Triosteum aurantiacum E.P. Bicknell

Red-Fruited Horse Gentian

Triosteum aurantiacum plant

Family - Caprifoliaceae

Stems - Erect, to 1 m, pubescent with spreading bristly hairs, sometimes also with shorter, soft, glandular hairs.


Leaves - Obovate, elliptic, or fiddle-shaped, tapered at base, not or only weakly perfoliate, variously pubescent.


Inflorescence - Flowers borne in leaf axils, most commonly 1 and less commonly 2-3 per axil.

Calyx - Lobes 8-15 mm long, margins and surfaces moderately pubescent.


Flowers - Corollas 8-15 mm, dull red to purplish red, funnelform, with oblique mouth, surface with gland-tipped hairs.


Fruits - Spherical, 7-10 mm in diameter, with persistent calyx lobes, red (orange when not fully mature), usually densely hairy at maturity.


Flowering - April - July.

Habitat - Forests, bases and ledges of bluffs.

Origin - Native to U.S.

Other info. - The colloquial names for the horse gentians are problematic, since neither the flowers nor the fruits consistenly comply with the color epithets. The flowers of "yellow flowered" horse gentian can actually be red, and as shown in the photos above, immature fruits of the "red fruited" horse gentian are actually orange. This is yet another example of why scientific names are to be preferred.
In some cases, determination of Triosteum to species can be difficult, since most of the characters used in identification are variable and show some overlap between species. It has also been suggested that intermediate forms may represent hybridization events.

Photographs taken at Cuivre River State Park, Lincoln County, MO, 5-9-2011, at Matson Hill County Park, St. Charles County, MO, 4-9-2012 and 5-12-2014, and at Glassberg Conservation Area, Jefferson County, MO, 7-10-2017 (SRTurner).