Asclepias viridiflora
Asclepias hirtella
asclépiade à fleurs vertes, green antelopehorn milkweed, green comet milkweed, green milkweed
asclépiade hérissée, green milkweed, prairie milkweed, tall green milkweed
solitary, erect to ascending, unbranched (rarely), (10–)20–125 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1–3+, erect to spreading, unbranched (rarely branched), 30–125 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
opposite to subopposite, sessile or petiolate, with 1 or 2 stipular colleters on each side of petiole and also in axil;
petiole 0–5 mm, puberulent with curved trichomes;
blade linear to broadly oval or nearly orbiculate, 2–13 × 0.8–6 cm, chartaceous, base cuneate to rounded, margins entire or crisped, apex acute or obtuse to truncate or emarginate, mucronate, venation brochidodromous, surfaces sparsely pilosulous to glabrate, margins ciliate, laminar colleters absent.
opposite or alternate, sessile or petiolate, with 1–3 stipular colleters on each side of petiole, also in axil;
petiole 0–3 mm, puberulent with curved trichomes;
blade linear to linear-lanceolate, 4–16 × 0.2–1.5 cm, chartaceous, base cuneate, margins entire, apex acute to attenuate, mucronate, venation faintly brochidodromous, surfaces scabridulous to puberulent with curved trichomes, especially on veins, margins ciliate, laminar colleters absent.
extra-axillary at upper nodes, sometimes branched at peduncle apex, sessile or pedunculate, 22–60-flowered;
peduncle 0–4 cm, puberulent with curved trichomes to pilosulous, with 1 caducous bract at the base of each pedicel.
extra-axillary, sessile or pedunculate, 34–112-flowered;
peduncle 0–4 cm, hirtellous, with 1 caducous bract at the base of each pedicel.
7–13 mm, pilosulous.
11–23 mm, hirtellous.
erect to pendent;
calyx lobes narrowly lanceolate, 2–3 mm, apex acute, pilosulous;
corolla green to yellowish green, sometimes tinged red, lobes reflexed, oblong, 5–7 mm, apex acute, inconspicuously pilosulous at apex abaxially, glabrous adaxially;
gynostegium sessile;
fused anthers green, cylindric, 3–4 mm, wings triangular, widest at middle, closed, apical appendages ovate, marginally inflexed, apically deflexed;
corona segments green to cream, sometimes tinged red, sessile, laminar, margins incurved, appressed to column, 3–4 mm, greatly exceeded by style apex, apex obtuse, glabrous, internal appendage absent or obscure, glabrous;
style apex shallowly depressed, green.
erect to pendent;
calyx lobes lanceolate, 1.5–2 mm, apex acute, hirtellous;
corolla green to greenish cream, red-violet at tip, lobes reflexed, oblong, 3–5 mm, apex obtuse, glabrous;
gynostegial column 0.5–1 mm;
fused anthers green, cylindric, 1–1.5 mm, wings trapezoidal, closed, apical appendages oblate;
corona segments cream to greenish cream, rarely pinkish lavender or brown, often with a dorsal red-violet stripe or at base, sessile, laminar, strongly dorsally compressed, margins incurved, appressed to column, saccate, 1.5–2 mm, not exceeding point of anther wings, greatly exceeded by style apex, apex truncate, glabrous, internal appendage absent or obscure, glabrous;
style apex shallowly depressed, green.
ovate, 7–8 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 10–11 × 7–8 mm, margin winged, faces smooth;
coma 3.5–4 cm.
erect on upcurved pedicels, fusiform to lance-ovoid, 6–10 × 1.5–2 cm, apex acuminate to attenuate, smooth, pilosulous.
erect on upcurved pedicels, fusiform, 6–15 × 1–2 cm, apex attenuate, smooth, pilosulous to puberulent with curved trichomes.
= 22.
Asclepias viridiflora
Asclepias hirtella
Asclepias viridiflora is one of the milkweeds with spherical, greenish umbels and inconspicuous coronas (see also A. engelmanniana, A. hirtella, A. lanuginosa, A. longifolia, A. rusbyi, A. stenophylla). Prior to close examination, the tight green balls of open flowers appear to be merely in bud. The diversity in leaf morphology among individuals (linear to orbiculate) is remarkable, but has no taxonomic significance—the full range of variation may be found within single populations. This is the most widespread milkweed within the flora area, ranging across most of the United States (absent only from the westernmost states and most of New England) and southern Canada. It is nowhere abundant, but may be regularly encountered in suitable, thin-soiled prairie habitats, especially in the Great Plains. It is rare and considered to be of conservation concern on the margins of its range, in Alberta (Cypress, Forty Mile, and Warner counties), Arizona (Coconino, Gila, and Yavapai counties), Connecticut (New Haven County), Florida (Gadsden and Jackson counties), and New York (Columbia, Nassau, Richmond, and Suffolk counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias hirtella has been included sometimes in a broadly circumscribed A. longifolia. The species are parapatric and usually are readily distinguished by the hirtellous pedicels of A. hirtella and puberulent pedicels with curved trichomes of A. longifolia. Asclepias hirtella is also typically much taller with more numerous umbels compared to A. longifolia. However, populations along the Gulf Coastal Plain from eastern Texas to the Mississippi River and from southern Mississippi to central Georgia have proved challenging because they include plants with the growth form of A. longifolia and the pedicel vestiture of A. hirtella. Consequently, these populations have not been consistently assigned to one species or the other. However, the previously overlooked difference in corona segment length correlates perfectly with the pedicel vestiture and with geography. Thus, Gulf Coast populations west of the Mississippi River and north of the immediate coastline are here interpreted to represent short-statured A. hirtella. This hypothesis warrants investigation with population genetic data—it is quite possible that populations of A. hirtella in southern Arkansas, Louisiana, and Texas merit recognition as a subspecies. Asclepias hirtella is rare at the margins of its range and is considered to be of conservation concern in Georgia, Kentucky, Louisiana, Michigan, Minnesota (Mower County), Mississippi, Tennessee, West Virginia (Jackson, Mason, and Putnam counties), and Ontario (Essex County).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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