Flora of North America species comparison

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Asclepias perennis

aquatic milkweed, aquatic or white swamp or swamp or thin-leaf milkweed
Habit Subshrubs or herbs, cespitose.
Stems

1–5, erect, sparsely to moderately branched, especially towards base, 30–60 cm, puberulent with curved trichomes in a line to glabrate, not glaucous, rhizomatous.
Leaves

persistent or gradually caducous from the base, opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;

petiole 10–12 mm, ciliate;

blade narrowly elliptic to oval or oblong, 5–14 × 0.3–3 cm, membranous or chartaceous, base cuneate, margins entire, apex acute to attenuate or acuminate, minutely mucronate, venation faintly brochidodromous to eucamptodromous, surfaces sparsely puberulent with curved trichomes, more densely on veins, to glabrate, margins inconspicuously ciliate, laminar colleters absent.
Inflorescences

extra-axillary at upper nodes, sometimes appearing terminal, pedunculate, 12–30-flowered;

peduncle 1.5–5 cm, puberulent with curved trichomes, sometimes only on 1 side, with 1 caducous bract at the base of each pedicel.
Pedicels

7–13 mm, puberulent with curved trichomes, sometimes only on 1 side.
Flowers

erect to spreading;

calyx lobes narrowly lanceolate to linear, 1.2–1.5 mm, apex acute, puberulent with curved trichomes;

corolla white to pink-tinged, lobes reflexed with spreading tips, elliptic, 3–4 mm, apex acute to obtuse, glabrous abaxially, minutely papillose at base adaxially;

gynostegial column 0.8–1.2 mm;

fused anthers brown, cylindric, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;

corona segments white, sometimes faintly pink-tinged, stipitate, tubular, dorsally rounded, 1.5–2.5 mm, slightly exceeding style apex, apex obtuse to acute, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;

style apex shallowly depressed, white, sometimes pink-tinged.
Seeds

broadly oval, 12–15 × 11–14 mm, margin broadly winged, faces smooth;

coma absent.
Follicles

pendulous on declined pedicels, lance-ovoid, 4–7 × 1–2.5 cm, apex long-acuminate, smooth, glabrous.

Asclepias perennis
Phenology Flowering (Mar–)Apr–Nov; fruiting Jun–Dec.
Habitat Swamps, streamsides, ditches, bottomlands, flood plains, marshes, saturated or inundated clay, silty, and sandy soils, pine-oak, oak, and mixed hardwood for­ests, riparian woods, pine flatwoods.
Elevation 0–300(–500?) m. (0–1000(–1600?) ft.)
Distribution
from FNA
AL; AR; FL; GA; IL; IN; KY; LA; MO; MS; SC; TN; TX
[WildflowerSearch map]
[BONAP county map]
Discussion

Asclepias perennis is the most hydrophytic North American milkweed and is often found emerging from standing water in swamps and ditches. The pendulous fruits and hairless seeds are distinctive; it is the only milkweed in the United States with seeds lacking a coma, and only one of three such species in North America. It is widely distributed along the coastal plain; inland (Arkansas, Illinois, Indiana, Kentucky, Missouri, Tennessee), it is restricted to the valleys of the Mississippi and Ohio rivers and their tributaries.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 14.
Parent taxa Apocynaceae > Asclepias
Sibling taxa
A. albicans, A. amplexicaulis, A. angustifolia, A. arenaria, A. asperula, A. brachystephana, A. californica, A. cinerea, A. connivens, A. cordifolia, A. cryptoceras, A. curassavica, A. curtissii, A. cutleri, A. eastwoodiana, A. elata, A. emoryi, A. engelmanniana, A. eriocarpa, A. erosa, A. exaltata, A. fascicularis, A. feayi, A. hallii, A. hirtella, A. humistrata, A. hypoleuca, A. incarnata, A. involucrata, A. labriformis, A. lanceolata, A. lanuginosa, A. latifolia, A. lemmonii, A. linaria, A. linearis, A. longifolia, A. macrosperma, A. macrotis, A. meadii, A. michauxii, A. nummularia, A. nyctaginifolia, A. obovata, A. oenotheroides, A. ovalifolia, A. pedicellata, A. prostrata, A. pumila, A. purpurascens, A. quadrifolia, A. quinquedentata, A. rubra, A. rusbyi, A. ruthiae, A. sanjuanensis, A. scaposa, A. solanoana, A. speciosa, A. sperryi, A. stenophylla, A. subulata, A. subverticillata, A. sullivantii, A. syriaca, A. texana, A. tomentosa, A. tuberosa, A. uncialis, A. variegata, A. verticillata, A. vestita, A. viridiflora, A. viridis, A. viridula, A. welshii
Name authority Walter: Fl. Carol., 107. (1788)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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