Asclepias fascicularis
Asclepias viridula
Mexican whorled milkweed, narrow-leaf milkweed, narrow-leaf or Mexican or Mexican whorled milkweed
green milkweed, southern milkweed
few–numerous, erect, sparsely to moderately branched, 50–150 cm, glabrous, not glaucous, rhizomes absent.
1 (rarely 2), erect, unbranched, 25–75 cm, minutely puberulent in a line with curved trichomes to glabrate, 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.
opposite, sessile, with 1 or 2 stipular colleters on each side of leaf base;
blade linear to filiform, 4.5–9 × 0.15–0.25 cm, membranous, base cuneate, margins revolute, apex acute, mucronate, venation obscure, surfaces glabrous, margins sparsely ciliate to glabrate, 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 at upper nodes, pedunculate, 4–15-flowered;
peduncle 0.8–2 cm, minutely puberulent in a line with curved trichomes, with 1 caducous bract at the base of each pedicel.
9–14 mm, puberulent with curved trichomes to pilosulous.
7–13 mm, minutely puberulent in a line with curved trichomes.
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 lanceolate, 1.5–2.5 mm, apex acute, glabrous;
corolla green, tinged brown, lobes reflexed with spreading tips, elliptic, 3–5 mm, apex acute to obtuse, sometimes emarginate, glabrous;
gynostegial column 0.8–1 mm;
fused anthers green and brown, cylindric, 1.5–2 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream, tinged brown or green, stipitate, conduplicate and dorsally rounded, 3–4 mm, slightly exceeding style apex, apex acute, spreading, with a proximal tooth on each side, glabrous, internal appendage falcate, exserted, arching towards style apex, glabrous;
style apex shallowly depressed, green.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 8–9 × 5–6 mm, margin winged, faces minutely and sparsely rugulose;
coma 2.5–3 cm.
erect on straight pedicels, fusiform, 6–9 × 0.5–1 cm, apex attenuate, smooth, glabrous.
erect on straight pedicels, fusiform, 9–12.5 × 0.6–0.9 cm, apex long-acuminate, smooth, glabrous.
= 22.
Asclepias fascicularis
Asclepias viridula
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.)
Similarities among Asclepias cinerea, A. feayi, and A. viridula are discussed under those species; all three are slender, cryptic when not in flower, and appear to emerge and flower in response to precipitation and fire events. Asclepias viridula is perhaps the most cryptic of the three, by virtue of its green corollas, and it is the most limited in range. It is typically found in wetter sites than co-occurring A. cinerea. Asclepias viridula is found disjunctly in northeastern Florida and the Florida Panhandle. Its range barely crosses into Alabama, where it is known from a single site in Houston County. Reports from Georgia are probably based on misidentifications—no specimens are known, and further searches for A. viridula in Georgia are warranted. It is considered to be of conservation concern throughout its range. Although not listed as a threatened or endangered species under the ESA in the United States, the number of populations is low and merits further study of population persistence and viability.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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