Alnus glutinosa
Alnus maritima
black alder, European alder, European black alder
brook alder, seaside alder
dark brown, smooth, becoming darker and breaking into shallow fissures in age;
lenticels pale, horizontal.
light gray, smooth;
lenticels small, 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 elliptic, oblong, or narrowly obovate, 4.5–9 × 2–5 cm, leathery, base acute to cuneate, margins flat, teeth low, single, relatively distant, apex acute, obtuse, or rounded;
surfaces abaxially mostly glabrous, resin-coated when young.
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.
catkins formed during same season as flowering; staminate catkins in 1 terminal cluster of 2–4, 2–6 cm; pistillate catkins solitary in leaf axils proximal to staminate catkins.
ovoid to nearly globose, 1.2–2.5 × 1–1.5 cm;
peduncles 1–10(–20) mm.
ovoid, 1.2–2.8 × 1.2–2.2 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 to ellipsoid, 2.5–5 mm, apex rounded;
stalks 1–3 mm;
scales 2–3, subequal, often poorly developed, heavily resin-coated.
before new growth in spring.
in late summer or early fall.
obovate, wings reduced to narrow, thickened ridges.
elliptic, wings reduced to narrow, leathery ridges.
= 28.
= 28.
Alnus glutinosa
Alnus maritima
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 maritima consists of widely disjunct populations in Delaware, Maryland, and southern Oklahoma. The populations probably represent remnants of Pleistocene and post-Pleistocene distributions and migrations. It is our only member of the predominantly Asian fall-blooming Alnus subg. Clethropsis.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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