Norton — Plants of the Southtoestern United States. 37 



tributed species in the desert regions of the Southwest seems 

 to indicate that the isolation of mountain regions, affording 

 favorable growth for certain species by intervening deserts 

 where the same species cannot grow, offers a condition com- 

 parable with the differentiation of forms in insular floras. 

 This seems to me to be especially true with some mountain 

 species of Euphorbia, which I have examined, in which the 

 means of dissemination is limited, most of the isolated moun- 

 tains of Arizona and New Mexico having their peculiar vari- 

 ation not occurring elsewhere. 



Ctperus longispicatus n. sp. 



Perennial ; 1 to 2 m. high; leaves several dm. long, 1 to 2 

 cm. broad; peduncle naked, surmounted by an involucre of 

 several leaves, the larges as much as 1 m. long, 1 cm. or 

 more wide, prominently veined, rough margined ; umbel of 5 

 to 10 rays, some very short, others 15 cm. long, compound, 

 with 2 to 5 spikes 1 to 3 cm. long; spikelets slightly flattened, 

 2 to 4 cm. long, 20- to 40-flowered, spreading, falling away 

 from the axis and breaking up; scales concave or slightly 

 keeled toward the apex, imbricated, ovate, short pointed, 

 light yellowish-brown with a prominent green stripe on the 

 back and two distinct nerves between this and the broad 

 membranous margin, persistent on the swollen joints of the 

 rachis, the membranous margins of which almost inclose 

 the obpyramidal, 3-angled, light brown, pointed achenes ; 

 stamens 3 ; achenes 1 mm. long, the apex obtuse with a 

 mucron which bears the 3-cleft style. — Plate V. 



Type collected by B. F. Bush at San Antonio, Texas, 1900, 

 no. 1248. 



Common in water, conspicuous from its large size and the 

 great length of the spikelets. 



DiTHTREA WiSLiZENi Engelm. 



The range of this interesting crucif er is extended eastward 

 by specimens collected in western Oklahoma by Mark White, 

 in 1899. 



