Rock or mountain centaury, mountain-pink, quinineweed

Erythraea beyrichii Torrey & A. Gray in R. B. Marcy, Explor. Red River Louisiana, 291, plate 13. 1853, based on E. trichantha Grisebach var. angustifolia Grisebach in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 9: 60. 1845; Centaurium beyrichii (Torrey & A. Gray) B. L. Robinson

Herbs annual or perennial, 10–45 cm. Stems 1–20 from crown, if 1, dividing near base into ± equal branches, these much-branched distally. Leaves: basal usually withered or absent by flowering, similar to cauline; cauline blades narrowly linear-oblanceolate or linear (proximal) to filiform (distal), 10–30 × 1–2(–3) mm, apex acute. Inflorescences dense, much-branched, dichasial cymes; pedicels 3–15 mm. Flowers 5-merous; calyx 7–11 mm; corolla 15–30 mm, lobes narrowly oblong-lanceolate to linear, 7–16 × 1–2 mm, apex acute; stigmas 2, clavate to narrowly fan-shaped, ± tardily diverging. Seeds dark brown. 2n = 40, 82.

Flowering spring–summer. Wet, gravelly or rocky places, usually in calcareous soils; 100–700 m; Okla., Tex.

Reports of Zeltnera beyrichii (as Centaurium) from Arkansas have been based only on the provenance of the type specimen, given as Arkansas Territory but probably in present-day Oklahoma. New Mexico plants have been separated as Z. maryanniana. A specimen at ASU from Coahuila, Mexico, appears to represent this species but requires further study.

Plants of Zeltnera beyrichii often have 20 or more stems from the base. These stems are much-branched. The larger plants usually bear over 200 flowers and sometimes over 1000. Zeltnera beyrichii is often described as an annual, but C. R. Broome (1973) characterized it as a true perennial, which perennates by the production of vegetative shoots from the roots.

Although the style of Zeltnera beyrichii is initially deflexed like those of other large-flowered Zeltnera species and the stigmas are well separated from the anthers when the latter dehisce, the stamens are radially divergent at anthesis rather than all being curved to one side (C. R. Broome 1973).

C. R. Broome (1973, 1978) considered Zeltnera beyrichii a probable allopolyploid derivative of Z. calycosa and Z. texensis.