FLOWERING PLANTS AND FERNS OF ARIZONA 175 



40. Carex rostrata Stokes in With., Bot. Arr. Veg. Brit. ed. 2, 2: 



1059. 1787. 

 Apache and Coconino Counties, also reported from Pima County, 

 about 7,500 feet. Greenland to Alaska, south to Delaware, Indiana, 

 New Mexico, Arizona, and California. 



10. PALMAE. Palm family 



1. WASHIXGTOXIA. Califorxia-palm 



Tree; leaves clustered at apex of the columnar trunk around the 

 terminal bud, the petioles long, stout, with hooked marginal spines, 

 the blades very large, splitting longitudinally into numerous narrow 

 segments, these fibrous-margined; inflorescences axillary, subtended 

 by spathes, many-flowered, drooping; flowers perfect or unisexual; 

 perianth segments 6, in 2 series. 



1. Washingtonia filifera Wendl. ex. S. Wats., Bot. Calif. 2: 211. 1880. 



Kofa Mountains, Yuma County, about 2,500 feet. Southwestern 

 Arizona, southeastern California, and northern Baja California. 



Although California-palms are extensively planted in the southern 

 part of the State, the approximately 100 individuals growing in small 

 lateral canyons or pockets in the walls of a larger canyon in the Kofa 

 Mountains are the only plants of this species known in the wild in 

 Arizona. The trees here reach a maximum height of about 30 feet 

 (9 m.) and the trunk soon becomes naked. The inflorescences, includ- 

 ing the peduncle, reach a length of 12 feet (3.6 m.). Some of the 

 botanists who have studied these palms believe that the Arizona form 

 is not identical with the California plant, but Bailey refers it to W. 

 filifera. 18 



11. ARACEAE. Arum family 



1. PISTIA. Waterlettuce 



Plant aquatic; stem very short; leaves in a rosette floating on the 

 water surface, the petioles short, the blades broadly obovate; inflores- 

 cence axillary, few-flowered, enclosed in a small white spathe; flowers 

 monoecious, the staminate ones above; perianth none; pistil solitary; 

 ovary 1 -celled. 



1. Pistia stratiotesL., Sp. PL 963. 1753. 



Yuma, in an irrigation canal (Sister Mary Xoel 44), perhaps adven- 

 tive. Southeastern United States and widely distributed in the Tropics. 



12. LEMNACEAE. Duckweed family 



Plants minute, floating on the surface of ponds and slow streams, 

 thalluslike, without differentiation of stem and leaf; flowers (rarely 

 produced) borne on the edges of the fronds in a minute 1 spathe, monoe- 

 cious; perianth none; stamen and pistil each solitary; fruit a utricle. 



Key to the genera 



1. Rootlets several; fronds prominently several-nerved 1. Spirodela. 



1. Rootlet solitary; fronds few-nerved, often very obscurely so 2. Lsmna. 



Species of the genus Wolffiella, characterized by the absence of rootlets and 

 spathes and by the elongate, very thin fronds, are to be looked for in Arizona. 



i- Bailey. L. It. washingtonia. Gentes Herbarium 4: 53-8L 1936. (Pp. 72, 73.) 



286744° 12—12 



