Asclepias tuberosa
Asclepias californica
asclépiade tubéreuse, butterfly milkweed
California milkweed, round-hood milkweed
1–numerous, erect to ascending, branched in inflorescence, 15–90 cm, densely hirsute, not glaucous, rhizomes absent.
1–20+, decumbent to erect, rarely branched, 15–90 cm, densely tomentose, 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, stipular colleters absent;
petiole 0–17 mm, densely tomentose;
blade ovate to lanceolate or oval, 5–18 × 2.5–10.5 cm, chartaceous, base cordate to truncate, margins often minutely erose, apex acuminate, venation eucamptodromous to faintly brochidodromous, surfaces densely tomentose to glabrate, 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 extra-axillary at upper nodes, sessile or pedunculate, 5–21-flowered;
peduncle 0–2.5 cm, densely tomentose, with 1 caducous bract at the base of each pedicel.
9–24 mm, puberulent with curved trichomes to pilosulous.
15–40 mm, densely tomentose.
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 linear to narrowly lanceolate, 4–6 mm, apex acute, densely tomentose;
corolla green or tan (sometimes tinged pink) to pinkish purple, red-violet at base, lobes reflexed with spreading tips, oval, 8–11 mm, apex acute, densely tomentose abaxially, pilose at base adaxially;
gynostegial column 2–3.5 mm;
fused anthers dark brown, columnar, 2–2.5 mm, wings right-triangular, closed, apical appendages deltoid;
corona segments red-violet, sometimes pale at apex, sessile, conduplicate, dorsally rounded, 3–6 mm, exceeded by style apex, base slightly to strongly saccate, margins connivent, apex rounded to truncate, slightly to strongly oblique, papillose, internal appendage absent;
style apex planar, green.
ovate, 8–9 × 4–5 mm, margin winged, faces minutely rugulose;
coma 3–5 cm.
broadly oval to orbiculate, 9–12 × 8–11 mm, margin very narrowly winged, faces rugulose;
coma 1.5–2.5 cm.
erect on upcurved pedicels, fusiform, 7–14 × 1.2–2 cm, apex long-acuminate or attenuate, smooth, hirsute.
sometimes paired, erect on upcurved pedicels, ovoid, 5–12.5 × 2–3 cm, apex apiculate to acuminate, longitudinally ridged, densely tomentose.
= 22.
Asclepias tuberosa
Asclepias californica
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.)
Subspecies 2 (2 in the flora).
Asclepias californica is one of the showiest milkweed species in the flora, with red-violet flowers set off by the dense, white, wooly vestiture of the rest of the plant. It is available from California nurseries but can be difficult to maintain in cultivation. An old report of the species from Baja California Sur cannot be confirmed and likely stems from a misidentification or erroneous location. Although the coronas are notoriously variable within the recognized subspecies, the key characters reliably distinguish northern and southern population systems. However, intermediates can be found in the contact zone, in Kern County.
Gomphocarpus tomentosus (Torrey) A. Gray (not Burchell 1822) is an illegitimate name found in some older regional floras that pertains here.
(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 |
1. Corona segments 4–6 mm, apex usually rounded, opening extending from apex to base more than halfway, often more than three-quarters. | subsp. californica |
1. Corona segments 3–4 mm, apex truncate or rounded, opening extending from apex to base less than, rarely up to, halfway. | subsp. greenei |
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