348 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



7. Lepidium medium Greene, Erythea 3: 36. 1895. 



Lepidium virginicum L. var. medium C. L. Hitchc., Madrono 



3: 285'. 1936. 



Coconino County to Cochise and Pima Counties, 6,000 feet or lower, 

 February to August. Montana to British Columbia, south to Texas, 

 Arizona, and California. 



Resembles the common peppergrass of the eastern United States 

 (L. virginicum L.) but all Arizona specimens examined by the writers 

 have incumbent (not accumbent) cotyledons. Occurs in two forms 

 that are about equally common in Arizona, the typical form with 

 upper parts of the stem and pedicels glabrous, and var. pubescens 

 (Greene) Robinson (L. hirsutum Rydb.) with stems and pedicels 

 puberulent or cinereous-pilose throughout. 



8. Lepidium densiflorum Schrad., Index Sem. Hort. Goettingen 4. 



1832. 



Lepidium apetalum of Amer. authors. Not Willd. 



Apache, Coconino, and Yavapai Counties, 5,000 to 8,000 feet. 

 Widely distributed in the United States and Canada. 



The common form in Arizona is var. bourgeauanum (Thell.) C. L. 

 Hitchc., which differs from typical L. densiflorum in having distinctly 

 flattened pedicels and capsules about 3 mm. long. 



Lepidium perfoliatum L., a European species sparingly naturalized in southern 

 California, has been collected in the railway yard at Flagstaff, Coconino County 

 (Whiting 1697, in 1941). It has the lower leaves bipinnatifid into narrowly 

 linear divisions and the upper leaves entire, broad, rounded, and cordate-clasping. 



11. THLASPI 



Plants herbaceous, annual or perennial, glabrous; stem leaves auric- 

 ulate-clasping ; flowers small, the petals white or tinged with purple; 

 capsules 2-celled, dehiscent, flattened at a right angle to the partition; 

 seeds 2 or more in each cell. 



Key to the species 



1. Plant annual; stems commonly 30 cm. long or longer, usually branched; 

 capsules orbicular or nearly so, rounded or slightly cuneate at base, at least 

 10 mm. wide at maturity, broadly winged all around, deeply notched at 

 apex; style minute, much shorter than the notch 1. T. arvense. 



1. Plant perennial; stems not more (usually much less) than 30 cm. long, not 

 branched; capsules wedge-shaped, not more than 6 mm. wide, not winged 

 or obscurely so near the truncate or very shallowly notched apex; style 

 elongate, much longer than the notch ; sepals usually purplish. 



2. T. FENDLERI. 



1. Thlaspi arvense L., Sp. PI. 646. 1753. 



Keam Canyon, Navajo County, 6,300 feet (Peebles and Smith 

 13413). Penny cress. A troublesome weed in some parts of the United 

 States, naturalized from Europe. 



2. Thlaspi fendleri A. Gray, PL Wright. 2: 14. 1853. 



Thlaspi purpurascens Rydb., Torrey Bot. Club Bui. 28: 281. 

 1901. 



Apache County to Hualpai Mountain (Mohave County), south to 

 Cochise and Pima Counties, 5,000 to 12,000 feet, mostly in coniferous 



