Asclepias syriaca
Asclepias texana
asclépiade commune, broadleaf milkweed, common milkweed
Texas 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–numerous, erect, sparsely to moderately branched in upper half, 25–90 cm, puberulent with curved trichomes in a line, 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, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 5–20 mm, puberulent with curved trichomes;
blade ovate to lanceolate or elliptic, 2–7 × 0.5–3 cm, chartaceous, base cuneate to obtuse, margins entire, apex acute to acuminate, venation eucamptodromous, surfaces puberulent with curved trichomes on veins abaxially, sparsely puberulent with curved trichomes on veins to glabrate adaxially, 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.
extra-axillary at upper nodes, some appearing terminal, pedunculate, 14–31-flowered;
peduncle 0.9–3 cm, puberulent with curved trichomes in a line, with 1 caducous bract at the base of each pedicel.
17–40 mm, densely pilose to puberulent with curved trichomes.
7–14 mm, puberulent with curved trichomes in a line.
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 narrowly lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes;
corolla white, sometimes tinged green, lobes reflexed with spreading tips, elliptic, 3.5–5 mm, apex acute to obtuse, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers brown, columnar, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments white, sometimes tinged pink, stipitate, cupulate, dorsally rounded, 2–3 mm, equaling to slightly exceeding style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;
style apex shallowly depressed, white.
narrowly ovate, 7–8 × 4–5 mm, margin winged, faces rugulose;
coma 3–4 cm.
ovate, 6–7 × 4–5 mm, margin winged, faces smooth or sparsely papillose;
coma 2–3 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, 9–13 × 0.5–1 cm, apex long-acuminate to attenuate, smooth, glabrous.
= 22.
Asclepias syriaca
Asclepias texana
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.)
In the flora area, Asclepias texana has a disjunct distribution on the Edwards Plateau and in the mountains of the Big Bend region. Although commonly occurring in canyons and riparian areas, A. texana is quite drought tolerant in cultivation. The tidy, bushy habit, long flowering stems topped by bright white spherical umbels, and rapid growth from seed make this a suitable candidate for horticultural use. It is known to be hardy to at least USDA Zone 7.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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