286 



GENUS ATRIPLEX. 



in central and northern California (where the entire-leaved form is exceedingly common), and on the 

 other hand, it ranges to southern California, the best example of large, trinervate and dentate leaves coming 

 from southern Santa Barbara County. Furthermore, the bracts in the type specimen are united well above 

 the middle and most of them are short-stalked, so that these features can not be used for the separation of tri- 

 nervata. It seems, therefore, that Jepson was correct in reducing his species to expansa (Jepson, Fl. Calif. 437, 

 1914) and that it represents only a common response to conditions favorable for exceptional growth. Type 

 locality, near the Arequipa Hills, Solano County, California. 



11. A. voLUTANS Nelson, Bull. Torr. Club 25:203, 1898.— The more globoid robust form oi A . argentea typica, 

 as indicated by Nelson (Bot. Gaz. 34:358, 1902). Type locality, Seven-Mile Lake, Wyoming. 



12. Obione argentea Moquin, Chenop. Enum. 76, 1840. — A. argentea typica. 



0^ 



C 



37 



38 



FiQ. 37. — Minor variations of Atriplex argentea: a, b, c, from the type ol A. rydbergi (minor variation 9J; d, e, /, g, a form 



from Grand Junction, Colorado, intermediate to typical argentea. All X 0.8. 

 Fio. 38. — Atriplex argentea expansa, minor variation 10 (A. trinervata Jepson) :fa, leaf, X 1 ; fc, c, fruiting bracts, X 2. Drawn 



from the type specimen (Herb. Jepson). 



RELATIONSHIPS. 



This is looked upon as the central species of a large group that has progressed beyond 

 A. dioeca, A. phyllostegia, etc., in a number of characters, but especially in the complete 

 suppression of the perianth. Since each of the other species of the argentea group exhibit 

 certain specialized features, the relation between them and argentea will be discussed 

 as they are reached in the sequence. 



There are here included within the species a considerable number of forms, certain of 

 which represent diverging lines of development. However, all of the variations seem 

 to belong to two principal branches, or stocks. These are treated as subspecies, namely 

 typica and expansa. In the former, even the upper leaves usually exhibit at least a short 

 petiole, while in the latter the upper leaves are very closely sessile and the blades com- 

 monly incurved between the stems (plate 44, figs. 1, 6, 7). The two are not widely 

 separated geographically, but typica is chiefly a Mississippi Valley, Rocky Mountain, and 

 Great Basin form, while expansa belongs to the southern borders of the United States 

 and to California. They are therefore believed to be geographic types which are 

 separating in their morphologic characters, although an overlapping along the boundaries 

 has prevented a complete separation. The absence of a complete parallelism between 

 geographic distribution and established characters is evidenced by the occasional appear- 

 ance of plants of one subspecies well within the area assigned to the other. Examples 



