Asclepias syriaca
Asclepias eastwoodiana
asclépiade commune, broadleaf milkweed, common milkweed
Eastwood's milkweed
1 (rarely more, but forming dense colonies), erect, unbranched (rarely branched), 50–200 cm, tomentose to puberulent with curved trichomes, not glaucous, rhizomatous.
1–6, ascending to decumbent, unbranched or branched near base, 6–30 cm, puberulent with curved trichomes, not glaucous, rhizomatous.
opposite, petiolate, with 1–5 stipular colleters on each side of petiole;
petiole 5–15 mm, tomentose to puberulent with curved trichomes;
blade oval or ovate to oblong or elliptic, 6–30 × 2.5–11 cm, chartaceous, base cuneate to rounded or truncate, margins entire, apex obtuse to rounded or acute, often mucronate, venation brochidodromous, surfaces tomentose to pilosulous abaxially, tomentose to glabrate adaxially, margins ciliate, 4–20 laminar colleters.
proximally opposite, distally alternate, petiolate, with 0 or 1 stipular colleter on either side of petiole;
petiole 2–10 mm, puberulent with curved trichomes;
blade narrowly lanceolate to ovate, 2–4.5 × 0.6–3 cm, chartaceous, base cuneate to obtuse, margins entire, apex acute, mucronate, venation eucamptodromous, surfaces strigulose or pilosulous on midvein to glabrate, margins densely ciliate, laminar colleters absent.
extra-axillary, pedunculate, 24–113-flowered;
peduncle 2–12 cm, tomentulose to pilose or puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
terminal and extra-axillary at upper nodes, sessile or pedunculate, 2–25-flowered;
peduncle 0–4 cm, puberulent with curved trichomes to glabrate, bracts few.
17–40 mm, densely pilose to puberulent with curved trichomes.
10–28 mm, pilosulous to puberulent with curved trichomes.
erect to pendent;
calyx lobes elliptic, 3–6 mm, apex acute, tomentulose;
corolla dark to pale pink or green and pink-tinged, lobes reflexed with spreading tips, oblong to oval, 6–9 mm, apex acute, pilose abaxially, minutely hirtellous at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 2–2.5 mm, wings narrowly right-triangular, slightly open, apical appendages ovate;
corona segments reddish purple to cream, sessile, tubular, slightly flattened dorsally, 4–5 mm, exceeding style apex, apex obtuse, somewhat to strongly flared, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, green or pale to dark pink.
erect;
calyx lobes elliptic to lanceolate, 2–2.5 mm, apex acute, puberulent with curved trichomes to pilosulous;
corolla red-violet, faintly striate, lobes reflexed with spreading tips, oval, 4–5 mm, apex acute, glabrous;
gynostegial column 0.2–0.5 mm;
fused anthers brown, cylindric, 1.5–2 mm, wings right-triangular, apical appendages ovate;
corona segments red-violet dorsally, white proximally, sessile, cupulate, 1.5–2 mm, slightly exceeded by style apex, apex truncate with a proximal tooth on each side, glabrous, internal appendage conical, barely exserted from cavity, glabrous;
style apex shallowly depressed, pink to red-violet.
narrowly ovate, 7–8 × 4–5 mm, margin winged, faces rugulose;
coma 3–4 cm.
not seen.
erect on upcurved pedicels, lance-ovoid to ovoid, 7–12 × 2–4 cm, apex acuminate, smooth or muricate, tomentose.
spreading to pendulous on spreading pedicels, lance-ovoid, 3.5–6 × 0.5–1 cm, apex acuminate, smooth, faintly striate, strigose.
= 22.
Asclepias syriaca
Asclepias eastwoodiana
Asclepias syriaca is surely the most familiar milkweed in North America, and one that evokes ambivalence. It has been considered an undesirable species because of its prolific rhizomatous spread and ability to invade and thrive in cultivated land. However, it has been used as a food plant by indigenous and colonizing peoples, and its pleasantly fragrant and nectariferous flowers are avidly sought by diverse insects, highlighting the ecological importance of A. syriaca. Moreover, it has come to be appreciated because of its importance as one of the most commonly utilized host plants of the monarch butterfly, Danaus plexippus. There is some evidence that its population in agricultural lands in the upper midwestern United States has dramatically declined in the last several decades. However, its range and abundance prior to European settlement are not well understood and may have been much lower than in historical times, particularly in deforested areas of the eastern United States. It is considered to have been introduced to Newfoundland, Alabama, Georgia, Louisiana, Mississippi, and South Carolina and has been reported, but without documentation, from Texas. It has been documented from Salem, Oregon, but appears to not be established there (R. Halse, pers. comm.). It is considered to be of conservation concern at the northwesternmost edge of its range in Saskatchewan, where a single population is known in Estevan Municipality. Asclepias syriaca is the most promiscuous of milkweeds, as it is known to hybridize with at least seven other species (A. amplexicaulis, A. exaltata, A. ovalifolia, A. purpurascens, A. speciosa, A. sullivantii, A. tuberosa). Hybrids with A. speciosa are most frequent, as discussed under that species. Hybrids with A. exaltata are not infrequently encountered in the Appalachian Mountains and elsewhere. Other hybrids are highly localized. In all cases, putative hybrids are inferred from intermediate floral and vegetatative traits.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias eastwoodiana and the next three species (A. ruthiae, A. sanjuanensis, A. uncialis) form a complex of largely allopatric entities that have sometimes been united in a single species, for which the name A. uncialis holds priority (for example, E. Sundell 1994). However, each entity shows genetic, chemical, and subtle morphological distinctions, supporting recognition at the specific rank (M. B. Sady and J. N. Seibert 1991; J. P. Riser et al. 2019). Asclepias eastwoodiana is distinguished from the others by the differences in leaf shape, vestiture, and corona morphology indicated in the key. With A. ruthiae it shares a spreading to pendulous fruit that differs from the typically erect fruits of A. sanjuanensis and A. uncialis. Asclepias eastwoodiana is endemic to valleys in central Nevada (Esmeralda, Lander, Lincoln, Mineral, and Nye counties), where it is considered to be a species of conservation concern, potentially threatened by livestock trampling and mining development.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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