Arizona siltbush

Zuckia arizonica Standley, J. Wash. Acad. Sci. 5: 58. 1915

Leaves 1.5-10 mm or more wide. Fruiting bracteoles without or with (1-)2(-4) prominent and (1-)4(-5) smaller vertical wings or ridges; achenes horizontal.

Flowering summer. Fine-textured or sandy, often saline and seleniferous substrates; ca. 1600 m; Ariz., Utah.

Despite the distinctive fruiting bracteoles and horizontal fruits of Zuckia brandegeei var. arizonica, which apparently represent a modification of the basic laterally flattened bracts of the brandegeei phase of the species, in a strict sense, the overall morphology of the plants is well within the range of vegetative variation existing within Zuckia brandegeei. Plants with staminate flowers have not previously been discerned from among the general collections of Z. brandegeei, and, indeed, immature or mainly staminate specimens of undetermined provenence are difficult if not impossible to identify from other phases of the species. Previous descriptions of Zuckia and its only species (Z. arizonica) are conspicuous in lacking discussion of staminate features. Supposed differences in vesture between the taxa apparently do not exist, and other diagnostic morphology is unknown. There are broad- and narrow-leaved phases within this variety also, about equivalent to those displayed by the varieties having vertical seeds. No additional taxonomic segregation appears to be possible, however.

Distribution of Zuckia brandegeei var. arizonica lies almost entirely within the range of the other two varieties. It is found on the Entrada, Summerville, Morrison, and Duchesne River formations; in eastern Utah; and on other siltstone and mudstone formations in north-central Arizona.