Curtiss’s milkweed

Oxypteryx curtissii (A. Gray) Small

Herbs. Stems 1, erect, often purplish, sometimes branched in inflorescence, 15–100 cm, puber­ulent with curved tri­chomes, not glaucous, rhizomes absent. Leaves opposite, petio­late, with 1 or 2 stipular colleters on each side of petiole; petiole 4–7 mm, puberulent with curved trichomes; blade oblong, elliptic, or oval to obovate, oblanceolate, ovate, or lanceolate, 1.8–5 × 0.5–2.5 cm, chartaceous, base obtuse to cuneate or rounded, margins entire, apex truncate to emarginate or acute, mucronate, venation brochidodromous to eucamptodromous, sur­faces sparsely puberulent on midvein with curved tric­homes, margins inconspicuously ciliate to glabrate, 2–6 laminar colleters. Inflorescences terminal and extra-axillary at upper nodes, sessile or pedunculate, 15–45-flowered; peduncle 0–4 cm, puberulent on 1 side with curved trichomes, with 1 caducous bract at the base of each pedicel. Pedicels 10–14 mm, sparsely puberulent with curved trichomes. Flowers erect; calyx lobes lance­olate, 2–3 mm, apex acute, glabrous; corolla green with bronze or purplish tinge, lobes reflexed with spreading tips, elliptic, 4–5 mm, apex acute, glabrous; gynostegial column 0.5–1 mm; fused anthers green, obconic, 1–1.5 mm, wings broadly triangular, widest at middle, closed, apical appendages ovate; corona segments white with a green and/or purple dorsal midline, sessile, conduplicate and dorsally flattened, 5–6 mm, greatly exceeding style apex, apex attenuate, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, gla­brous; style apex shallowly depressed, green to cream. Follicles erect on upcurved pedicels, fusiform, 8–10.5 × 0.8–1.5 cm, apex long-acuminate, smooth, puberulent with curved trichomes. Seeds ovate, 8–9 × 5–6 mm, margin winged, erose, faces sparsely papillose; coma 3.5–4 cm.

Flowering Apr–Oct; fruiting Jul–Oct. Low ridges, sandy soils, oak-palmetto sand scrub, pinelands; 0–50 m; Fla.

Asclepias curtissii is endemic to white-sand substrates at interior and coastal sites on the Florida peninsula. Although the species is not considered to face imminent threat of extirpation, the scrub habitats in which it is found have been, and continue to be, heavily impacted by development. Asclepias curtissii cannot be mistaken for any other milkweed in its range when in flower; however, it occurs in the same habitats as A. tomentosa, and these species overlap considerably in vegetative features. The leaves of A. curtissii can be distinguished from those of A. tomentosa by trichomes limited to the midvein (versus sparsely to densely puberulent or tomentulose throughout).