Herbs annual, 3–30(–40) cm. Stems usually 1, occasionally 2–4, simple or variously branching. Leaves: basal present or absent at flowering but not forming well-developed rosette; blade obovate to oblong, 15–25 × 3–15 mm, apex rounded to obtuse; cauline blades narrowly elliptic-ovate to elliptic-lanceolate, 10–25 × 2–9 mm, apex obtuse or distal leaves of large plants acute. Inflorescences ± open, distally or completely monochasial cymes; proximal flowers in center of cyme divisions sessile or pedicels to 12 mm, distal flowers generally sessile or pedicels to 4 mm. Flowers 5-merous; calyx 8–13 mm; corolla 12–19 mm, lobes oblong-lanceolate to narrowly elliptic, 2–7 mm, apex obtuse to subacute; stigmas 2, fan-shaped. Seeds brown.

Phenology: Flowering early summer–early fall.
Habitat: Wet meadows, marsh edges, wet openings in woods, seeps, often in serpentine soils.
Elevation: 0–1600 m.

Distribution

• Generated Map
• Legacy Map

B.C., Calif., Idaho, Oreg., Wash.

Discussion

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).

Selected References

None.

Lower Taxa

None.