Asclepias fascicularis
Asclepias rusbyi
Mexican whorled milkweed, narrow-leaf milkweed, narrow-leaf or Mexican or Mexican whorled milkweed
Rusby's milkweed
few–numerous, erect, sparsely to moderately branched, 50–150 cm, glabrous, not glaucous, rhizomes absent.
1 or 2 (rarely more), erect, sometimes branched, 50–100 cm, glabrous, not glaucous, rhizomes absent.
3–5-whorled, sessile or petiolate, with 1–3 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 0–4 mm, margins puberulent with curved trichomes;
blade linear to linear-lanceolate or narrowly elliptic, often somewhat conduplicate, 4.5–13 × 0.2–1.8 cm, membranous, base cuneate, margins entire, apex acute or attenuate to obtuse, mucronate, venation obscure to faintly eucamptodromous, surfaces glabrous, margins eciliate, laminar colleters absent.
alternate, sessile or petiolate, drooping, with 1 stipular colleter on each side of petiole;
petiole 0–0.1 cm, glabrous;
blade linear, conduplicate, 9–15 × 0.2–0.3 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly brochidodromous to obscure, surfaces glabrous, margins ciliate, laminar colleters absent.
terminal and extra-axillary at upper nodes, sometimes branched, pedunculate, 10–37-flowered;
peduncle 0.4–5.5 cm, puberulent with curved trichomes in a line to glabrate, with 1 caducous bract at the base of each pedicel.
extra-axillary, sessile or pedunculate, 7–28-flowered;
peduncle occasionally branched, 0–1.5 cm, pilosulous, with 1 caducous bract at the base of each pedicel.
9–14 mm, puberulent with curved trichomes to pilosulous.
7–10 mm, pilose.
erect;
calyx lobes lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes to pilosulous;
corolla pale to dark pink, rarely pale green with a pink tinge, lobes reflexed with spreading tips, oval, 3–5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments cream, often tinged or striped pink, stipitate, cupulate, dorsally somewhat flattened, 1.5–2 mm, exceeded by style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching towards style apex, glabrous;
style apex shallowly depressed, cream.
erect to spreading;
calyx lobes narrowly lanceolate, 3–4 mm, apex acute, pilosulous to glabrate;
corollas abaxially russet or tan or bronze to pale green, adaxially pale green, lobes reflexed with ascending tips, elliptic, 4–6 mm, apex acute, glabrous;
gynostegial column 0–0.5 mm;
fused anthers green, obconic, 3 mm, wings crescent-shaped, connivent distally, wider and open at base, apical appendages deltoid, obscuring corpuscula;
corona segments yellowish green to yellow or bronze, sessile, chute-shaped, 1.5–2.5 mm, exceeded by style apex, base saccate, auriculate, apex truncate, glabrous;
internal appendage absent or a low crest, glabrous;
style apex shallowly depressed, green to yellowish green.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 6–8 × 4–6 mm, margins winged, faces minutely papillose and rugulose;
coma 2–2.5 cm.
erect on straight pedicels, fusiform, 6–9 × 0.5–1 cm, apex attenuate, smooth, glabrous.
erect on upcurved pedicels, lance-ovoid, 9–12.5 × 1.5–2.5 cm, apex long-acuminate, smooth, faintly striate, sparsely pilosulous to glabrate.
= 22.
Asclepias fascicularis
Asclepias rusbyi
Asclepias mexicana Decaisne was misapplied to A. fascicularis in the past; this is the legitimate name of a related species endemic to southern and eastern Mexico. The common name Mexican (whorled) milkweed stems from this past confusion. Compared to its close relatives A. angustifolia, A. linearis, A. pumila, A. subverticillata, and A. verticillata, the leaves of A. fascicularis are not particularly narrow (despite the implication of another common name). However, very narrow leaves are found in A. fascicularis when it is growing at relatively dry sites, especially at the eastern limit of its range in southeastern Idaho. Such specimens (for example, Mumford 272 [MO], Atwood 28495 [NY]) have been attributed in the past to A. subverticillata in error. Asclepias fascicularis is completely allopatric with its Incarnatae clade relatives (species 7–16). Like these species, it is easily cultivated, and its seeds are widely available. In Washington, the range of A. fascicularis is restricted largely to the valleys of the Columbia and Spokane rivers and in Idaho to the Snake and Weiser rivers.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
As noted under Asclepias engelmanniana, A. rusbyi has been only inconsistently recognized as distinct from its more widespread relative. The species has an unusual distribution. In the north, A. rusbyi is encountered on the Colorado Plateau north of the Colorado River and extends west into pinyon-juniper woodlands and desert canyons at the upper margin of the Sonoran Desert. A few populations have been documented in Colorado (Archuleta, La Plata, Mesa, Montezuma, and Montrose counties), Nevada (Lincoln County), northern New Mexico (Rio Arriba and San Juan counties), and Utah (Garfield, San Juan, and Washington counties), and should be considered to be of conservation concern in these states. South of the Colorado River, A. rusbyi is found throughout eastern Arizona, from the southern edge of the Colorado Plateau, through the Mogollon Rim, to the sky-island mountains of the border region, where it is found in pinyon-juniper woodlands and pine-oak forests. In this region, it is rare in New Mexico (Catron and Grant counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
CA
OR
WA
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
