Flora of North America species comparison

The name Centaurium muehlenbergii has sometimes been misapplied to Zeltnera davyi, with true Z. muehlenbergii then being called C. floribundum (J. S. Pringle 2010b).

The distinctly keeled calyx lobes cause the calyces of Zeltnera davyi to appear greater in diameter than those of related species and ovoid to ellipsoid rather than nearly cylindric. The combination of this calyx morphology and the proportionately wide, relatively deeply pigmented corolla lobes (usually evident in herbarium specimens) gives the flowers of Z. davyi a distinctive aspect.

Zeltnera davyi and Z. muehlenbergii are sometimes similar in habit. Medium-sized plants of Z. davyi are usually several-stemmed from the base, whereas that pattern is much less common in Z. muehlenbergii. Zeltnera davyi usually differs from Z. muehlenbergii in the presence of elliptic to ovate leaves over 5 mm wide (except on the smallest plants) well into the inflorescence; consistently present pedicels 4–30 mm long; calyx lobes with keels proximally 0.3–0.6 mm wide; and ovate-elliptic corolla lobes 3–7 × 2–3 mm. In Z. muehlenbergii, elliptic to narrowly ovate leaves, when present, are usually limited to the proximal one-third or less of the plant, with the distal leaves being narrower, and the corolla lobes are elliptic-oblong, 2–7 × 1–2 mm (J. S. Pringle 2010b).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

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).

(Discussion copyrighted by Flora of North America; reprinted with permission.)