Asclepias arenaria |
Asclepias incarnata |
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sand milkweed |
asclépiade incarnate, rose milkweed, swamp milkweed, swamp silkweed, white Indian hemp |
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Habit | Herbs. | Herbs. | ||||
Stems | 1–8, spreading or decumbent to erect, unbranched or rarely branched near base, 20–100 cm, tomentose, not glaucous, rhizomatous. |
1–few, erect, unbranched to inflorescence, 30–150 cm, puberulent in a line with curved trichomes or densely pilose to glabrate, not glaucous, rhizomes absent. |
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Leaves | opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole plus 0–4 in axil; petiole 7–17 mm, tomentose; blade oblong or obovate to ovate or oval, 4.2–11.5 × 2.5–7.5 cm, subcoriaceous, base rounded or truncate to subcordate, margins often undulate or crisped, apex truncate to rounded (rarely acute), sometimes emarginate, often mucronate, venation brochidodromous, surfaces tomentose to nearly glabrate, margins ciliate, 12–24 laminar colleters. |
opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge; petiole 1–15 mm, pilosulous to pilose; blade lanceolate to linear-lanceolate or ovate, 5–15 × 0.5–4.5 cm, membranous, base obtuse to rounded or subcordate, margins entire, apex acute to acuminate or attenuate, venation eucamptodromous, surfaces sparsely puberulent with curved trichomes or pilose to glabrate, margins ciliate, 2–6 laminar colleters. |
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Inflorescences | extra-axillary (sometimes appearing terminal), sessile or pedunculate, 14–51-flowered; peduncle 0–2 cm, tomentose, with 1 caducous bract at the base of each pedicel. |
extra-axillary at upper nodes, branched, pedunculate, 10–31-flowered; peduncle 1.5–7 cm, puberulent with curved trichomes to pilosulous, sometimes only on 1 side, to pilose, with 1 caducous bract at the base of each pedicel. |
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Pedicels | 15–25 mm, densely tomentose. |
10–15 mm, pilosulous to puberulent with curved trichomes, sometimes only on 1 side, to pilose. |
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Flowers | erect to pendent; calyx lobes lanceolate, 2.5–3 mm, apex acute, densely tomentose; corolla green to yellowish green, sometimes tinged reddish or purplish, lobes reflexed with spreading tips, oval, 7–8 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially; gynostegial column 1–2 mm; fused anthers green, obconic, 2–2.5 mm, wings right-triangular, closed, apical appendages ovate; corona segments cream to greenish cream or ochroleucous, subsessile, conduplicate, flaring at base, 3.5–4 mm, exceeding style apex, apex truncate to rounded, emarginate, minutely papillate, proximal margin toothed, internal appendage falcate, exserted, sharply incurved over style apex, apex upturned, minutely papillose. |
erect; calyx lobes lanceolate, 2–2.5 mm, apex acute, pilosulous to puberulent with curved trichomes; corolla pink to white, lobes reflexed with spreading tips, elliptic, (4.5–)5–6 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially; gynostegial column 1.2–1.5 mm; fused anthers green to brown, columnar, 1.5–2 mm, wings narrowly right-triangular, slightly open at base, apical appendages deltoid; corona segments pink to white, often paler than corolla, stipitate, tubular, dorsally rounded to slightly flattened, 2–2.5 mm, ± equaling style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous; style apex shallowly depressed, green, white, or pink. |
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Seeds | oval, 9–12 × 6–8 mm, margin winged, faces minutely rugulose; coma 2–3 cm. |
ovate, 8–9 × 5–6 mm, margin broadly winged, faces smooth; coma 1.5–2 cm. |
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Follicles | erect on upcurved pedicels, lance-ovoid, 5.5–10 × 2–2.8 cm, apex acuminate, smooth, pilosulous. |
erect on straight pedicels, fusiform, 6–9 × 0.8–1.2 cm, apex long-acuminate, smooth to indistinctly ribbed, sparsely puberulent with curved trichomes to pilose or pilosulous. |
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Asclepias arenaria |
Asclepias incarnata |
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Phenology | Flowering May–Aug(–Oct); fruiting Jul–Sep(–Oct). | |||||
Habitat | Sandhills, dunes, sandy soils, prairies, pastures, grasslands, oak scrub, riparian areas. | |||||
Elevation | 100–1900 m. (300–6200 ft.) | |||||
Distribution |
CO; KS; NE; NM; OK; SD; TX; WY; Mexico (Chihuahua)
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North America; n Mexico
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Discussion | Asclepias arenaria is the milkweed most consistently associated with pure sand soils in the western Great Plains. It is predictably found at the bases of stabilized and semi-stabilized dunes. Flowers of this species are visited by a variety of Hymenoptera, notably several species of large wasps, including tarantula hawk wasps (Pepsinae, Pompilidae) and scoliid wasps (Scoliidae), as well as by Lepidoptera. Non-flowering shoots of A. arenaria may produce linear leaves; they are easily overlooked and not identified as belonging to this species unless one is aware of this variation, especially when they are produced on rhizomes distant from shoots with typical foliage. This trait is found in several other broad-leaved milkweeds (for example, A. erosa, A. welshii). Asclepias arenaria is rare and considered to be of conservation concern in Wyoming, where it has been recorded from only two sites in Goshen County. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Subspecies 2 (2 in the flora). Asclepias incarnata can be grown in a great variety of soil types and is surprisingly drought tolerant considering its natural predilection for hydric and mesic soils. As an easily grown, attractive, versatile species, it is one of the best options for gardening with milkweeds. It consists of two morphologically and geographically distinct, but intergrading subspecies. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 14. | FNA vol. 14. | ||||
Parent taxa | Apocynaceae > Asclepias | Apocynaceae > Asclepias | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Name authority | Torrey in W. H. Emory: Rep. U.S. Mex. Bound. 2(1): 162. (1859) | Linnaeus: Sp. Pl. 1: 215. (1753) | ||||
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