stem 5-20 cm. high, strigose; 

 lower leaves narrowly linear-oblanceolate, 2-7 cm. long, strigose; bracts small, 

 with a hooked mucro; involucres narrowly prismatic, about 5 mm. long; lobes 

 subequal, subulate-arista te, recurved; perianth 1.5 mm. long, 5-lobed; lobes 

 ovate, entire; stamens 3. Desert regions: Ariz. -s Utah Nev. -se Calif. L. 

 Son. Ap-My. 



3. C. spathulata Small. A branched annual; stem strigose-canescent, 

 5-20 cm. high; lower leaves 1.5-3 cm. long, spatulate, hirsute-strigose on both 

 sides; involucre prismatic, 5 mm. long, strigose; lobes 6, subulate, recurved, 

 spinulose-tipped, the alternating narrower; perianth 2 mm. long; lobes ovate; 

 stamens mostly 3. Desert regions: Ida. Nev. Son. My-Je. 



5. ACANTHOGONUM Torr. 



Dwarf annuals, with obovate leaves. Bracts spinescent-subulate. Invo- 

 lucres axillary, sessile, subtended by a 3-fid bractlet, 1-flowered, 3-cleft to near 

 the base; tube short, 3-angled; segments unequal, lanceolate, tapering into a 

 subulate pungent tip. Flowers hermaphrodite, sessile; perianth equally 6- 

 toothed, closed in fruit. Stamens 6-9, adnate to the whole tube of the perianth. 

 Styles 3, short; stigmas capitate. Achenes ovate, 3-angled. 



1. A. rigidum Torr. Plant at first lanate; stem 1-3 cm. high; leaves long- 

 petioled, white-tomentose beneath; involucres with elongated aristiform or 

 subulate spinescent bracts; perianth with a cylindric tube and obtuse base; 

 stamens 9. Chorizanthe rigida (Torr.) A. Gray. Desert regions: N.M. -s Utah 

 Nev. s Calif.; n Mex. L. Son. Ap-My. 



6. PTEROSTEGIA F. & M. 



Slender annuals, diffusely branched, dichotomous, with opposite leaves and 

 foliaceous bracts. Involucres axillary, sessile, consisting of a single 2-lobed 

 bract, enlarged in fruit, scarious and reticulate, loosely enclosing the achene, 

 2-gibbous on the back. Perianth 6-parted, or rarely 5-parted. Stamens 3 or 

 6. Achenes triangular, glabrous. 



1. P. drymarioides F. & M. Stem 1-3 dm. long; lower leaves long-peti- 

 oled, flabelliform, obcordately 2-lobed or emarginate, those of the upper branches 

 rounded-obovate or spatulate; fruiting involucre 2-3 mm. long, deeply 2-lobed, 



