Asclepias syriaca
Asclepias quadrifolia
asclépiade commune, broadleaf milkweed, common milkweed
asclépiade à quatre feuilles, four-leaf 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, erect, unbranched, 25–60 cm, puberulent on 1 side with curved trichomes to glabrate, not glaucous, rhizomes absent.
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.
opposite, 2 mid-stem pairs usually with shortened internode forming a pseudo-whorl, petiolate, with 1 stipular colleter on each side of petiole;
petiole 2–7 mm, puberulent with curved trichomes;
blade ovate to elliptic, 2.5–12 × 1–6 cm, membranous, base cuneate, margins entire, apex acute to attenuate or acuminate, venation eucamptodromous, surfaces inconspicuously puberulent on veins with curved trichomes, margins 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, sometimes branched, and usually also extra-axillary at upper nodes, sessile or pedunculate, 7–31-flowered;
peduncle 0–3.5 cm, puberulent on 1 side with curved trichomes, with 1 caducous bract at the base of each pedicel.
17–40 mm, densely pilose to puberulent with curved trichomes.
17–28 mm, puberulent on 1 side 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.
spreading to pendent;
calyx lobes lanceolate, 1.5–2 mm, apex acute, glabrous;
corolla pink or cream, lobes reflexed, elliptic, 4–5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 0.5–1.5 mm;
fused anthers tan to brown, cylindric, 1–1.5 mm, wings right-triangular, closed, apical appendages ovate;
corona segments pink or cream, sometimes striped pink dorsally, sessile, conduplicate, flattened dorsally, 2.5–4 mm, exceeding style apex, apex obtuse, oblique, glabrous, internal appendage subulate, exserted, arched to sharply inflexed over style apex, glabrous;
style apex shallowly depressed, cream to pale pink.
narrowly ovate, 7–8 × 4–5 mm, margin winged, faces rugulose;
coma 3–4 cm.
ovate, 6–7 × 4–5 mm, margin winged, faces rugulose;
coma 3–4.5 cm.
erect on upcurved pedicels, lance-ovoid to ovoid, 7–12 × 2–4 cm, apex acuminate, smooth or muricate, tomentose.
erect on straight pedicels, narrowly fusiform, 8–16 × 0.4–1 cm, apex long-attenuate, smooth, sparsely puberulent with curved trichomes to glabrate.
= 22.
Asclepias syriaca
Asclepias quadrifolia
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 quadrifolia is small statured compared to the other deciduous forest milkweeds. It is found predominantly on slopes of eroded, sedimentary rocks, especially cherty limestone. Like A. purpurascens, it is distributed primarily in the Appalachian and Ozark mountains. Populations with pinkish flowers are lovely in early spring; other populations have a more washed-out coloration. The characteristic pseudo-whorl of four mid-stem leaves is not always present. Like other forest milkweeds, it has experienced large population reductions at the northeastern margin of its range due to habitat loss. It is considered to be extirpated from Delaware and to be rare and of conservation concern in New Hampshire, Rhode Island (Providence County), and Ontario (Prince Edward County), as well as to the west in Kansas (Cherokee County). It has been reported, but not verified, from Minnesota. Putative hybrids with A. exaltata have been documented very rarely from the Appalachian Mountains and can be recognized by intermediate floral and vegetative traits.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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