Asclepias viridiflora

Herbs. Stems solitary, erect to ascending, unbranched (rarely), (10–)20–125 cm, puberulent with curved trichomes, not glau­cous, rhizomes absent. Leaves opposite to subopposite, sessile or petiolate, with 1 or 2 stipular colleters on each side of petiole and also in axil; petiole 0–5 mm, puberulent with curved trichomes; blade linear to broadly oval or nearly orbiculate, 2–13 × 0.8–6 cm, chartaceous, base cuneate to rounded, margins entire or crisped, apex acute or obtuse to truncate or emarginate, mucronate, venation brochidodromous, surfaces sparsely pilosulous to glabrate, margins ciliate, laminar colleters absent. Inflorescences extra-axillary at upper nodes, sometimes branched at peduncle apex, sessile or pedunculate, 22–60-flowered; peduncle 0–4 cm, puberulent with curved trichomes to pilosulous, with 1 caducous bract at the base of each pedicel. Pedicels 7–13 mm, pilosulous. Flowers erect to pendent; calyx lobes narrowly lanceolate, 2–3 mm, apex acute, pilosulous; corolla green to yellowish green, sometimes tinged red, lobes reflexed, oblong, 5–7 mm, apex acute, inconspicuously pilosulous at apex abaxially, glabrous adaxially; gynostegium sessile; fused anthers green, cylindric, 3–4 mm, wings triangular, widest at middle, closed, apical appendages ovate, marginally inflexed, apically deflexed; corona segments green to cream, sometimes tinged red, sessile, laminar, margins incurved, appressed to column, 3–4 mm, greatly exceeded by style apex, apex obtuse, glabrous, internal appendage absent or obscure, glabrous; style apex shallowly depressed, green. Follicles erect on upcurved pedicels, fusiform to lance-ovoid, 6–10 × 1.5–2 cm, apex acuminate to attenuate, smooth, pilosulous. Seeds ovate, 7–8 × 4–5 mm, margin winged, faces minutely rugulose; coma 2.5–3 cm. 2n = 22.

Phenology: Flowering Apr–Sep(–Oct); fruiting Jun–Nov.
Habitat: Slopes, ridges, bluffs, flats, canyons, arroyos, glades, fields, meadows, pastures, sandhills, dunes, pond edges, streamsides, playas, sandstone, limestone, gypsum, ser­pentine, dolomite, alluvium, silty, sandy, clay, rocky, and calcareous soils, prairies, desert grasslands, oak scrub, oak, oak-juniper, oak-hickory, pine-oak, and pine woodlands, forest openings and edges.
Elevation: 0–2300 m.

Distribution

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Alta., Man., Ont., Sask., Ala., Ariz., Ark., Colo., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mich., Minn., Miss., Mo., Mont., Nebr., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis., Wyo., Mexico (Coahuila).

Discussion

Asclepias viridiflora is one of the milkweeds with spherical, greenish umbels and inconspicuous coronas (see also A. engelmanniana, A. hirtella, A. lanuginosa, A. longifolia, A. rusbyi, A. stenophylla). Prior to close examination, the tight green balls of open flowers appear to be merely in bud. The diversity in leaf morphology among individuals (linear to orbiculate) is remarkable, but has no taxonomic significance—the full range of variation may be found within single populations. This is the most widespread milkweed within the flora area, ranging across most of the United States (absent only from the westernmost states and most of New England) and southern Canada. It is nowhere abundant, but may be regularly encountered in suitable, thin-soiled prairie habitats, especially in the Great Plains. It is rare and considered to be of conservation concern on the margins of its range, in Alberta (Cypress, Forty Mile, and Warner counties), Arizona (Coconino, Gila, and Yavapai counties), Connecticut (New Haven County), Florida (Gadsden and Jackson counties), and New York (Columbia, Nassau, Richmond, and Suffolk counties).

Selected References

None.

Lower Taxa

None.