Montana Field Guide

PLANTS: Small, annual forbs with fibrous roots and a single, but sometimes branched stem, 10 to 60 cm tall. Across its range, the species exhibits great variation in the number of stems, presence or absence of basal leaves at flowering, and in leaf width. Sources: Lesica et al. 2022; Pringle in Flora of North America [FNA] 2023.

LEAVES: Basal and cauline (stem) present and similar, or larger. Basal leaves sometimes whither by flowering. Leaves arranged opposite on stem. Lower (or all) leaf blades oblong-elliptic to lanceolate and upper blades linear, in shape, 1-3 cm long. Sources: Lesica et al. 2022; Pringle in FNA 2023.

INFLORESCENCE: Narrow cyme with two lateral axes, producing few pink to white flowers – salverform in shape. Calyx: 4, linear, 6-11 mm long, and united at base. Corolla: 4, 10-20 mm long. Petal lobes are lanceolate to oblong or narrowly elliptic-obovate, and about half as long as the tube - 2.5-6 mm by 0.8-2.5 mm; tips are truncate to rounded or obtuse. Tube is 6-13 mm long. Stamens: Exserted. Pistil: Single with 1 style and stigma. Sources: Lesica et al. 2022; Pringle in FNA 2023.

TAXONOMY & NOMENCLATURE
The native North American species have been transferred from the genus Centaurium to Zeltnera - in the Flora of North America and Flora of the Pacific Northwest - 2nd Edition. The taxonomic shift is based on molecular phylogenetic studies (Mansion 2004; Mansion and Struwe 2004; Pringle in FNA 2023).
The revised treatments separate Centaurium and Zeltnera on the following morphology:

Centaurium
* Non-native species to North America
* Basal Leaves: rosette usually present during flowering
* Flowers: white to yellowish-pink
* Pistil with 2 stigmas crescent-shaped (elliptic to ovate to orbiculate) – as long as or longer than wide.
* Capsule cylindric

Zeltnera
* Native species to North America
* Basal Leaves: rosette absent by flowering
* Flowers: pink, rose-violet, or white.
* Pistil with 2 stigmas that are crescent to fan-shaped or 1 stigma with 2 fan-shaped lobes – as wide as or wider than long
* Capsule fusiform (ovoid to ellipsoid)

Centaurium comes from the Greek word kentauros meaning "centaur" which alludes to the plant’s supposed medicinal use by Chiron in Greek mythology (Pringle in FNA 2023).

Flowering from spring to early fall (range-wide). Montana’s populations were found in late June and late August.

Members of the Gentian Family (Gentianaceae) have opposite leaves, glabrous foliage, and flowers with 4 to 5 tubular petals of equal size. Traditionally, the genus Centaurium is distinguished from other family members by a salverform flower – where lobes spread at right angles to the tube, a long and narrow corolla tube, and the of lack membranous tissue between the petals.

The Manual of Montana Vascular Plants (Lesica et al. 2022) retains a traditional taxonomic treatment:

Western Centaury - Centaurium exaltatum, native, SOC
* Leaves: Basal rosette of basal leaves that wither by flowering time; thus, appearing all cauline
* Inflorescence: Little branched, few flowered
* Seeds: Dark reddish brown to nearly black

Common Centaury - Centaurium erythraea, non-native
* Leaves: Small rosette of basal leaves present during flowering and anthesis
* Inflorescence: Densely branched, many flowers
* Seeds: Brown

Across its range, Western Centaury grow in stream banks, marshes, lakeshores, along margins of hot springs and vernal pools to alkaline wetlands surrounded by desert (Pringle in FNA 2023). In Montana, plants are found in moist alkaline soil of shallow wetlands in the plains zone (Lesica et al. 2022).

Plants reproduce by seed.

FRUITS & GENETICS
The fruit is a capsule. Capsule is cylindric, 7-15 mm long. Seeds are dark reddish brown to nearly black. Seeds are diploid with a chromosome number of 2n = 40 or 74 (Mansion and Zeltner 2004). In general, plants at the southern parts of the range have lower chromosome numbers than those in the northern portions (Mansion and Zeltner 2004).

It is thought that Western Centaury plants require some type of disturbance with soils or hydrology to sustain their populations.

An overall State Threat Score of “Very High” is assigned to Western Centaury (see Conservation Status Summary, 2025). A population of flowering and vegetated individuals emerged in 2017 during the construction of a wetland mitigation site. Although unknown but assumed that seeds were present and that disturbance promoted germination. During annual monitoring the population was not observed from 2018 to 2024. It is assumed that the species requires a disturbance regime to persist, such as periodic flooding and drying or soil disturbance to reduce plant competition. More information is needed to validate these assumptions.