Proatriplex in Amer. J. Bot. 77: 366. 1990 sec. Zacharias & Baldwin 2010
Because it is more closely related to endemic North American genera of Atripliceae than to the worldwide Atriplex clade (see Fig. 1 ), Proatriplex is recognized here as a separate genus, as proposed by Stutz et al. (1990). Like its near relatives, Holmbergia and Stutzia, Proatriplex has pistillate flowers with perianths and non-Kranz anatomy; these three genera constitute a basal grade of taxa with pistillate perianths within a non-Kranz (C 3 ) clade. Proatriplex is the only genus in Atripliceae with the following combination of characteristics: perianths in both pistillate and staminate flowers; pairs of bracteoles connate less than half their lengths proximally and enclosing multiple pistillate flowers; and radicles pointing down.
Haploid and diploid counts are n = 9 ( Spellenberg 1986 ) and 2 n = 18 ( Stutz et al. 1990 ), respectively.
Annuals, erect, 0.5–1.7 dm high, monoecious. Stems branched from near the bases, succulent, glabrous, occasionally sparingly farinose; branches ascending, white-yellow or reddish, the branchlets with sparse inflated hairs distally. Leaves solitary, numerous, usually alternate, occasionally subopposite, the petioles 5–12 mm long; blades 5–285–28 mm, ovate to suborbiculate, succulent, the bases cuneate to truncate, the margins entire, the apices obtuse to acute to mucronate, the surfaces bright green, initially with unicellular inflated hairs; anatomy non-Kranz. Inflorescences with staminate and pistillate flowers mixed in the inflorescences, or with the staminate flowers glomerulate in interrupted, terminal spikes and pistillate flowers in leaf axils along stems. Staminate flowers ebracteolate; perianths 5-lobed, united in proximal 1/2, 1–1.5 mm long, the lobes cucullate at apices, not crested; stamens 5, each opposite a perianth lobe; filaments inserted on a disc, subulate; anthers exserted. Pistillate flowers 2–6 within paired bracteoles; perianths unchanging and persistent at the bases of the fruits, of 5 hyaline scales, the scales 1–1.5 mm, lanceolate or oblanceolate to ovate, the margins distally sparsely ciliate; stigmas 2, filiform, slightly exserted. Fruiting bracteoles accrescent, paired, enclosing 2–6 pistillate flowers, slightly connate in proximal 1/2, 3–7 3–7 mm, triangular-ovate to orbiculate, the bases sessile or stipitate (1–4 mm long), the margins entire, the apices obtuse, mucronate, or acute, the surfaces glabrous, lacking tubercles. Utricles not spongy, falling at maturity, 1.5–21.5– 2 mm, approximately equal in length to perianths, suborbicular to obovoid, laterally compressed; pericarps membranous, adherent to seeds; seeds vertical, smooth, black, shining; seed coats crustaceous; perisperm copious, farinaceous; embryos annular; radicles pointing down toward base.
Proatriplex is most common on desert badland landscapes, often growing by itself in saline, clay soils of isolated depressions, sometimes with other halophytes of the salt desert shrub community [e.g. Kochia americana S. Watson, Suaeda torreyana S. Watson, Atriplex obovata Moq., Monolepis nuttalliana (Schult.) Greene, and Distichlis spicata (L.) Greene ( Stutz et al. 1990 )]. Populations can range from sparse (10– 50 plants/m² ) to dense (50–80 plants/m² ) ( Stutz et al. 1990). Proatriplex is locally abundant when conditions are favorable.