Alnus glutinosa
Alnus rhombifolia
black alder, European alder, European black alder
California alder, white alder
dark brown, smooth, becoming darker and breaking into shallow fissures in age;
lenticels pale, horizontal.
light gray, smooth, becoming darker and breaking into scales 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 elliptic to rhombic, rarely ovate, 4–9 × 2–5 cm, base cuneate to rounded, margins flat, finely serrate or serrulate, sometimes slightly lobed, without noticeably larger secondary teeth, apex acute or obtuse to rounded;
surfaces abaxially sparsely pubescent to villous.
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 3–7, 3–10 cm, stamens 2, or 4 with 2 reduced in size; pistillate catkins in 1 or more clusters of 2–6.
ovoid to nearly globose, 1.2–2.5 × 1–1.5 cm;
peduncles 1–10(–20) mm.
ovoid to nearly cylindric, 1–2.2 × 0.7–1 cm;
peduncles 1–10 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, ellipsoid to obovoid, 3–9 mm, apex rounded;
stalks 3–5 mm;
scales 2, equal, valvate, sometimes incompletely covering underlying leaves, moderately to heavily resin-coated.
before new growth in spring.
before new growth in spring.
obovate, wings reduced to narrow, thickened ridges.
broadly elliptic, wings narrower than body, irregular in shape, leathery.
= 28.
Alnus glutinosa
Alnus rhombifolia
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 rhombifolia is the common alder throughout the dry Mediterranean climatic zone of coastal western United States. Mexican populations are not known, but because A. rhombifolia has been collected as far south as San Diego, California, it should be expected in adjacent Baja California.
Native Americans used various parts of Alnus rhombifolia medicinally for diarrhea, consumption, and burns, as a blood purifier, an emetic, and a wash for babies with skin diseases, and to facilitate childbirth (D. E. Moerman 1986).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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