Showy milkweed, asclépiade belle, belle asclépiade

Herbs. Stems 1–few, erect, unbranched (rarely branched), 30–125 cm, tomentose to puber­ulent with curved tri­chomes, not glaucous, rhizoma­tous. Leaves opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole, sometimes also in axil; petiole 4–12 mm, tomen­tose to pilose; blade lanceolate or ovate to oblong, 6–20 × 2–14 cm, chartaceous, base rounded to truncate or cordate, margins entire, apex acute to obtuse, some­times mucronate, venation faintly brochidodromous, surfaces tomentose to pilose, margins ciliate, 6–32 lam­inar colleters. Inflorescences extra-axillary, pedun­cu­late, 3–34-flowered; peduncle 1–10 cm, densely tomen­tose, with 1 caducous bract at the base of each pedicel. Pedicels 13–30 mm, densely tomentose. Flowers erect to pendent; calyx lobes elliptic, 4–8 mm, apex acute, tomentose; corolla dark pink (rarely pale), lobes reflexed with spreading tips, elliptic, 9–12 mm, apex acute, densely pilose abaxially, hirtellous at base adaxially; gynostegial column 0.5–1 mm; fused anthers green and brown, truncately obconic, 2.5–3 mm, wings right-triangular, open, widely so at base, apical append­ages deltoid; corona segments pale pink to nearly cream, sessile, scoop-shaped, 9–15 mm, exceeding style apex, apex truncate with proximal tooth on each side and long-attenuate, flared, glabrous, internal appendage sub­ulate, exserted, sharply inflexed over style apex, gla­brous; style apex shallowly depressed, green to cream or pink. Follicles erect on upcurved pedicels, lance-ovoid, (5–)9–12 × 2–3 cm, apex long-attenuate, muricate or smooth, densely tomentose. Seeds ovate, 7–9 × 4–5 mm, margin winged, faces rugulose; coma 2.5–3 cm. 2n = 22.

Flowering (Apr–)May–Sep; fruiting Jul–Oct. Slopes, flats, hills, valleys, canyons, coulees, streamsides, lake and pond edges, ditches, swales, seeps, granite, basalt, schist, pumice, serpentine, alluvium, clay, sandy, silty, rocky, and saline soils, pine and mixed-conifer forests, oak and pine woodlands, chaparral, riparian woods, shrubby and non-native grasslands, prairies, meadows, agricultural fields; 0–2600 m; Alta., B.C., Man., Sask.; Ariz., Calif., Colo., Idaho, Ill., Iowa, Kans., Mich., Minn., Mo., Mont., Nebr., Nev., N.Mex., N.Dak., Okla., Oreg., S.Dak., Tex., Utah, Wash., Wis., Wyo; introduced in e Europe.

Asclepias speciosa is the western counterpart of A. syriaca; both are broad-leaved species with large umbels of pinkish flowers. The distinctive, large, taper­ing corona segments, which form the broadest corona span of any American species of Asclepias, immediately distinguish A. speciosa from A. syriaca. These species hybridize extensively from Minnesota and southern Manitoba to Kansas, blurring the distinctions in the zone of contact, which corresponds roughly to the tran­sition from tallgrass to mixed-grass prairie (R. P. Adams et al. 1987b). Not every individual in this zone can be readily assigned to one species or the other. This is the most extensive hybrid zone in North American Asclepias. These hybrids have also been documented in Illinois, far to the east of the contact zone. Possible hybrids with A. eriocarpa and A. hallii in California are discussed under those species. Outside of its contig­uous range in the West, A. speciosa is known from a few sporadic, mostly historical records from Illinois, Michigan, Missouri, and Wisconsin. Most, if not all, of these records represent adventive, ephemeral outposts from the native range.