Muhlenberg's centaury (Centaurium muehlenbergii COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:
Centaurium muehlenbergii (Griseb.) Wight ex Piper
Synonyms:
Zeltnera muehlenbergii (Griseb.) G. Mans; Erythraea muehlenbergii Griseb.; C. curvistamineum (Wittr.) Abrams; C. floribundum (Benth.) B.L. Rob. An alternative spelling for the specific epithet is “muhlenbergii” (Hitchcock and Cronquist 1973).
English common names:
Muhlenberg's centaury, Monterey centaury, June centaury
Family:
Gentianaceae (Gentian Family)
Major plant group:
Eudicot flowering plant

Centaurium is generally viewed as a taxonomically difficult genus (Cronquist et al. 1984; Hickman 1993; Turner 1993; Holmes and Wivagg 1996; G. Mansion, pers. comm. 2001; J. Pringle, pers. comm. 2001). Further work may be needed to clarify the taxonomic status of Centaurium muehlenbergii. The name C. muehlenbergii may have been misapplied to C. exaltatum, C. tenuiflorum, C. davyi, C. erythraea, C. pulchellum, and possibly three or four other species (J. Pringle, pers. comm.). However, C. tenuiflorum and C. davyi occur in California; C. erythraea and C. pulchellum are both exotic in North America with the latter only occurring in eastern Canada and the eastern U.S. G. Mansion has suggested recognition of a “Centaurium muehlenbergii complex” which includes C. curvistamineum, C. floribundum, and C. tenuiflorum. These three taxa are included as synonyms of C. muehlenbergii in Kartesz (1999). Centaurium muehlenbergii is the only element of this complex in Canada. Mansion also suggests a hybrid origin of C. muehlenbergii, involving C. erythraea and C. tenuiflorum (G. Mansion, pers. comm. 2001).

Due to the confusion around the taxonomy of Centaurium muehlenbergii it is difficult to ascertain which literature references to C. muehlenbergii pertain to the “true” rare plant, and which references have been misapplied.

Morphological description

Centaurium muehlenbergiiis a small annual with pink or white flowers that blooms from June to August (Fig. 1). Plants range in height from 3-30 cm (individuals in B.C. are generally only 4-8 cm). The stems are hairless and have opposite leaves. Flowers are small and tube-shaped, with anthers that extend well beyond the edge of the tube and are thus easily visible. The flower stalk is shorter than the tube formed by the sepals, which in turn are shorter than the flower tube. Each flower produces numerous small (<0.5 mm) brown seeds (Hitchcock and Cronquist 1973, Douglas et al. 1999).

Two other species of centaury are recognized in B.C. Common centaury (C. erythraea), a Eurasian exotic, has a well-developed basal leaf cluster and the flowers are unstalked (or nearly so). Western centaury (C. exaltatum) which occurs only in southcentral British Columbia and not west of the Cascades, lacks basal leaves; the flower stalk is also much longer than the sepals, and the sepals are as long or longer than the flower tube (Douglas et al. 1999).  Centaurium muehlenbergiiis readily distinguished from these two species on the basis of the above characteristics.

Figure 1. Illustration of Centaurium muehlenbergii. Shown are plant growth form, close-up of a flower and bud and of a single stamen (bottom right). Line drawing from Hitchcock et al. 1959 and Douglas et al. 1999, reproduced with permission from Universityof Washington Press.

Figure 1. Illustration of Centaurium muehlenbergii. Shown are plant growth form, close-up of a flower and bud and of a single stamen (bottom right). Line drawing from Hitchcock et al. 1959 and Douglas et al. 1999, reproduced with permission from Universityof Washington Press.

Genetic description 

The population genetic structure of Centaurium muehlenbergii in Canada has not been assayed. However, given the species’ lack of specialized dispersal mechanisms and the fairly large distances (5 to 80 km) that separate the three C. muehlenbergii populations on southeastern Vancouver Island, genetic interchange among populations likely occurs infrequently, if at all. Given the apparent small effective sizes of most populations, loss of vigour due to local inbreeding effects could be a limiting factor for this species in Canada. Decreased fecundity and survival in relation to genetic diversity and population size were found in populations of Gentiana pneumonanthe (marsh gentian), a rare plant of European calcareous grasslands (Oostermeijer et al. 1994). This example involves a species within the same family as C. muehlenbergii.

Designatable units

A single designatable unit is recognized for Centaurium muehlenbergii in Canada because there are only three extant sites and these occur within a single ecozone.

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