Hybrid dogbane, Apocyn moyen

Apocynum medium Greene

Herbs 2–5 dm. Stems glabrous or occasionally eglandular-pubescent. Leaves spreading to ascending; petiole 3–5 mm, glabrous; blade ovate to oblong-lanceolate, 3–6(–8) × 1.5–3(–5) cm, mostly less than 2 times as long as wide, membranous, base rounded to cuneate, margins weakly to strongly revolute, apex acute to rounded, usually apiculate, surfaces glabrous or eglandular-pubescent abaxially, glabrous or sparsely eglandular-pubescent adaxially. Inflorescences usually exceeding foliage; peduncle 1–2.5 cm, sparsely pubescent. Pedicels 1.5–7 mm, glabrous or sparsely pubescent. Flowers: calyx lobes lanceolate to oblong, 1.5–3 × 0.8–1 mm, glabrous or sparingly pubescent; corolla pink or white tinged with pink, glabrous abaxially and adaxially, tube 4–5 × 3.5–5 mm, 1.5–2 times as long as calyx lobes, lobes spreading or recurved, triangular-ovate, 2–3 × 0.8–1.2 mm. Follicles 70–150 × 2–3 mm. Seeds 3–4 × 0.4–0.6 mm.

Flowering summer–fall; fruiting summer–fall. For­ests, woodlands, fields, river terraces, lakeshores, road­sides; 10–2600 m; Alta., B.C., Man., N.B., Nfld. and Labr., N.S., Ont., Que., Sask.; Ariz., Ark., Calif., Colo., Conn., Del., D.C., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico (Coahuila).

Apocynum × floribundum (as A. medium) was con­sidered by R. E. Woodson Jr. (1930) to be of hybrid origin, as were many of the taxa that he described in Apocynum. In a classic study, E. Anderson (1936b) investigated the possibility of a hybrid origin for A. ×floribundum by growing seeds from plants identified by Woodson as A. androsaemifolium, A. cannabinum, and A. × floribundum. The offspring of the putative parental species bred true and had high pollen viability, while the progeny of the putative hybrids were quite variable in their morphological characteristics and had lower pollen viability, leading Anderson to conclude that A. × floribundum was truly of hybrid origin. More recently, S. A. Johnson et al. (1998) found that allozyme data, as well as statistical analyses of various morphological characters, also support the hypothesis of a hybrid origin for A. × floribundum.