Calycadenia micrantha R. L. Carr & G. D. Carr

Calycadenia micrantha is most closely related to variants of C. truncata and is found in the North Coast Range from Trinity County to Lake and Colusa counties. Calycadenia truncata subsp. microcephala H. M. Hall ex D. D. Keck may be a synonym of C. micrantha. D. D. Keck (1960b) reported this to be on the east slope of the Santa Lucia Mountains of Monterey County.

Plants 10–50 cm (relatively slender); self-compatible. Stems (often purplish, especially distally, slender, usually less than 3 mm diam. at bases) branched (branches often relatively many, usually from near midstems, arcuate to ascend-ing), glabrous. Leaves mostly alternate, 2–5 cm (proximal), hispidulous and ± long-hairy (especially margins and adaxial faces). Heads borne singly or in ± spiciform arrays (1–3 per node, ± sessile). Peduncular bracts lance-oblong to linear, 2–4 mm (nearly terete to strongly flattened, glabrous or hispid overall, sometimes pectinate-fimbriate), apices ± rounded, tack-glands usually 1 (terminal). Phyllaries 4–5 mm, abaxial faces glabrous or ± hispid distally or sparsely bristly, shaggy long-hairy on margins distally, tack glands 0(–1) (terminal). Paleae 5–6 mm. Ray florets 1–3(–6); corollas bright yellow, tubes 1–1.5 mm, laminae 2–2.5(–3) mm (central lobes smaller than laterals, oblong to narrowly triangular, symmetric, widest at bases, laterals asymmetric, sinuses ¹/4 laminae). Disc florets 1–3; corollas yellowish, 3–4 mm. Ray cypselae ca. 3 mm, rough-wrinkled, glabrous. Disc cypselae ca. 3 mm (seldom formed, terete and tapered toward bases, smooth to ± ridged, glabrous); pappi 0. 2n = 14.

Calycadenia micrantha is an uncommon species of flowering plant in the family Asteraceae known by the common name small-flowered calycadenia. It is endemic to California, where it is known from about 13 occurrences that are widely spread over several counties, including Napa, Siskiyou, Shasta, Mendocino, Trinity, and Monterey Counties, with several populations known in Lake County. It was described to science as a species in 2004. Some specimens of the plant had previously been included within the description of its relative, Calycadenia truncata. The fact that it has been found in relatively far-flung locations suggests it could easily be present in other areas between them and, as a newly classified species, has simply not been reported yet.

This annual plant produces a slender purplish stem 10 to 50 centimeters tall. The hairy leaves are 2 to 5 centimeters long. The inflorescence is a single flower head or small cluster of heads, each with 1 to 6 three-lobed yellow ray florets. Unlike other Calycadenia species, this plant is self-compatible, or able to fertilize itself.