Flora of North America species comparison

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Asclepias arenaria

sand milkweed
Habit Herbs.
Stems

1–8, spreading or decumbent to erect, unbranched or rarely branched near base, 20–100 cm, tomentose, not glaucous, rhizomatous.
Leaves

opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole plus 0–4 in axil;

petiole 7–17 mm, tomentose;

blade oblong or obovate to ovate or oval, 4.2–11.5 × 2.5–7.5 cm, subcoriaceous, base rounded or truncate to subcordate, margins often undulate or crisped, apex truncate to rounded (rarely acute), sometimes emarginate, often mucronate, venation brochidodromous, surfaces tomentose to nearly glabrate, margins ciliate, 12–24 laminar colleters.
Inflorescences

extra-axillary (sometimes appearing terminal), sessile or pedunculate, 14–51-flowered;

peduncle 0–2 cm, tomentose, with 1 caducous bract at the base of each pedicel.
Pedicels

15–25 mm, densely tomentose.
Flowers

erect to pendent;

calyx lobes lanceolate, 2.5–3 mm, apex acute, densely tomentose;

corolla green to yellowish green, sometimes tinged reddish or purplish, lobes reflexed with spreading tips, oval, 7–8 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;

gynostegial column 1–2 mm;

fused anthers green, obconic, 2–2.5 mm, wings right-triangular, closed, apical appendages ovate;

corona segments cream to greenish cream or ochroleucous, subsessile, conduplicate, flaring at base, 3.5–4 mm, exceeding style apex, apex truncate to rounded, emarginate, minutely papillate, proximal margin toothed, internal appendage falcate, exserted, sharply incurved over style apex, apex upturned, minutely papillose.
Seeds

oval, 9–12 × 6–8 mm, margin winged, faces minutely rugulose;

coma 2–3 cm.
Follicles

erect on upcurved pedicels, lance-ovoid, 5.5–10 × 2–2.8 cm, apex acuminate, smooth, pilosulous.

Asclepias arenaria
Phenology Flowering May–Aug(–Oct); fruiting Jul–Sep(–Oct).
Habitat Sandhills, dunes, sandy soils, prairies, pastures, grasslands, oak scrub, riparian areas.
Elevation 100–1900 m. (300–6200 ft.)
Distribution
from FNA
CO; KS; NE; NM; OK; SD; TX; WY; Mexico (Chihuahua)
[WildflowerSearch map]
[BONAP county map]
Discussion

Asclepias arenaria is the milkweed most consistently associated with pure sand soils in the western Great Plains. It is predictably found at the bases of stabilized and semi-stabilized dunes. Flowers of this species are visited by a variety of Hymenoptera, notably several species of large wasps, including tarantula hawk wasps (Pepsinae, Pompilidae) and scoliid wasps (Scoliidae), as well as by Lepidoptera. Non-flowering shoots of A. arenaria may produce linear leaves; they are easily overlooked and not identified as belonging to this species unless one is aware of this variation, especially when they are produced on rhizomes distant from shoots with typical foliage. This trait is found in several other broad-leaved milkweeds (for example, A. erosa, A. welshii). Asclepias arenaria is rare and considered to be of conservation concern in Wyoming, where it has been recorded from only two sites in Goshen County.

(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. 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. perennis, 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 Torrey in W. H. Emory: Rep. U.S. Mex. Bound. 2(1): 162. (1859)
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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