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Published In: Annals of the Missouri Botanical Garden 22(3): 651. 1935. (Ann. Missouri Bot. Gard.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/28/2009)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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2. Triosteum aurantiacum E. P. Bickn. var. illinoense (Wiegand) E.J. Palmer & Steyerm. (red-fruited horse gentian)

Triosteum illinoense (Wiegand) Rydb.

Map 1435, Pl. 337 f, g

Stems 0.3–1.0 m long, moderately to densely pubescent with straight, more or less spreading, bristly hairs 1.5–3.0 mm long, these sometimes mixed with sparse or rarely denser, short (0.3–0.5 mm), softer hairs that are mostly minutely gland-tipped. Leaf pairs not perfoliate or 1–3 median pairs weakly perfoliate, these 1–2 cm wide at the base. Leaf blades 9–20 cm long, 4–9 cm wide, oblanceolate to obovate or elliptic, those of the largest leaves occasionally slightly fiddle-shaped, the nonperfoliate leaves tapered at the base, sometimes to an indistinct, broadly winged petiolar base, tapered to a sharply pointed tip, the margins with relatively dense, stiff, ascending hairs, the upper surface moderately pubescent with short, straight, appressed hairs, the undersurface moderately to densely pubescent with short, soft, spreading hairs mostly along the veins. Flowers 1 or less commonly 2 or 3 per leaf axil (2–6 per node). Paired bracts subtending each flower sometimes longer than the ovary but shorter than the flower (including the calyx and corolla), linear to narrowly lanceolate. Calyx lobes 8–15 mm long, the margins with dense, stiff, bristly, longer and shorter hairs, the inner and outer surfaces with scattered, short hairs. Corollas 8–15 mm long, dull red to purplish red, narrowly funnelform, the mouth relatively strongly oblique, the outer surface with gland-tipped hairs. Styles not or only slightly exserted (less than 3 mm beyond the corolla lobes). Fruits 7–10 mm in diameter, red (may be orange when not fully mature), usually densely hairy at maturity. April–July.

Scattered, mostly in the eastern half of the state, and uncommon in the northwestern quarter mostly in counties along the Missouri River (Nebraska to Oklahoma east to Pennsylvania and West Virginia). Bottomland forests, mesic upland forests, and bases and ledges of bluffs.

Triosteum aurantiacum and T. perfoliatum differ in several subtle characters, but all of these are variable, and specimens (especially vegetative ones) are sometimes impossible to identify with certainty. Some authors have treated the former taxon as T. perfoliatum var. aurantiacum (E.P. Bickn.) Wiegand. It is not clear whether the difficulty in distinguishing the taxa is merely due to the variability of the characters, or whether there is actual intergradation due to natural hybridization between them. Lane (1954) suggested that a few specimens collected by Julian Steyermark in Chariton and Howard Counties might possibly represent hybrids between T. aurantiacum (as T. illinoense) and T. perfoliatum, but these have been redetermined in the present work as merely examples of the latter species. Steyermark (1963), who collected the two species occasionally in mixed populations, nevertheless felt that the degree of intergradation in the field was very small.

Most authors have recognized three variants within the T. aurantiacum complex, either as varieties of T. aurantiacum or as separate species. Because there is considerable morphological overlap between the phases in some eastern portions of the species range, they are best treated as varieties until more intensive studies can be carried out. Plants of var. illinoense are the only phase found in Missouri, with the remainder of the complex occurring to the east of the state. They are unique in their stems having mostly relatively long (to 3 mm), shaggy hairs, in contrast to the other varieties, which have mainly shorter (0.5–1.5 mm) hairs. Among eastern North American plants, those assigned to var. aurantiacum have the leaves hairy on the undersurface, whereas in var. glaucescens Wiegand the leaves are glabrous or nearly so on the undersurface (Gleason and Cronquist, 1991).



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