Asclepias fascicularis
Asclepias tomentosa
Mexican whorled milkweed, narrow-leaf milkweed, narrow-leaf or Mexican or Mexican whorled milkweed
tuba milkweed, velvetleaf milkweed
few–numerous, erect, sparsely to moderately branched, 50–150 cm, glabrous, not glaucous, rhizomes absent.
solitary (rarely 2), erect, unbranched (rarely branched), 25–150 cm, densely puberulent with curved trichomes, 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, petiolate, with 1 stipular colleter on each side of petiole;
petiole 2–9 mm, densely puberulent with curved trichomes;
blade lanceolate or ovate to oval or oblong or elliptic to oblanceolate or obovate, 3.5–10 × 1–5 cm, chartaceous, base obtuse to subcordate, margins crisped, apex acute or obtuse to truncate or emarginate, sometimes mucronate, venation eucamptodromous to brochidodromous, surfaces puberulent with curved trichomes to tomentulose, margins ciliate, 4–8 laminar colleters.
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, 5–37-flowered;
peduncle 0–0.3 cm, densely puberulent with curved trichomes to tomentulose, with 1 caducous bract at the base of each pedicel.
9–14 mm, puberulent with curved trichomes to pilosulous.
12–19 mm, densely pilose to tomentulose.
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;
calyx lobes lanceolate, 3–4 mm, apex acute, pilose;
corollas green, often tinged reddish or purplish, lobes reflexed with spreading tips, oval, 7–9 mm, apex acute, glabrous;
gynostegial column 0.5–1 mm;
fused anthers green, obconic, 3–4 mm, wings broadly right-triangular, closed, apical appendages broadly oval;
corona segments green with cream apex, often tinged pink or purple, stipitate, conduplicate, dorsally flattened, 3–4 mm, exceeded by style apex, apex truncate, glabrous, internal appendage falcate, exserted, sharply inflexed towards style apex, papillose;
style apex shallowly depressed, green, fading pink or red.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 6.5–8 × 4.5–6 mm, margin winged, remotely erose, faces minutely and sparsely papillose and rugulose;
coma 3–3.5 cm.
erect on straight pedicels, fusiform, 6–9 × 0.5–1 cm, apex attenuate, smooth, glabrous.
erect on upcurved pedicels, fusiform to narrowly lance-ovoid, 9–18 × 1–1.5 cm, apex long-acuminate, smooth, puberulent with curved trichomes to pilosulous or tomentulose.
= 22.
Asclepias fascicularis
Asclepias tomentosa
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.)
Asclepias tomentosa is restricted largely to coastal and inland sandhills. As described by B. A. Sorrie (2016), it exhibits a disjunct distribution, with gaps of unoccupied, but suitable, habitat in eastern Georgia and from the western Florida Panhandle to Louisiana. Sorrie reports a specimen from Alabama, but this cannot be found. When not in flower, A. tomentosa can be confused with A. curtissii in peninsular Florida, where they sometimes co-occur in close proximity, and with A. obovata on the Gulf Coastal Plain. It can be distinguished from A. curtissii by the usually larger and more densely vestitured leaf blades. Both species may have purple stems. Asclepias obovata can be distinguished from A. tomentosa by the hirtellous to velutinous vestiture of the herbage. Outside of Florida, populations of A. tomentosa are few, but it has not been considered to be of conservation concern; evaluation of its status in Texas and Georgia (known only from Coffee County) may be warranted.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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