Brandegee’s siltbush

Grayia brandegeei A. Gray, Proc. Amer. Acad. Arts 11: 101. 1876 (as brandegei); Atriplex brandegeei (A. Gray) Collotzi ex W. A. Weber

Shrubs, branching from persistent woody base 0.5-2 dm; stems 1-5 dm. Leaves 13-80 × 15-42 mm. Staminate flowers with perianth cleft to middle or below, 1.5-1.8 mm. Pistillate flowers few, intermixed in otherwise staminate spikes; bracteoles laterally or vertically compressed, with vertical or horizontal achenes respectively, when mature either laterally flattened, 2(-4)-winged, 3.4-9 mm diam., or dorsiventrally compressed and not or 1-4(-5)-ribbed and 2-winged, (1.8-)2-2.5 mm diam. Achenes included within bracts, 1.2-2.2 × 1.2-2.2 mm.

Varieties 3 (3 in the flora): w United States.

When he described Grayia brandegeei A. Gray (1876b) noted, "While pleased with an accession to this genus, and with the opportunity of associating it with the name of an excellent correspondent who discovered it, I must add that it does not much strengthen the genus." Grayia, within which the species has long resided, shorn of G. brandegeei, consists of G. spinosa (Hooker) Moquin-Tandon. Grayia brandegeei was clearly regarded, even by its author, as not closely allied to G. spinosa, the type species of Grayia, even though they shared features of bracteole compression, seed position, and rounded axillary buds. The two species otherwise differ markedly in stature, vestiture, and in the nature of the bracts. In G. spinosa the bracteoles are thickened marginally and filled internally with a spongy cellular matrix. Those of G. brandegeei are thin margined and lack a spongy cellular matrix. Leaf shape, plant stature, and ecological associates also differ. Grayia spinosa is a plant mainly of low-salinity substrates, and is rather widely distributed over the West from Washington to Montana and south to California, Arizona, and New Mexico (S. L. Welsh et al. 1993).

Besides the similarity of stature, staminate inflorescences, and flowers, the plants herein considered within Zuckia occupy similar, relatively high-saline, gypsiferous, and seleniferous substrates. The major difference between the lone taxon, Z. arizonica, on which the genus initially rested, and G. brandegeei sensu lato, is to be found in the fruiting bracteoles, which in Z. arizonica are mainly four-ridged and narrowly two-winged, and accommodate the mostly horizontal arrangement of the achenes.

Inclusion of Grayia brandegeei, with its laterally flattened (rarely three- or four-winged) fruiting bracteoles and vertical achenes, within Zuckia, with its architecturally differing bracteoles, requires explanation. At first glance, the six-ribbed bracteoles around a horizontal achene appear to be both distinctive and diagnostic. The bracteoles, however, merely accommodate the shape of the achene, and what is apparently very distinctive is only a structural modification. Examination of the fruiting bracteoles of all taxa previously included within Grayia brandegeei demonstrates existence of a rather wide array of bracteole morphology. Bracteoles are typically laterally compressed and samaralike. However, even on the same individual plant, there occur three-winged bracteoles, and in some bracteoles there are evident veins on one or both surfaces. The veins appear in the same position as the lateral ribs on the transversely flattened bracteoles of the arizonica phase of the species. There is also considerable variation in the morphology of the transversely flattened bracteoles, ranging from merely oval with a hint of the wings, the lateral ribs lacking altogether, to very definitely winged and with two or more lateral ribs. The overall similarity of the plants, their growth habit, and their preference for fine-textured, saline, often seleniferous substrates rather narrowly confined within the Colorado Plateau indicates a rather close relationship best reflected in their alliance.

In spite of the similarity of substrate inhabited by the three taxa, their geographic ranges are mainly discrete. This is due at least partially to the autecological differences in the habitats they occupy, and to actual geographical separation, even though apparently sympatric when mapped.