Herbs, perennial, often from somewhat thickened rhizomes; latex milky. Stems erect or ascending, unarmed, glabrous or eglandular-pubescent. Leaves deciduous, opposite or rarely subopposite or subverticillate, petiolate; stipular colleters interpetiolar; laminar colleters absent. Inflorescences axillary or terminal, cymose, pedunculate, bracteate or ebracteate. Flowers: calycine colleters absent; corolla white, white with pink veins, greenish white, yellowish white, or pink, campanulate, urceolate, or cylindric, aestivation dextrorse; corolline corona of 5 small sagittate squamellae; androecium and gynoecium not united into a gynostegium; stamens inserted near base of corolla tube; translators absent; anthers connivent, adherent to stigma; connectives enlarged, narrowly 2-lobed, locules 4; pollen in tetrads, not massed into pollinia, translators absent; nectaries 5, distinct. Fruits follicles, usually paired, erect, brown, slender, terete, surface striate, glabrous. Seeds fusiform, terete, not winged, not beaked, comose, not arillate. x = 8, 11.

Distribution

North America, n Mexico.

Discussion

Species 3 (3, including 1 hybrid, in the flora).

Apocynum is a taxonomically challenging genus in which the number of species recognized depends upon both generic and species delimitations. Nearly 250 specific and infraspecific taxa have been named in Apocynum, many by E. L. Greene (for example, 1904, 1912), that were later reduced by R. E. Woodson Jr. (1930) to seven species and 17 varieties, and more recent floras have recognized as few as two variable species. The present treatment conservatively views Apocynum as comprising three species native to North America and northern Mexico, with the Old World species placed in the segregate genera Poacynum Baillon and Trachomitum Woodson, following Woodson. A detailed discussion of the nomenclatural history, morphology, anatomy, and geography of Apocynum was provided by Woodson.

The species of Apocynum are often weedy and clonal and a single genetic individual can be spread over a large area. Although visited by a variety of potential pollinators (K. D. Waddington 1976), fruit set in Apocynum species is low, often less than 10%. S. R. Lipow and R. Wyatt (1999) have suggested that this is due to a late-acting self-incompatibility mechanism similar to that documented for other members of the family.

Apocynum has a long history of usage by humans, especially Native Americans, as a source of fiber for the production of thread and cord used in the manufacture of items such as netting, basketry, bowstrings, bridles, and rope. A high-quality rubber latex has been extracted from A. androsaemifolium and A. cannabinum and was used in the preparation of chewing gum by several Native American groups. The mild toxicity of Apocynum species is due to the presence of cardiac glycosides, and powdered roots, or root and leaf extracts, were used by Native Americans to treat a wide variety of disorders, including headache, asthma, dyspepsia, constipation, renal and cardiac conditions, and intestinal worms (S. Cheatham et al. 1995; G. E. Burrows and R. J. Tyrl 2013).

Selected References

None.

Lower Taxa

Apocynum androsaemifolium, Apocynum cannabinum, Apocynum ×floribundum

Key

1	Corollas white, greenish white, or yellowish white, tube 1.5–2.5 mm; inflorescences usually not exceeding foliage; leaf blades mostly more than 2.5 times as long as wide.	Apocynum cannabinum
1	Corollas pink, white with pink veins, or white tinged with pink, tube 4–5 mm; inflorescences usually exceeding foliage; leaf blades mostly less than 2 times as long as wide.	> 2
2	Corolla tubes 3 times as long as calyx lobes or longer; seeds 1.5–2 mm; leaves drooping or spreading.	Apocynum androsaemifolium
2	Corolla tubes 1.5–2 times as long as calyx lobes; seeds 3–4 mm; leaves spreading to ascending.	Apocynum × floribundum