Flora of North America species comparison

The name Centaurium muehlenbergii has often been misapplied to C. tenuiflorum in the flora area (J. S. Pringle 2010b). This error accounts for reports of C. muehlenbergii in Louisiana, Mississippi, and Texas. The name C. floribundum, although typified by specimens referable to Zeltnera muehlenbergii, has also been misapplied to C. tenuiflorum, hence comments by some authors that C. floribundum should perhaps be included in C. tenuiflorum. This complex nomenclatural history has caused confusion with regard to the conservation status of plants called Centaurium or Z. muehlenbergii. From studies for this flora work, it appears that the true Z. muehlenbergii is appropriately of conservation concern.

The inflorescences of Zeltnera muehlenbergii are relatively open, in contrast to the dense, corymboid dichasia of Centaurium tenuiflorum. The proximal branching of the larger plants of Z. muehlenbergii is usually dichasial, with the central flower sessile or on a pedicel to 5 mm long or occasionally to 12 mm. The distal branching is mostly monochasial, with a branch developing only on one side of each flower; the inflorescences of small plants are often monochasial throughout. The flowers at the distal divisions are sessile or on pedicels to 4 mm. Both C. tenuiflorum and C. pulchellum, which are sometimes similar in aspect, differ from Z. muehlenbergii in the style and stigma characters noted in the descriptions of the respective genera (J. S. Pringle 2010b).

Some plants of Zeltnera davyi and exceptionally small plants of Z. exaltata look much like Z. muehlenbergii but consistently have proximal pedicels more than 4 mm long and often more than 12 mm. Even on small plants the pedicels of Z. exaltata are often longer than the flowers.

The name Monterey centaury is sometimes associated with this species, but that vernacular name came into use when the name Centaurium muehlenbergii was being misapplied to Zeltnera davyi. True Z. muehlenbergii has rarely been found as far south as the northern shore of Monterey Bay (J. S. Pringle 2010b).

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

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.

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