244 



[Vol. 9 



AJtDEN 



"T" aureum (Eastwood) Rydb. wherever they may be placed 

 eventually. The limits of "Thelypodiopsis" are not yet deter- 



mined. 



< MOOORAPHICAL DISTRIBUTION 



The genus Thelypodium as limited in the present paper has a 

 comparatively restricted distribution. The species are mostly 

 confined to the region between the Cascade or Sierra Nevada 

 Mountains of extreme western North America and the Rocky 

 Mountains of Montana, Wyoming, and Colorado. No species 

 are known from Canada or from Mexico. One doubtful plant, 

 T. vcrnale, occurs in New Mexico. Thelypodium stenopetalum 

 is found in the San Bernardino Mountains of southern Cali- 

 fornia: the most southern point known for the genus. Two spe- 

 cies with their varieties are found in the Rocky Mountains and 

 have crossed the Continental Divide in several places. Thely- 

 podium lilacinum readies western Nebraska and this marks the 

 easternmost known extension of Thelypodium. The genus is 

 richest in species in eastern Oregon. 



Thelypodium may be supposed to have originated in or not 

 far from the eastern Oregon region. Several reasons may be ad- 

 vanced to support this conclusion: (1) The greatest specific 

 concentration occurs in this region. (2) Those soecies held nre- 



viously to be the most primitive occur here. ('A) Conversely, 

 those species farthest from this region show in general those 

 characters considered to be of most recent development. (4) In 

 this region also occurs a genus with more primitive characters 

 than Thelypodium from which Thelypodium may have arisen. 

 This genus is Slanh ya. (5) From here is known that species 

 of Stanleya which is annual, has amplexicaul stem-leaves, and 

 no differentiated basal rosette — characters common in Thely- 



Uanlcya. Thi<; species is Stanleya conierti- 



ium 



flora (Robinson) Howell. 



In general the members of Thelypodium prefer a rather 

 strongly saline soil that at one season of the year at least is wet. 

 Consequently they are usually found on bottom lands rather 

 than on rocky hillsides. No species have become adapted to an 

 alpine habitat. 



'Species of this group ;hi<1 related forms have been recently treated as species of 



Sisymbrium by the author in Univ. Wyo. Publ. Bot. 1: 1-27. 1022. 



