FLOWERING PLANTS AND FERNS OF ARIZONA 351 



1. Microsisymbrium lasiophyllum (Hook, and Am.) O. E. Schulz, 

 Pflanzenreich IV. 105: 162. 1924. 



Turritis lasiophylla Hook, and Am., Bot. Beechev Vov. 321. 



1840. 

 Caulanthus lasiophyUus Payson, Mo. Bot. Gard. Ann. 9: 303. 



1922. 



Mohave, Maricopa, Pinal, Pima, and Yuma Counties, 3,500 feet or 

 lower, common in the western and southern deserts, usually among 

 bushes. February to April. Washington to Arizona, California, and 

 Baja California. 



Payson referred all of the Arizona specimens examined by him to 

 C. lasiophyUus var. utahensis (Rydb.) Payson. 



15. DIPLOTAXIS 



Plants annual or perennial, glabrous or sparsely hispid; leaves 

 coarsely toothed or pinnatifid; flowers rather few, in open racemes; 

 petals yellow; pods erect or ascending, long and narrow, somewhat 

 flattened; seeds in 2 rows. 



Key to the species 



1. Plant annual or biennial; stems scapose or subscapose; leaf blades coarsely 

 toothed, or pinnatifid with broadly oblong or triangular lobes; petals 

 about 6 mm. long; pedicels in fruit up to 22 mm. long__ 1. D. .mtralis. 



1. Plant perennial; stems leafy nearly to the inflorescence; leaf blades usually 

 deeply pinnatifid with elongate, linear or narrowly oblong lobes; petals 

 usually more than 6 mm. long; pedicels in fruit up to 40 mm. long. 



2. D. TEXUIFOLIA. 



1. Diplotaxis muralis (L.) DC, Regni Veg. Syst. 2: 634. 1821. 



Sisymbrium murale L., Sp. PL 658. 1753. 



Tuba, Coconino County, "common about buildings" (Clute 111), 

 Tucson, Pima County, " streets, spreading rapidly" (Thornber 7545 

 in 1913). In waste ground here and there in the United States; 

 introduced from Europe. 



2. Diplotaxis tenuifolia (L.) DC, Regni Veg. Syst. 2: 632. 1821. 



Sisymbrium tenuifolium L., Centuria PI. 1: 18. 1755. 



Benson, Cochise County, "common in railway yard and spreading" 

 (Thornber 5365); introduced from Europe. 



16. BRASSICA 



Plants annual or biennial, glabrous and glaucous, or sparsely and 

 stiffly pubescent; leaves petioled, or sessile and clasping, the blades 

 (at least of the lower leaves) lyrate-pinnatifid; flowers rather large, 

 in elongate racemes, the petals yellow; pods conspicuously beaked, 

 commonly torulose, dehiscent below, the beak indehiscent ; seeds in 

 one row. 



This genus includes the cultivated cabbage, cauliflower, turnip, 

 and mustard, as well as the weedy species enumerated here. Oil of 

 mustard, used medicinally as a skin stimulant (rubefacient), is ob- 



l>r,744°— 42 23 



