18. A. stenophýlla, Gray. Puberulent, but foliage glabrous; stems slender (1–2° high), leaves narrowly linear (3–7´ long, 1–2½´´ wide), the upper alternate, lower opposite; umbels several, short-peduncled, 10–15-flowered; corolla-lobes oblong, greenish; hoods whitish, equalling the anthers, conduplicate-concave; follicles erect on ascending pedicels.—Dry prairies, Neb. to E. Kan., south and westward.
3. ACERÀTES, Ell. Green Milkweed.
Nearly as in Asclepias; but the hoods destitute of crest or horn (whence the name, from α privative, and κέρας, a horn).—Flowers greenish, in compact many-flowered umbels. Leaves opposite or irregularly alternate, short-petioled or sessile. Pollen-masses slender-stalked. Follicles smooth, slender.
[*] Crown upon a short column and shorter than the globular mass of anthers and stigma, leaves mainly alternate-scattered.
1. A. longifòlia, Ell. Minutely roughish-hairy or smoothish; stem erect (1–3° high), very leafy; leaves linear (3–7´ long); umbels lateral, on peduncles of about the length of the slender pedicels; flowers 3´´ long when expanded.—Moist prairies and pine-barrens, Ohio to Minn., south to Fla. and Tex. July–Oct.
[*][*] Crown sessile, the oblong hoods nearly equalling the anthers; leaves often opposite and broader.
2. A. viridiflòra, Ell. Minutely soft-downy, becoming smoothish; stems ascending (1–2° high); leaves oval to linear, thick (1½–4´ long); umbels nearly sessile, lateral, dense and globose; flower (when the corolla is reflexed) nearly ½´ long, short-pedicelled.—Dry soil, common, especially southward. July–Sept.—Runs into var. lanceolàta, Gray, with lanceolate leaves 2½–4´ long;—and var. lineàris, Gray, with elongated linear leaves and low stems; umbels often solitary. The latter form from Minn., Dak., and southward.
3. A. lanuginòsa, Decaisne. Hairy, low (5–12´ high); leaves lanceolate or ovate-lanceolate; umbel solitary and terminal, peduncled; flowers smaller; pedicels slender.—Prairies, N. Ill. to Minn., and westward. July.
4. ENSLÉNIA, Nutt.
Calyx 5-parted. Corolla 5-parted; the divisions erect, ovate-lanceolate. Crown of 5 free membranaceous leaflets, which are truncate or obscurely lobed at the apex, where they bear a pair of flexuous awns united at base. Anthers nearly as in Asclepias; pollen-masses oblong, obtuse at both ends, fixed below the summit of the stigma to the descending glands. Follicles oblong-lanceolate, smooth. Seeds with a tuft, as in Asclepias.—A perennial twining herb, smooth, with opposite heart-ovate and pointed long-petioled leaves, and small whitish flowers in raceme-like clusters, on slender axillary peduncles. (Dedicated to A. Enslen, an Austrian botanist who collected in the Southern United States early in the present century.)