FLOWERING PLANTS AND FERNS OF ARIZONA 387 



11. Ribes quercetorum Greene, Calif. Acad. Sci. Bui. 1: 83. 1885. 



Grossularia quercetorum Cov. and Britt., North Amer. Fl. 22: 

 220. 1908. 



Superstition Mountains (Pinal County), Sierra Estrella (Mari- 

 copa County), 3,500 to 4,500 feet, steep rocky slopes and canyon 

 walls, growing in the Sierra Estrella with scrub oaks, Vauquelinia, 

 Penstemon microphallus, etc., November to March. South-central 

 Arizona, California, and Baja California. 



A shrub barely 1 m. high, tending to form low thickets. The 

 Arizona specimens approach E. leptanthum in length of the hypan- 

 thium but have the yellow flowers of R. quercetorum. 



51. PLATANAGEAE. Planetree family 



1. PLATANUS. Sycamore, buttoxwood, plaxetree 



Trees, with the outer bark flaking off and exposing the smooth, 

 whitish inner bark; buds enclosed in the dilated bases of the petioles; 

 leaves large, alternate, with palmately lobed blades; flowers monoe- 

 cious, very many in dense globular heads; sepals and petals minute; 

 pistils 3 or 4, separate; fruit a 4-sided achene, with a basal tuft of 

 long hairs. 



1. Platanus wrightii S. Wats., Amer. Acad. Arts and Sci. Proc. 10: 

 349. 1875. 



Southern parts of Coconino and Mohave Counties to Greenlee, 

 Cochise, Santa Cruz, and Pima Counties, 2,000 to 6,000 feet, along 

 streams, April to May. The Mogollon Escarpment coincides approx- 

 imately with the northern limit of this species in Arizona. New 

 Mexico, Arizona, and northern Mexico. 



Arizona sycamore. A large, spreading tree, attaining a height of 

 24 m. (80 feet), with beautifully arched, white-barked branches. 

 The roots effectively bind the soil, preventing excessive erosion. This 

 tree is perhaps not specifically distinct from the California sycamore 

 (P. racemosa Nutt). 57 



52. CROSSOSOMATACEAE. Crossosoma family 



1. CROSSOSOMA 



Rough-barked shrubs; leaves alternate, narrow, entire, thickish, 

 smooth and somewhat glaucous; flowers solitary, rather large; sepals 

 5; petals 5, white; stamens numerous, borne on a disk in the turbinate 

 hypanthium; pistils 2 to 5, becoming separate, several-seeded follicles, 

 these with thickish, reticulate-veined walls. 



Key to the species 



1. Follicles seldom less than 9 mm. long, oblong, ovoid, or somewhat obovoid, 

 usually conspicuously beaked 1. C. bigelovii. 



1. Follicles about 6 nun. long, broadly ovoid, abruptly short-beaked. 



2. C. PAKVIFLOHl'M. 



-" Wolf, Carl B. California plant notes. Occasional papers Rancho Santa Ana Hot. Card. 1: 31-43. 

 1935. (See p. 34.) 



