4. Triosteum L. (horse gentian)

Plants perennial herbs. Stems erect or ascending, 2–8 mm in diameter, solitary or few to several, unbranched, sometimes hollow between the nodes, moderately to densely pubescent with shorter and/or longer, spreading hairs, some of these sometimes gland-tipped. Leaves sessile or with indistinct, broadly winged petioles, perfoliate or those of each pair connected by a ridge around the stem. Stipules absent. Leaf blades simple, unlobed or the largest leaves occasionally irregularly scalloped, with shallow, rounded lobes, or somewhat fiddle-shaped, oblanceolate to elliptic, obovate, or oblong-obovate, the margins otherwise entire. Flowers solitary or in dense clusters of 2–6 in the axils of the upper leaves, clusters on each side of the stem sometimes with a leaflike bract, the individual flowers subtended by a pair of leaflike bractlets, these longer than the ovary. Calyx lobes 7–15 mm long, linear to narrowly triangular or narrowly lanceolate. Corollas 9–20 mm long, zygomorphic, somewhat funnelform with a curved tube, a slightly to strongly oblique mouth, and 5 relatively shallow lobes, these oblong to nearly circular and sometimes somewhat overlapping, the overall corolla yellow or red. Style 10–23 mm long. Fruits drupes, appearing berrylike but relatively dry and mealy, 5–10 mm in diameter, more or less spherical, orangish yellow to orangish red or red and occasionally greenish-tinged at maturity. Nutlets usually 3, 4.5–9.5 mm long, more or less elliptic in outline, somewhat 3-angled, with a prominent, blunt keel on the ventral side and rounded with 4 or 5 prominent, rounded longitudinal ridges on the dorsal side, the surface appearing somewhat encrusted or fibrous between the ribs, tan to yellowish brown or reddish brown. Five or 6 (possibly more) species, eastern North America, Asia.

It should be noted that some Asian species of Triosteum have terminal inflorescences and that various non-Missouri species differ in fruit color (Gould and Donoghue, 2000). Ripe fruits of Triosteum spp. have been dried and roasted for use as a coffee substitute (Ferguson, 1966a).