20b.1. Atriplex Linnaeus (subg. Obione) sect. Pleianthae S. L. Welsh, Rhodora. 102: 418. 2001.
Atriplex subg. Proatriplex W. A. Weber; Proatriplex (W. A. Weber) Stutz & G. L. Chu
Plants annual, monoecious. Leaves with normal (non-Kranz) anatomy. Staminate flowers with calyx lobes not crested. Pistillate flowers 2-5, typically with a 5-lobed perianth. Bracteoles triangular-ovate, united to middle or beyond, faces lacking tubercles. Seeds: radicle lateral, declined (the tip at opposite end from styles).
Species 1: w United States.
The similarity of the single taxon in this section, Atriplex pleiantha, with other species of Atriplex in the Colorado Plateau is illusory. Great weight has been given to the presence of apparently primitive inflorescences within the flowering bracteoles, but that feature is probably derived, not primitive. The linear, pale perianth segments subtending the 3-5 flowers are not unlike those in A. phyllostegia and A. suckleyi, both of which also lack Kranz anatomy in their leaves. Rather than representing primitive features, the presence of the perianth and, in the case of A. pleiantha, multiple flowers, these striking and seductively attractive features appear to represent independently derived occurrences within the highly variable genus Atriplex. If any of the taxa with included perianth are to be segregated within separate genera, then each should be so treated. However, such an approach might overshadow the true relationships to other species within the vast and complex genus. The radicle placement in seeds of sect. Pleianthae is inferior (lateral, with the tip of the radicle at a point diametrically opposed to the styles), possibly indicating a relationship divergent from the other species with perianth scales subtending the ovary in pistillate flowers. Because of the radicle position, the section is possibly best placed within subg. Atriplex. However, the radicle position might also be a derived condition in Atriplex in the broad sense, at least in some cases. If so, the relationship could well lie with other members now treated within the subg. Obione, the current but tentative placement of the section herein.
Stutz, H. C., G. Chu, and S. C. Sanderson. 1990. Evolutionary studies of Atriplex: Phylogenetic relationships of Atriplex pleiantha. Amer. J. Bot. 77: 364-369.