Alnus glutinosa
Alnus oblongifolia
black alder, European alder, European black alder
aliso (Mexico), Arizona alder, New Mexican alder, oblong leaf alder
dark brown, smooth, becoming darker and breaking into shallow fissures in age;
lenticels pale, horizontal.
dark gray, smooth, becoming blackish and breaking into shallow vertical plates in age;
lenticels inconspicuous.
blade obovate to nearly orbiculate, 3–9 × 3–8 cm, leathery, base obtuse to broadly cuneate, margins flat, coarsely and often irregularly doubly serrate to nearly dentate, major teeth acute to obtuse or rounded, apex often retuse or obcordate, or occasionally rounded;
surfaces abaxially glabrous to sparsely pubescent, often more heavily on veins, both surfaces heavily resin-coated.
blade narrowly ovate or lanceolate to narrowly elliptic, 5–9 × 3–6 cm, leathery, base narrowly to broadly cuneate or narrowly rounded, margins flat, sharply and coarsely doubly serrate, rarely evenly and densely short-serrate, major teeth sharp, acuminate, secondary teeth distinctly larger, apex long to short-acuminate, rarely acute;
surfaces abaxially glabrous to sparsely pubescent or infrequently villous, moderately resin-coated.
formed season before flowering and exposed during winter; staminate catkins in 1 or more clusters of 2–5, 4–13 cm; pistillate catkins in 1 or more clusters of 2–5.
formed season before flowering and exposed during winter; staminate catkins in 1 or more clusters of 3–6, 3.5–10 cm; pistillate catkins in 1 or more clusters of 2–7.
ovoid to nearly globose, 1.2–2.5 × 1–1.5 cm;
peduncles 1–10(–20) mm.
ovoid, ellipsoid, or nearly cylindric, 1–2.5 × 0.8–1.5 cm;
peduncles 5–10 mm.
buds stipitate, ellipsoid to obovoid, 6–10 mm, apex obtuse;
stalks 2–5 mm;
scales 2–3, outer 2 equal, valvate, usually heavily resin-coated.
buds stipitate, ovoid, 4–8 mm, apex rounded;
stalks 1.5–4 mm;
scales 2, equal, valvate, sometimes incompletely covering underlying leaves, moderately resin-coated.
before new growth in spring.
before new growth in spring.
obovate, wings reduced to narrow, thickened ridges.
elliptic to obovate, wings narrower than body, irregular in shape, leathery.
= 28.
Alnus glutinosa
Alnus oblongifolia
Alnus glutinosa is cultivated as an ornamental tree throughout eastern North America and is available in a variety of cultivars, including cut-leafed and compact-branching forms. This species has also been used extensively to control erosion and improve the soil on recently cleared or unstable substrates, such as sand dunes and mine spoils. It has escaped and become widely naturalized throughout the temperate Northeast, occasionally becoming a weedy pest. In Europe the black alder has served for many centuries as an important source of hardwood for timbers and carved items, including wooden shoes.
Alnus glutinosa has been called A. vulgaris Hill in some older literature; that name was not validly published.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Alnus oblongifolia is closely related to the Mexican and Central American A. acuminata, with which it has sometimes been confused. It is found only in scattered populations in the temperate deciduous forest vegetation zone of high mountains in the arid Southwest.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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