7. Frangula alnus Miller, Gard. Dict. ed. 8. Frangula no. 1. 1768.
Glossy buckthorn, European alder-buckthorn Glossy buckthorn, European alder-buckthorn
Rhamnus frangula Linnaeus, Sp. Pl. 1: 193. 1753
Shrubs or small trees, 2–5(–7) m. Stems greenish to brown, sparsely puberulent, glabrescent. Leaves deciduous; petiole 10–19 mm; blade dull green abaxially, glossy darker green adaxially, broadly elliptic-obovate to broadly elliptic or broadly oblong, 4–7(–11) cm, herbaceous, base cuneate to rounded, margins entire, apex rounded to acute or abruptly short-acuminate, abaxial surface sometimes minutely strigose along midveins, adaxial surface glabrous; secondary veins 6–10 pairs. Inflorescences fascicles, sessile, 1–8-flowered. Pedicels 3–10 mm. Stigmas 2–3-lobed. Drupes black, globose or slightly elongate, 6–8 mm; stones 2(–3). 2n = 20–26.
Flowering May–Sep. Alkaline and acid tamarack, red maple and cedar swamps, peatlands, bogs, fens, disturbed areas, riparian thickets, lakeshores, ditches, fencerows, hedgerows, low woods, beaver meadows; 10–400 m; introduced; Man., N.B., N.S., Ont., P.E.I., Que., Sask.; Colo., Conn., Idaho, Ill., Ind., Iowa, Ky., Maine, Mass., Mich., Minn., Nebr., N.H., N.J., N.Y, Ohio, Pa., R.I., Tenn., Vt., W.Va., Wis., Wyo.; Europe; introduced also in Asia (China, Russia), n Africa.
Two horticultural forms of Frangula alnus are widely sold and planted in North America. The cultivar 'Asplenifolia' (F. alnus var. asplenifolia Dippel; fern leaf or cutleaf buckthorn) has linear-oblong leaves with coarsely toothed to incised margins and commonly is grown as a specialty plant. The cultivar 'Columnaris' (tallhedge glossy buckthorn) has a narrow, upright habit and is used in hedging. Both forms were noted by M. H. Brand (http://www.hort.uconn.edu/plants/r/rhafra/rhafra1.html) to spread invasively by seeds. 'Asplenifolia' has been reported as naturalized in Ontario (A. W. Dugal 1989, 1992), Illinois (A. Branhagen, pers. comm.), and Ohio (M. K. Delong et al. 2005).