A. CANESCENS. 345 



7. A. GARRETTi Rydbcrg, Bull. Torr. Club 39: 312, 1912. — A. canescens garrelli. 



8. A. i.iNEAUis Watson, Proc. Am. Acad. 24: 72, 1889. — A. canescens linearis. 



9. A. MACKOi-ODA Ro.so Eiid Staiulloy, N. Am. Fl. 21: 72, 1916. — A. canescens maaropoda. 



10. A. oroiDKNTAi.LS Diotricli, Syn. I'l. 5: 537, 1852. — The same as Pterochiton occidenlaie, which see. 



11. A. ODONTOPTKRA Rydborg, I5ull. Torr. Club 31:404, 1904. — A form in which the thick wings of the 

 fruiting bracts are irregularly laciniatc-dentate. Perhap.s best referred to A. aptera (A. canescens aptera of 

 this treatment), as proposed by Rydberg (Fl. Rocky Mts. 249, 1917). Variation in the wings is noted under 

 No. 5 of this list. 



12. A. TETUAPTERA Rydborg, Bull. Torr. Club 39: 311, 1912. — ^Based upon Ohione tetmptera, which see. 



13. Calmgonum canescen.s Pursh, Fl. Am. Sept. 370, 1814. — The original description of .4. canescens typica. 



14. Obione berlandieri Moquin, in DeCandolle, Prodr. 13^: 114, 1849. — Based upon Atriplex berlandieri, 

 which see. 



15. O. canescens Moquin, Chcnop. Enum. 74, 1840. — The same as Calligonum canescens. 



16. O. occiDENTAUs Moquin, in DeCandolle, Prodr. 13': 112, 1849. — Based upon Pterochiton occidentale, 

 which see. 



17. 0. occiDENTALis var. ANGUSTiFOLiA Torrey, Bot. Mex. Bound. 184, 1859. — Leaves narrowly hnear 

 or lanceolate-linear, otherwise as in i4. canescens typica. Perhaps referable to subspecies linearis. The types 

 came from the Valley of the Rio Grande. 



18. O. TETUAPTERA Bcntham, Bot. Voy. Sulph. 48, 1844. — A form of A. canescens, differing from the type 

 form "in its narrow, linear leaves, only 2 to 5 mm. wide, in its more strongly reticulate fruit wings, which 

 have a broad sinus at the apex, and in that the free portion of the bracts is le.ss than half as long as the width 

 of the wing" (Rydberg, Bull. Torr. Club. 39: 311, 1912). It is now known that no one of these characters 

 is sufficiently constant, nor do any two of them vary in unison to such an e.\tent as to render of any value 

 the recognition of tetraptera as a species or as a subspecies. The type came from the coast of California and 

 probably from San Diego, where plants answering the description can now be found (c. g., Hall 11216, UC), 

 but plants with the same combination of characters grow as far inland as Utah (cf. Rydberg, Rocky Mt. Fl., 

 249, 1917). Bentham made no reference to the earlier Calligonum canescens in connection with his description. 



19. Pterochiton canescens Nuttall, Jour. Acad. Phila. II, 1: 184, 1847.— The same as A. canescens. 



20. P. OCCIDENTALE Torrcy and Fremont, in Fremont, Rep. Rocky Mts. Ore. Calif. 318, 1845. — The form 

 of A. canescens typica in which the leaves are linear-oblanceolate and the strongly veined wings of the fruit- 

 ing bracts 4 to 6 mm. or more wide, the margins only sinuate or d(!ntate. Described without reference to 

 Calligonum canescens, the original name for the species, which apparently was overlooked. 



RELATIONSHIPS. 



Although one of the most widely distributed of American Atriplexes, this species exhib- 

 its almost no tendency to intergrade with any other. Its most distinctive feature is the 

 development of dorsal as well as lateral wings from the fruiting bracts so that the whole 

 body comes to be 4-winged. In subspecies aptera there is sometimes a decided reduction 

 in these wings, and they are even wanting in a few bracts of this form. Since aptera has 

 also the merely subshrubby habit and the broad leaves of A. nuttalli, it may be that it 

 represents an intermediate stage in the evolution of canescens, but it is also possible that 

 it is a hybrid, notwithstanding its apparently fertile seeds. The infrequent occurrence 

 and the widely separated localities where it has been gathered, all within the general range 

 of the supposed parents, suggest a hybrid origin. A series of bracts from the type of 

 aptera are shown in plate 58. Some of these are not very unlike bracts frequently 

 found in A. nuttalli (cf. plate 51 and fig. 46, p. 32G). Whatever the origin of subspecies 

 aptera may be, the evidence as far as available points toward A . nuttalli as the nearest 

 relative of A. canescens. 



The five subspecies here accepted fall into two natural groups. One of these includes 

 typica, which is by far the most common and widely distributed of all, aptera, already 

 discussed, and garretti. This last is too little known to permit of definite placing in the 

 phylogenetic scheme. Its exceptionally broad and veiny leaves are unlike anything 

 known in genuine canescens, although the bracts are exactly as in the common typical 

 form. The leaf characters suggest a connection with A. obovata, but there is no evidence 

 that these two intergrade or hybridize. Further field studies and collections are much 

 needed in the southern part of the Great Basin, whence this form comes. 



