298 



GENUS ATRIPLEX. 

 RELATIONSHIPS. 



This is believed to represent the plexus from which a large series of species has origi- 

 nated. At least 7 major species can be traced back with more or less certainty to this 

 stock. They are all western and seem to have had their connection through the sub- 

 species muricata of Mexico. Each has undergone essential modifications in one or more 

 of the pentandra characters, and in every case the change has been in the direction of sim- 

 plification or in the development of special features. These changes will be indicated 

 under the heading of Relationships as each of the derived species is reached. The list 

 includes: elegans, microcarpa, wrighti, bracteosa, linifolia, fruticulosa, and coulteri. It is 



Lvs. elliptic tx) lanceo- 

 late or linear; bracts 

 3-4mm. long (rarely 

 4.B). S.Atlantic and 

 Gulf coasts and West 

 Indies 



Bracts 2.5-jmm. long 

 (rarely 3.E), mostly crested 

 but sometimes smooth, 

 not strongly reticulated; 

 lvs. greener above ' 



Bracts about j mm long, 

 rvj crests, faintly reticu- 

 lated; Ivs. broadly ell'piic, 

 densely white-scurfy on 

 both sides, crisp- 

 West lnd.es 



Lvs. broadly elliptic to 

 ovate ; bracts A-6 mm. 

 long. N.Atlantic 

 'Coast 



Bracts 3-6 mm. long, 

 mostly crested, reticulated; 

 lvs greener above 



Fig. 41. — Phylogenetic chart of the subspecies of Atriplex penlandra. 



probable that A. barclayana should be added to the list. If this is done pentandra will 

 then stand near the base also of the large phylogenetic branch of dioecious shrubs, for 

 barclayana seems to be a lateral branch which sprang from the common stock of this 

 group. It is also possible that the present species is basal to the pusilla, truncata, and 

 argentea groups, but for a number of reasons, the most important of which is a modifica- 

 tion in the shape of the fruiting bracts combined with a rather well-developed separation 

 of the sexes, it is given a position in the chart (fig. 29, p. 238) superior to these. 



Evolution within the collective species A. pentandra has progressed to a high stage. 

 The result is a number of subspecies well separated in their extremes, yet held together 

 by a series of intergrading forms. Two principal branches are noted, an eastern and 

 a western. The former comprises two groups of forms assembled under the subspecific 



