Asclepias longifolia
Asclepias exaltata
Florida milkweed, long-leaf milkweed
asclépiade très grande, poke milkweed, tall milkweed
1–few, spreading to decumbent, unbranched, 25–70 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1–3+, erect, unbranched, 65–150 cm, sparsely pubescent to glabrate, not glaucous, rhizomes absent.
opposite or alternate, sessile or petiolate, with 1 or 2 stipular colleters on each side of petiole, also in axil;
petiole 0–2 mm, puberulent with curved trichomes;
blade linear to linear-lanceolate, 5–18 × 0.2–1 cm, chartaceous, base cuneate, margins entire, apex acute to attenuate, sometimes mucronate, venation brochidodromous, surfaces scabridulous to puberulent with curved trichomes, especially on veins, margins ciliate, laminar colleters absent.
opposite (rarely whorled at 1 midstem node), petiolate, with 1 stipular colleter on each side of petiole;
petiole 5–15 mm, minutely puberulent with curved trichomes to glabrate;
blade broadly ovate to oblong or elliptic, 10–24 × 2–11 cm, membranous, base cuneate, margins entire, apex attenuate to acuminate, venation eucamptodromous to brochidodromous, surfaces pilosulous to glabrate abaxially, sparsely pilosulous to glabrate adaxially, densely so on veins, margins ciliate, 6–10 laminar colleters (often obscured in pressed specimens).
terminal and extra-axillary at upper nodes, sessile or pedunculate, 13–28(–36)-flowered;
peduncle 0–6 cm, puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
extra-axillary at upper nodes (terminal), pedunculate, 11–41-flowered;
peduncle 0.5–8.5 cm, puberulent on 1 side with curved trichomes, with 1 caducous bract at the base of each pedicel.
9–16 mm, puberulent with curved trichomes.
25–45 mm, puberulent with curved trichomes to pilosulous on 1 side.
erect to spreading;
calyx lobes narrowly lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes;
corolla white to greenish cream, purple at lobe tips, lobes reflexed, oblong, 3–5 mm, apex obtuse, glabrous;
gynostegial column 0.2–0.5 mm;
fused anthers green or brown, cylindric, 1–1.5 mm, wings triangular to trapezoidal, widest at middle, slightly open at tip, apical appendages ovate;
corona segments pinkish lavender to red-violet, often with white apex, often a darker red-violet stripe or at base, sessile, laminar, strongly dorsally compressed, margins incurved, appressed to column, curved to subsaccate, 2–2.5 mm, exceeding point of anther wings, greatly exceeded by style apex, apex obtuse to truncate, glabrous, internal appendage absent or obscure, glabrous;
style apex shallowly depressed, greenish cream to green.
spreading to drooping;
calyx lobes narrowly lanceolate, 3–4.5 mm, apex attenuate, pilosulous;
corolla green (rarely pink-tinged), lobes reflexed, sometimes with spreading tips, elliptic, 6–12 mm, apex acute, glabrous;
gynostegial column 1.5–2 mm;
fused anthers green, columnar, 2.5–3.5 mm, wings right-triangular with rounded tip, apical appendages deltoid;
corona segments white to pinkish, sometimes red-purple at base, stipitate, tubular, 3–5 mm, exceeding style apex, base saccate, apex truncate with 1–2 teeth on each side, glabrous, internal appendage falcate, exserted, arching above style apex, glabrous;
style apex shallowly depressed, green or cream.
ovate, 11–12 × 7–8 mm, margin winged, faces smooth;
coma 4–5 cm.
lance-ovate, 8–10 × 4–6 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
erect on upcurved pedicels, narrowly fusiform, 8–13.5 × 0.7–1.2 cm, apex attenuate, smooth, puberulent with curved trichomes.
erect on upcurved pedicels, fusiform, 10–15 × 1.5–2 cm, apex long-acuminate, smooth, puberulent with curved trichomes.
= 22.
Asclepias longifolia
Asclepias exaltata
Asclepias longifolia has sometimes been treated to include A. hirtella as conspecific, as discussed under that species. As circumscribed here, the distribution of A. longifolia extends along the Atlantic Coastal Plain south of Delaware to Florida and westward to the Mississppi River. Reports of A. longifolia from west of the Mississippi River in Louisiana and in Texas are assigned here to A. hirtella. Hence, the range of A. longifolia in Louisiana is extremely limited, and the conservation status of this species warrants assessment in that state (Livingston, Saint Helena, Saint Tammany, Tangipahoa, and Washington parishes). Reports of A. longifolia from Maryland and West Virginia have not been confirmed, and the species is considered extirpated from Delaware. Otherwise, it is rare at the northern extent of its range and considered to be of conservation concern in North Carolina and Virginia (Greensville and Prince George counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Unlike the other common deciduous forest understory milkweeds, the range of Asclepias exaltata does not extend to the Ozarks. Compared to these other species, A. exaltata seems to prefer richer soils. Non-flowering individuals are often confused with A. purpurascens, from which they are distinguished by leaves with thinner texture, sparser abaxial vestiture, and longer-tapered apices. Hybrids with A. syriaca are well established at several disjunct locations (S. R. Kephart et al. 1988), and their genetics and pollination have been studied (S. B. Broyles 2002; T. M. Stoepler et al. 2012). Hybrids with A. purpurascens and A. amplexicaulis are also known, but appear to be rare and local. Putative hybrids exhibit intermediate floral and vegetative morphology. Asclepias exaltata is rare at the margins of its range and is considered to be of conservation concern in Alabama (Lawrence, Madison, and Winston counties), Delaware (New Castle County), Rhode Island, and Quebec. Recently, it has been documented at a single site in Missouri (Cape Girardeau County) and should be considered to be of conservation concern in that state, too.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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