Asclepias obovata
Asclepias arenaria
pineland milkweed
sand milkweed
1 (rarely more), erect to spreading, unbranched, 40–70(–200) cm, densely hirtellous to velutinous, not glaucous, rhizomes absent.
1–8, spreading or decumbent to erect, unbranched or rarely branched near base, 20–100 cm, tomentose, not glaucous, rhizomatous.
opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 1–4 mm, densely hirtellous to velutinous;
blade oblong or elliptic to obovate or ovate, 4–9 × 1–3.5 cm, subcoriaceous, base rounded or truncate to cordate, margins sometimes crisped, apex acute to truncate, sometimes emarginate, often mucronate, venation brochidodromous, surfaces densely hirtellous to velutinous abaxially, hirtellous adaxially, margins ciliate, 8–12 laminar colleters.
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.
extra-axillary, sometimes also appearing terminal, sessile or pedunculate, 7–31-flowered;
peduncle 0–0.5 cm, densely hirtellous to velutinous, with 1 caducous bract at the base of each pedicel.
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.
10–12 mm, densely hirtellous to velutinous.
15–25 mm, densely tomentose.
erect to pendent;
calyx lobes elliptic, 5–6 mm, apex acute, densely hirtellous;
corolla green, sometimes tinged reddish or bronze, lobes reflexed, sometimes with spreading tips, elliptic, 7–9 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, obconic, 2.5–4 mm, wings right-triangular, open at base, apical appendages broadly ovate;
corona segments bronze to yellow, often tinged red, sometimes apically cream or pale, stipitate, tubular, somewhat flattened laterally, flared at base, 5–8 mm, greatly exceeding style apex, apex rounded, flared, glabrous, internal appendage falcate, exserted, sharply incurved over style apex, glabrous;
style apex shallowly depressed, green.
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.
broadly ovate, 8–9 × 6–7 mm, margin winged, faces smooth;
coma 2–5 cm.
oval, 9–12 × 6–8 mm, margin winged, faces minutely rugulose;
coma 2–3 cm.
erect on upcurved pedicels, narrowly to broadly fusiform, 7.5–12.5 × 1.5–2.5 cm, apex acuminate, smooth, densely hirtellous to velutinous.
erect on upcurved pedicels, lance-ovoid, 5.5–10 × 2–2.8 cm, apex acuminate, smooth, pilosulous.
Asclepias obovata
Asclepias arenaria
Asclepias obovata is a common milkweed of seasonally wet, sandy soils in pine woodlands of the Gulf Coastal Plain and (rarely) the southern Atlantic Coastal Plain. It is rare and considered to be of conservation concern in Arkansas.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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