Asclepias tuberosa
Asclepias scaposa
asclépiade tubéreuse, butterfly milkweed
bear mountain milkweed
1–numerous, erect to ascending, branched in inflorescence, 15–90 cm, densely hirsute, not glaucous, rhizomes absent.
1–5+, erect, unbranched (rarely at base), 15–20 cm, pilosulous, 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, sessile or petiolate, with 1 stipular colleter on each side of petiole;
petiole 0–6 mm, pilosulous to glabrate;
blade oval to elliptic, 6–8 × 1.5–2.5 cm, membranous, base cuneate, margins crisped, apex obtuse to acute, venation eucamptodromous, surfaces sparsely hirtellous, 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, solitary, pedunculate, 15–30-flowered;
peduncle 7–17 cm, pilose, bracts absent or few.
9–24 mm, puberulent with curved trichomes to pilosulous.
15–20 mm, pilose.
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.
erect to pendent;
calyx lobes narrowly lanceolate, 2–2.5 mm, apex acute, pilose;
corolla green with purplish tinge (reddish purple), lobes reflexed, elliptic, 4–5 mm, apex acute, glabrous;
gynostegial column 0.5–1 mm;
fused anthers brown, cylindric, 1.5–2 mm, wings curved, wider at base, apical appendages ovate;
corona segments cream, sometimes yellow- or red-tinged or yellow or red at base, sessile, tubular, 2–3 mm, exceeding style apex, base saccate, apex truncate, dentate, glabrous, internal appendage falcate, exserted, arching above style apex, glabrous;
style apex shallowly depressed, green or cream.
ovate, 8–9 × 4–5 mm, margin winged, faces minutely rugulose;
coma 3–5 cm.
not seen.
erect on upcurved pedicels, fusiform, 7–14 × 1.2–2 cm, apex long-acuminate or attenuate, smooth, hirsute.
erect on upcurved pedicels, fusiform, 5–6 × 1–1.5 cm, apex long-acuminate, smooth, pilosulous.
= 22.
Asclepias tuberosa
Asclepias scaposa
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.)
The long-pedunculate, terminal inflorescence combined with short stature is distinctive in Asclepias scaposa. Although the locality of one of the syntypes was attributed to New Mexico by E. L. Greene, that is the only report for that state. Both syntypes were collected by Charles Wright for the United States-Mexico boundary survey, but neither of his labels indicates that they were collected in New Mexico. It is very likely that both collections were made in Texas or northeastern Mexico, and New Mexico is excluded from the distribution here. The common name Bear Mountain milkweed may refer to a ridge in the northwestern portion of the Davis Mountains, although no collections are known from this area. The few collections and observations that have been made in Texas are from scattered locations in Brewster, Crockett, Pecos, Presidio, Reeves, and Terrell counties, and conservation status in the United States merits assessment. In Mexico, A. scaposa also has been rarely collected, except for a local area in Nuevo León (Municipio de Galeana).
(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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