Hesperevax caulescens (Benth.) A. Gray

Hesperevax caulescens occurs mainly in the Sacramento and northern San Joaquin valleys, with southern outliers in the southern San Joaquin and upper Salinas River valleys and the Otay Mesa area of San Diego County. The Otay Mesa populations are thought to have been naturalized (R. M. Beauchamp 1986) and are now considered extirpated. An 1869 specimen from northern Oregon is likely either mislabeled or from an introduction that did not persist.

Caulescent forms are scattered among predominantly stemless populations throughout the northern range of Hesperevax caulescens. The tallest forms (Evax involucrata) are often grayer and more densely lanuginose. The various growth forms appear to be environmentally induced and taxonomically insignificant. Plants from the southern outliers are all stemless, tend to be smaller in sizes and numbers of structures, and may warrant varietal status (J. D. Morefield 1992c). A malformed plant from Merced County appears to have been a hybrid between H. caulescens and Psilocarphus oregonus.

Hesperevax caulescens may soon be of conservation concern in California as its vernal pool habitats continue to decline. The vernacular "hogwallow starfish" is widely used for H. caulescens by students and enthusiasts of California’s vernal pools.

Plants (2–)3–8(–17) cm. Stems usually 0, sometimes 1–4, erect to decumbent; branches 0 or proximal. Leaves basal or cauline, petiolate, distal congested, larger than proximal (if any), largest (25–)33–90 × 7–20 mm; petioles: lengths 2–3 times blade lengths, bases thickened, indurate; capitular leaves (6–)10–20 per glomerule, whorled, mostly spreading, unlike pistillate paleae. Heads terminal in dense glomerules (10–25 mm diam.) of 10–40+ not mixed with leaves, never in axils, ± obpyramidal, 3–5 × 2.5–4 mm, heights 1–1.5 times diams. Receptacles of adjacent heads proximally connate, 0.4–0.7 × 0.5–0.7 mm. Pistillate paleae in 2–4 series, ± vertically ranked, broadly spatulate, 2.5–4.5 mm. Staminate paleae surpassing pistillate, 3–3.9 mm, lengths 0.7–0.9 times head heights, apices spreading. Functionally staminate florets 3–6; corollas 1.1–1.6 mm. Cypselae mostly 1.5–2 mm.

Psilocarphus caulescens Bentham, Pl. Hartw., 319. 1849; Evax caulescens (Bentham) A. Gray; E. caulescens var. humilis (Greene) Jepson; E. involucrata Greene

Hesperevax caulescens is a small flowering plant in the family Asteraceae. One common name for the plant is hogwallow starfish, as it is a somewhat flat, star-shaped plant which grows in mud. Another common name is dwarf dwarf-cudweed, as the three members of genus Hesperevax are known as dwarf-cudweeds and this species is smaller than the others. It may also be called involucrate evax, since its former Latin name was Evax involucrata. This annual plant is a member of the vernal pool plant community in California, where it is possibly an endemic species, although its range might extend into Baja California. The hogwallow starfish radiates pale green spoon-shaped leaves in a basal rosette and extends a short erect stem. The flowers are less than two millimeters wide. This species grows along the outskirts of vernal pools in areas which have dried.

Hesperevax caulescens là một loài thực vật có hoa trong họ Cúc. Loài này được (Benth.) A.Gray mô tả khoa học đầu tiên năm 1868.