1. Alnus glutinosa (L.) Gaertn. (black alder, European alder)

Map 1274

Plants trees 4–15 m tall, the bark medium gray, smooth on younger branches but fissured with age. Twigs with the buds 5–7 mm long (excluding the stalk). Petioles 11–32 mm long (the longest petioles on a branch always longer than 2 cm). Leaf blades usually almost circular, occasionally very broadly obovate, 4–12 cm long, 4–10 cm wide, the base rounded to broadly narrowed, the tip shallowly notched, truncate, or occasionally broadly rounded, the margins coarsely toothed and sometimes also with small, shallow lobes, the largest teeth 0.6–7.0 mm long, each side of the midrib with 6–8 strong secondary veins. Conelike infructescences 1.5–3.0 cm long, the fruits 3–5 mm long (including the styles), narrowly winged. 2n=28. March–April.

Introduced, known thus far only from a single specimen from Greene County (native of Europe; naturalized in the northeastern U.S. from Massachusetts and Tennessee west to Minnesota and Missouri). Margins of a lake.

Black alder is tolerant of waterlogged soil and is sold as an ornamental for wet or boggy soil, especially in the cooler parts of the northeastern United States. It has escaped over a wide region in the northeastern states and has become a pest at a few sites, but is known as an escape thus far at only one locality in Missouri, along the shore of Lake Springfield in Springfield.

The wood of black alder is durable when continually wet or submerged, and in Europe it was traditionally the wood of choice for pilings and foundations in saturated or submerged soil. The pilings that support the old city of Venice and parts of Amsterdam are mostly black alder. It is a poor conductor of heat, and is the wood of choice for wooden shoes. It also has been used for furniture and small carved or turned items.