Flora of North America species comparison

erect, rarely ascending, branched above base (occasionally with slender branches near base);

branches straight or slightly arcuate.

erect or ascending, branched from base or nearly so;

branches straight or slightly arcuate (proximal ones sometimes almost prostrate).

alternate;

blade filiform to narrowly linear, 1–2 mm wide, less than 1 mm wide in herbarium specimens, usually not fleshy, sometimes semi-amplexicaul at base, apex with soft bristle (rarely subspinescent).

(especially proximal ones) mostly opposite;

blade linear, usually more than 1.5 mm wide in herbarium specimens, fleshy, distinctly swollen or ovate at base, apex mucronulate, not spinose.

not interrupted, dense, 1-flowered (rarely 2–3-flowered), often also in axils of proximal leaves and branches, lower ones tightly enclosed in bracts and bracteoles, forming gall-like caducous balls at maturity;

bracts alternate, strongly imbricate and appressed at maturity, base not distinctly swollen, apex acuminate into subulate spine.

distinctly interrupted, 1-flowered;

bracts alternate or almost opposite, not imbricate, horizontally reflexed at maturity, swollen at base, abruptly narrowing into mucronulate nonspinose apex.

bracteoles becoming connate basally and adnate to perianth segments;

perianth segments wingless or with narrow, erose wing at maturity, apex acute, weak and flaccid, glabrous; fruiting perianth ca. 2–5 mm diam. 2n = 18.

bracteoles distinct, not adnate to perianth segments;

perianth segments wingless or with rudimental triangular tubercles at maturity, margins crenate or pectinate-ciliate apically, glabrous; fruiting perianth ca. 3–6(–7) mm diam. 2n = 18.