302 



GENUS ATRIPLEX. 



5. A. THORNBERi Standley, N. Am. Fl. 21 :57, 1916. — Based upon A. elegans thornheri, which see. 



6. Obione elegans Moquin, in De Candolle, Prodr. 13^:113, 1849. — A. elegans typica. 



7. 0. ELEGANS var.? radiata Torrey, Bot. Mex. Bound. Surv. 183, 1859. — The Thurber plant mentioned 

 with the description has not been seen, but Wright 571, from western Texas, is A. elegans typica with rather 

 deep incisions in the margins of the fruiting bracts. The original radiata of Torrey also included plants refer- 

 able to A. xvrighti, according to Coulter (Contr. U. S. Nat. Herb. 2:368, 1894). 



8. 0. radiata Torrey, 1. c. — Not distinguishable from A. elegans typica. Type locality, alluvions of the 

 GUa River, northern Sonora. 



Via. 42. — Fruiting bracts of Alriplex elegam: a, b, c, f, g, subspecies typica; d, e, subspecies fascieulata; a, from Durango 

 (110218 UC); b, from Tucson, Arizona (128540 UC); c, from Tucson, Arizona (7167 UC); d, from the Colorado 

 Desert, California (110328 UC); e, from the Mojave Desert, California (type of fasciculata, Gr); /, g, from a 

 single plant from Phoenix, Arizona (424737 US). All X 6. 



RELATIONSHIPS. 



The development of this species from the aggregate known as A. pentandra is quite 

 certain. It appears to be a derivative of some form near to the primitive subspecies 

 muricata which has become modified, especially in its bracts. These have been strongly 

 compressed and the marginal dentations regularly spaced, while the staminate terminal 

 spikes have been almost entirely suppressed, the flowers being confined in elegans to the 

 leaf-axils. From this point of view, the present species is a northwestern derivative, 

 which theory gains support from the close similarity between specimens of muricata from 

 the northern borders of its area and some of elegans from adjacent territory (e. g., Palmer 

 290, representing the former, and Palmer 1^97, representing the latter, both from near 

 Durango). Such plants are almost identical, except in the features mentioned. Fur- 

 thermore, the differences become more pronounced at greater distances from the ances- 

 tral home in Mexico. Thus, the bract appendages, so peculiarly developed in muricata, 

 are still present in a form of elegans known as variety thornheri (minor variation 2), 

 which is most plentiful in northern Sonora and southern Arizona, while the bracts 

 are always smooth in subspecies /asacwZato, a form of the Californian deserts. Thus the 

 connections with pentandra through its subspecies muricata (or possibly the little-known 

 minor variation cyclostegia) may be traced along a line that is also the route over which 

 the forms have passed in their northwestward migrations. 



Although this species has given rise to no others, and is therefore represented as at 

 the end of a line on the phylogenetic chart, it is by no means stationary. This is evi- 

 denced by several forms within the species, the best-marked of these being subspecies 

 fasciculata, in which there is a notable reduction in the width and dentation of the margins 

 of the fruiting bracts. The leaves and also the whole plant are often but not always 

 much reduced in size. The leaves are always entire, as far as known, which has led to 

 the use of this difference as a prime character for specific segregation. But it is quite 

 untrustworthy, for not only are a portion of the leaves entire in typical elegans, but in 

 some specimens with typical bracts apparently all the leaves are entire (Tucson, Ari- 

 zona, August 12, 1901, Thornber 7164, UC). The bract character is therefore taken as 

 the more reUable and the one which can best be correlated with features of habit and 

 distribution. That it is not of specific value may be seen from an examination of the 

 accompanying plate and text-figures, where it will be noted that all gradations may easily 

 be found. 



