Asclepias tuberosa
Asclepias quadrifolia
asclépiade tubéreuse, butterfly milkweed
asclépiade à quatre feuilles, four-leaf milkweed
1–numerous, erect to ascending, branched in inflorescence, 15–90 cm, densely hirsute, not glaucous, rhizomes absent.
1, erect, unbranched, 25–60 cm, puberulent on 1 side with curved trichomes to glabrate, not glaucous, rhizomes absent.
alternate, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 1–4 mm, densely hirsute;
blade elliptic, oblong, or oblanceolate to lanceolate or linear, 2–12 × 0.3–3 cm, chartaceous, base cuneate or obtuse to rounded, truncate, hastate, or cordate, margins entire, apex acute to attenuate or obtuse to rounded, venation brochidodromous to eucamptodromous, surfaces hirsute, more densely so on midvein abaxially, margins ciliate, 0–4 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.
corymbs of extra-axillary umbels on branches, sessile or pedunculate, 5–27-flowered;
peduncle 0–4 cm, sometimes branched, hirsute, 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.
9–24 mm, puberulent with curved trichomes to pilosulous.
17–28 mm, puberulent on 1 side with curved trichomes.
erect;
calyx lobes narrowly lanceolate, 2–3 mm, apex acute, hirsute to puberulent with curved trichomes;
corolla reddish orange (nearly red) to orange or yellow, lobes reflexed with spreading tips, narrowly elliptic, (5–)6–8 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1.2–1.5 mm, fused anthers yellow to yellowish green, cylindric, 2–3 mm, wings right-triangular, closed, apical appendages ovate;
corona segments reddish orange (nearly red) to orange or yellow, substipitate, conduplicate, dorsally flattened, sulcate, 5.5–7 mm, greatly exceeding style apex, apex acute, glabrous, internal appendage subulate, exserted, arching above style apex, glabrous;
style apex shallowly depressed, yellow to yellowish green.
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.
ovate, 8–9 × 4–5 mm, margin winged, faces minutely rugulose;
coma 3–5 cm.
ovate, 6–7 × 4–5 mm, margin winged, faces rugulose;
coma 3–4.5 cm.
erect on upcurved pedicels, fusiform, 7–14 × 1.2–2 cm, apex long-acuminate or attenuate, smooth, hirsute.
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 tuberosa
Asclepias quadrifolia
Subspecies 3 (3 in the flora).
Asclepias tuberosa is one of the most familiar and beloved North American milkweeds and is a favored element of pollinator gardens because of the cheery orange flowers that attract abundant insect visitors. The clear latex is unusual in the genus and is often commented upon by collectors. The subspecies of A. tuberosa are highly intergrading. It is often difficult to satisfactorily place a given specimen in a particular subspecies; however, the great majority are readily assigned. It appears that the conspicuous variation in leaf morphology across the subspecies corresponds to genetically structured population variation (R. E. Woodson Jr. 1947). However, it is unknown to what extent cultivation and other human activities have blurred the distinctions among the geographic variants. Future recognition of the subspecies should be supported by genetic study with modern techniques. Although yellow-flowered plants predominate in the western plains, color variation is often pronounced in single populations, and yellow flowers may be encountered anywhere in the range. Hybridization with A. syriaca is documented, but is exceedingly rare. Presumed hybrids can be recognized by intermediate floral and vegetative 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.)
1. Leaf bases hastate, blade margins crisped. | subsp. rolfsii |
1. Leaf bases cuneate, obtuse, rounded, truncate, or subcordate, blade margins planar. | → 2 |
2. Leaf bases cuneate to obtuse, rounded, or subcordate, apices rounded to acute, mostly east of the crest of the Appalachian Mountains. | subsp. tuberosa |
2. Leaf bases truncate or obtuse to cordate, apices acute to attenuate, mostly west of the crest of the Appalachian Mountains. | subsp. interior |
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