Asclepias obovata
Asclepias rusbyi
pineland milkweed
Rusby's milkweed
1 (rarely more), erect to spreading, unbranched, 40–70(–200) cm, densely hirtellous to velutinous, not glaucous, rhizomes absent.
1 or 2 (rarely more), erect, sometimes branched, 50–100 cm, glabrous, not glaucous, rhizomes absent.
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.
alternate, sessile or petiolate, drooping, with 1 stipular colleter on each side of petiole;
petiole 0–0.1 cm, glabrous;
blade linear, conduplicate, 9–15 × 0.2–0.3 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly brochidodromous to obscure, surfaces glabrous, margins ciliate, laminar colleters absent.
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, sessile or pedunculate, 7–28-flowered;
peduncle occasionally branched, 0–1.5 cm, pilosulous, with 1 caducous bract at the base of each pedicel.
10–12 mm, densely hirtellous to velutinous.
7–10 mm, pilose.
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 spreading;
calyx lobes narrowly lanceolate, 3–4 mm, apex acute, pilosulous to glabrate;
corollas abaxially russet or tan or bronze to pale green, adaxially pale green, lobes reflexed with ascending tips, elliptic, 4–6 mm, apex acute, glabrous;
gynostegial column 0–0.5 mm;
fused anthers green, obconic, 3 mm, wings crescent-shaped, connivent distally, wider and open at base, apical appendages deltoid, obscuring corpuscula;
corona segments yellowish green to yellow or bronze, sessile, chute-shaped, 1.5–2.5 mm, exceeded by style apex, base saccate, auriculate, apex truncate, glabrous;
internal appendage absent or a low crest, glabrous;
style apex shallowly depressed, green to yellowish green.
broadly ovate, 8–9 × 6–7 mm, margin winged, faces smooth;
coma 2–5 cm.
ovate, 6–8 × 4–6 mm, margins winged, faces minutely papillose and rugulose;
coma 2–2.5 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, 9–12.5 × 1.5–2.5 cm, apex long-acuminate, smooth, faintly striate, sparsely pilosulous to glabrate.
Asclepias obovata
Asclepias rusbyi
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.)
As noted under Asclepias engelmanniana, A. rusbyi has been only inconsistently recognized as distinct from its more widespread relative. The species has an unusual distribution. In the north, A. rusbyi is encountered on the Colorado Plateau north of the Colorado River and extends west into pinyon-juniper woodlands and desert canyons at the upper margin of the Sonoran Desert. A few populations have been documented in Colorado (Archuleta, La Plata, Mesa, Montezuma, and Montrose counties), Nevada (Lincoln County), northern New Mexico (Rio Arriba and San Juan counties), and Utah (Garfield, San Juan, and Washington counties), and should be considered to be of conservation concern in these states. South of the Colorado River, A. rusbyi is found throughout eastern Arizona, from the southern edge of the Colorado Plateau, through the Mogollon Rim, to the sky-island mountains of the border region, where it is found in pinyon-juniper woodlands and pine-oak forests. In this region, it is rare in New Mexico (Catron and Grant counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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