Gypsum centaury

Centaurium maryannianum B. L. Turner, Phytologia 75: 269, fig. 4. 1993 (as maryannum)

Herbs annual, 3–20 cm. Stems 3–30, branching throughout. Leaves: basal present at flow­ering; blade narrowly oblan­ceolate to obovate, 20–50 × 2–8 mm, apex obtuse to acute; cauline blades oblanceolate (proximal) to narrowly oblong-lanceolate or linear (distal), 15–25 × 1–4 mm, apex obtuse (proximal) to acuminate (distal). Inflo­rescences dichasial cymes; pedicels 5–20 mm. Flowers 5-merous; calyx 7–10 mm; corolla 14–22 mm, lobes ovate-elliptic, 6–11 × 1–4.5 mm, apex acute; stigma 1, 2-lobed, lobes fan-shaped, tardily diverging. Seeds black. 2n = 42.

Flowering spring–summer. Roadsides, sand hills, rocky ridges, other open sites in gypsum soils; 900–1700 m; N.Mex., Tex.

Zeltnera maryanniana is known only from gypseous habitats in southeastern New Mexico and trans-Pecos Texas, but might be expected in northern Chihuahua, Mexico.

Prior to its recognition as a species in 1993, specimens of Zeltnera maryanniana were identified as Centaurium beyrichii, C. calycosum in the broad sense, or C. texense, or as hybrids between species that do not occur in the range of Z. maryanniana. In aspect, Z. maryanniana is similar to Z. beyrichii, from which its range is separated by about 650 km. Its flowering stems arise from a dense tuft of basal leaves and rosettes that still are green at flowering time, whereas such basal leaves are usually more or less withered when plants of Z. beyrichii are in flower. Nearly all of the leaves of Z. maryanniana are distinctly wider than the stem diameter, whereas the mid-stem and distal leaves of Z. beyrichii are often only about as wide as the stem. Zeltnera maryanniana differs from Z. texensis in its tufted stems, and from both Z. beyrichii and Z. texensis in its single stigma and black seeds. The corolla lobes of Z. maryanniana are elliptic and proportionately wider than those of Z. beyrichii and Z. texensis. Zeltnera maryanniana further differs from all other Zeltnera species in having filaments expanded at the base (G. Mansion 2004).

Plants of Zeltnera maryanniana sometimes flower again after the fruits have matured on the first stems, but no specimens seen in studies for this flora show evidence of a truly perennial habit. Plants of some Mexican species of Zeltnera likewise sometimes flower a second time before dying (C. R. Broome 1973).