Asclepias erosa
Asclepias perennis
desert milkweed
aquatic milkweed, aquatic or white swamp or swamp or thin-leaf milkweed
1–12, erect to decumbent, unbranched, 40–250 cm, thinly tomentose to glabrate, not glaucous, rhizomatous.
1–5, erect, sparsely to moderately branched, especially towards base, 30–60 cm, puberulent with curved trichomes in a line to glabrate, not glaucous, rhizomatous.
opposite, sessile or petiolate, with 0 or 1 stipular colleter on each side of petiole;
petiole 0–6 mm, thinly tomentose to glabrate;
blade ovate to lanceolate, 7.5–25 × 2.5–15 cm, succulent, base truncate to cordate, margins minutely erose, apex attenuate to acuminate, venation eucamptodromous, surfaces tomentose to glabrate, margins ciliate, minutely erose, laminar colleters absent.
persistent or gradually caducous from the base, opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 10–12 mm, ciliate;
blade narrowly elliptic to oval or oblong, 5–14 × 0.3–3 cm, membranous or chartaceous, base cuneate, margins entire, apex acute to attenuate or acuminate, minutely mucronate, venation faintly brochidodromous to eucamptodromous, surfaces sparsely puberulent with curved trichomes, more densely on veins, to glabrate, margins inconspicuously ciliate, laminar colleters absent.
terminal and extra-axillary, sometimes branched, pedunculate, 12–50-flowered;
peduncle 2–10 cm, tomentose, with 1 caducous bract at the base of each pedicel.
extra-axillary at upper nodes, sometimes appearing terminal, pedunculate, 12–30-flowered;
peduncle 1.5–5 cm, puberulent with curved trichomes, sometimes only on 1 side, with 1 caducous bract at the base of each pedicel.
20–45 mm, densely tomentose to glabrate.
7–13 mm, puberulent with curved trichomes, sometimes only on 1 side.
erect to pendent;
calyx lobes lanceolate, 4–5 mm, apex acute, tomentose to glabrate;
corolla green, lobes reflexed, tips sometimes spreading, oval, 6–9 mm, apex acute, tomentose towards tips abaxially, glabrous adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 2.5–3 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream to ochroleucous, stipitate, conduplicate, dorsally rounded, 3–5.5 mm, slightly exceeding style apex, apex truncate with a proximal tooth on each side, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, cream to greenish cream.
erect to spreading;
calyx lobes narrowly lanceolate to linear, 1.2–1.5 mm, apex acute, puberulent with curved trichomes;
corolla white to pink-tinged, lobes reflexed with spreading tips, elliptic, 3–4 mm, apex acute to obtuse, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 0.8–1.2 mm;
fused anthers brown, cylindric, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments white, sometimes faintly pink-tinged, stipitate, tubular, dorsally rounded, 1.5–2.5 mm, slightly exceeding style apex, apex obtuse to acute, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;
style apex shallowly depressed, white, sometimes pink-tinged.
ovate, 8–13 × 5–10 mm, margin narrowly winged, faces minutely rugulose, ridges papillose;
coma 2–2.5 cm.
broadly oval, 12–15 × 11–14 mm, margin broadly winged, faces smooth;
coma absent.
erect on upcurved pedicels, lance-ovoid to ovoid, 6.5–10 × 2–3.5 cm, apex acuminate to apiculate, smooth, thinly tomentose.
pendulous on declined pedicels, lance-ovoid, 4–7 × 1–2.5 cm, apex long-acuminate, smooth, glabrous.
= 22.
Asclepias erosa
Asclepias perennis
Asclepias erosa is one of the most remarkable milkweeds. It inhabits the driest regions in the flora area, yet it is one of the tallest and largest-leaved species of Asclepias. Its leaves attain a greater size than any other sympatric milkweed, and it may possess the largest leaves of any co-occurring vascular plant species in its range. It is found most commonly in desert arroyos, and it is assumed to be deep rooted and to access reliable sources of water, which would explain its anomalously large size. Like several other milkweeds inhabiting the American deserts, A. erosa has white coronas and is commonly visited by tarantula hawk wasps (Pompilidae, Pepsinae). It is considered rare in Utah, where it enters the state only in Washington County. Asclepias erosa is often confused with A. eriocarpa, another robust species with an overlapping range in southern California. Asclepias erosa has strictly opposite, sessile to shortly petiolate leaves with erose margins and corona segments that are level at the apex and only rarely pinkish, whereas A. eriocarpa has leaves that may be opposite, alternate, or whorled, with longer petioles, and entire margins, and corona segments with oblique apices and that are often pinkish.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias perennis is the most hydrophytic North American milkweed and is often found emerging from standing water in swamps and ditches. The pendulous fruits and hairless seeds are distinctive; it is the only milkweed in the United States with seeds lacking a coma, and only one of three such species in North America. It is widely distributed along the coastal plain; inland (Arkansas, Illinois, Indiana, Kentucky, Missouri, Tennessee), it is restricted to the valleys of the Mississippi and Ohio rivers and their tributaries.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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