Alnus

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Alnus Mill.

Kingdom	Plantae	Plants, but not fungi, lichens, or algae
Subkingdom	Tracheobionta	Vascular plants—plants with a “circulatory system” for delivering water and nutrients
Division	Magnoliophyta	Flowering plants, also known as angiosperms
Class	Magnoliopsida	Dicotyledons—plants with two initial seed leaves
Subclass	Rosidae	Roses, legumes, proteas, dogwoods, hydrangeas, mistletoes, euphorbias, grapes, many more
Order	Fagales	Birch, she-oak, beech, walnut, bayberry, others
Family	Betulaceae	Birch family: birches, alders, hazels, hornbeams and hop-hornbeams
Genus	Alnus	The classical Latin name for this genus

About plant names...

The Alnus genus consists of alder trees, of which there are about 30 species. Alders are members of the birch family. Most are small or medium-sized trees with multiple trunks and branches, often appearing as tall woody shrubs. Their small cone-like fruits, which remain on the trees throughout the winter, are their most recognizable feature.

This table compares some of the common species.

Alder (Alnus) · 9/11/2010 · Nashua River Rail Trail, Groton Center, Groton, Massachusetts
≈ 5 × 4" (13 × 10 cm) Species not yet identified

	*Alnus incana ssp. rugosa*	*Alnus serrulata*	*Alnus viridis*
Common Name	speckled alder	smooth alder	green alder
Flowers	Male flowers 2½-5" (6.3-12 cm) long, hanging downward; female flowers about ½" (1.3 cm) around	Bright yellow in spring, make catkins green-brown, female flowers about ½" (1.3 cm)	Male flowers about 2" (5 cm), female flowers point up, about ½" (1.3 cm)
Leaves	Oval-shaped, 2½-5" (6.3-12 cm) long, 2-4" (5-10 cm) wide	Measure(2-4"), rounded edges or small serrations, dark green above, paler and with fine hairs below	Relatively large serrations
Stem	Speckled with lenticles—horizontal lens-shaped spots	Bark is smooth, does not have lenticles	Has diamond-shaped patches
Seeds	Small cones, about ⅝" (1.6 cm), on short stalks	Small cones, about ⅝" (1.6 cm), on long thin stalks	On short stalks
Range/ Zones
Habitats	Moist areas, bordering streams, lakes and rivers; bogs and nutrient-rich swamps.
Type	Wild	Wild	Wild

Online References:

Alnus on Flora of North America (technical description)

Alnus on Wikipedia

References:

Sibley, David Allen, The Sibley Guide to Trees, Alfred A. Knopf, 2009, pp. 159-165

Little, Elbert L., National Audubon Society Field Guide to North American Trees, Eastern Region, Alfred A. Knopf, 1980

Alnus description by Thomas H. Kent, last updated 16 Sep 2020.

Green alder (Alnus viridis) · 9/20/2009 · Acadia National Park, Bar Harbor, Maine
≈ 4½ × 3" (11 × 7.9 cm) ID is uncertain

Range:

About this map...