Alkali centaury

Erythraea trichantha Grisebach, Gen. Sp. Gent., 146. 1838; Centaurium trichanthum (Grisebach) B. L. Robinson

Herbs annual, 5–35(–45) cm. Stems 1(–5), branching near or above 1/3 of height, occasionaly lower. Leaves cauline; blade ovate to lanceolate, distal sometimes linear, 10–40 × 1–11 mm, apex acute. Inflo­rescences ± dense, proximally dichasial, distally some­times monochasial, usually corymboid cymes; proximal flowers sessile or pedicels to 3(–6) mm, distal flowers usually sessile. Flowers 5-merous; calyx 8–14 mm; corolla 12–22 mm, lobes lanceolate, (3–)5–10 mm, apex acute to acuminate; stigmas 2, cuneate, closely appressed and sometimes appearing as 1. Seeds dark brown. 2n = 34.

Flowering spring–summer. Alkaline and saline flats, moist sites in chaparral and open woods, often in ser­pentine soils; 0–800 m; Calif.

The inflorescence of Zeltnera trichantha is generally corymboid, but the level at which plants first branch varies. Plants branching at or near the base, so that the whole plant above ground is obconic, plants branching only in the upper fifth or less, and a complete range of intermediates may occur within a single population.

Unequivocal Zeltnera trichantha occurs in the Inner North Coast Range and San Francisco Bay region of California, from San Mateo and Stanislaus counties north to Tehama County, often on alkaline flats and in serpentine soils. This species can generally be recognized by a distinctive combination of relatively dense, obconic inflorescences; all flowers sessile or on true pedicels usually less than 4 mm, rarely to 6 mm; narrow, acute to acuminate corolla lobes, notably contrasting with the obtuse or abruptly acute corolla-lobe apices prevalent among the other Zeltnera species in the flora area; styles that are longer and more slender than those of most Zeltnera species, often extending 6–11 mm beyond the throat of the corolla; and cuneate stigmas 0.2–0.3 mm wide at the summit, which remain more or less appressed to each other throughout much of the life of the flower. Basal leaves are absent at flowering time. Usually, but less consistently, the cauline leaves are elliptic, widest near the middle, tapering toward the base, and acute to acuminate at the apex. Elsewhere in California, plants of Z. venusta with narrow corolla lobes often resemble Z. trichantha to various degrees. These species are contrasted in the discussion of Z. venusta. Other species, notably Z. muehlenbergii, occasionally approach Z. trichantha in habit, but, like Z. venusta, differ in having two distinctly separate, fan-shaped stigmas on a shallowly cleft style.