Skip Navigation
Sign In
  • Home
  • Search
    • Search Collections
    • Map Search
  • Chicago Botanic Garden
    • Project Information
    • Checklists
    • Create a Checklist
    • Dynamic Key
  • Denver Botanic Gardens
    • Project Information
    • Checklists
    • Create a Checklist
    • Dynamic Key
  • Desert Botanical Garden
    • Project Information
    • Checklists
    • Create a Checklist
    • Dynamic Key
  • NY Botanical Garden
    • Project Information
    • Checklists
    • Create a Checklist
    • Dynamic Key
  • Marie Selby Botanical Gardens
    • Project Information
    • Checklists
    • Create a Checklist
    • Dynamic Key
  • Sitemap

Alnus

Alnus
Family: Betulaceae
Alnus image
Max Licher
  • FNA
  • VPAP
  • Gleason & Cronquist
  • Resources
John J. Furlow in Flora of North America (vol. 3)
Trees or shrubs , to 35 m; trunks usually several, branching excurrent to deliquescent. Bark of trunks and branches light gray to dark brown, thin, smooth, close; lenticels often present, pale, prominent, sometimes horizontally expanded. Wood nearly white, turning reddish upon exposure to air, moderately light and soft, texture fine. Branches, branchlets, and twigs nearly 2-ranked to diffuse; young twigs uniform or ( Alnus subg. Alnobetula ) differentiated into long and short shoots. Winter buds stipitate (nearly sessile in Alnus subg. Alnobetula ), narrowly to broadly ovoid or ellipsoid, terete, apex acute to rounded; scales 2--3, valvate, or ( Alnus subg. Alnobetula ) several, imbricate, smooth, or ( Alnus subg. Clethropsis ) sometimes none. Leaves borne on long or short shoots, 3-ranked to nearly 2-ranked. Leaf blade ovate to elliptic or obovate, thin to leathery, base variable, cuneate to rounded, margins doubly serrate, serrate, serrulate, or nearly entire, apex variable, acute to obtuse or acuminate to rounded; surfaces glabrous to tomentose, abaxially sometimes resinous-glandular. Inflorescences: staminate catkins lateral, in racemose clusters or ( Alnus subg. Clethropsis ) solitary, formed ( Alnus subg. Alnus and Clethropsis ) during previous growing season and exposed or enclosed in buds during winter, or ( Alnus subg. Clethropsis ) formed and expanding during same growing season, expanding before or with leaves; pistillate catkins proximal to staminate catkins, solitary or in relatively small racemose clusters, erect to nearly pendulous, ovoid to ellipsoid, firm; scales and flowers crowded, developing and maturing at same time as staminate catkins. Staminate flowers in catkins, 3 per scale; stamens (3--)4(--6); anthers and filaments undivided. Pistillate flowers usually 2 per scale. Infructescences erect or pendulous; scales persistent long after release of fruits, with 5 lobes, greatly thickened, woody. Fruits tiny samaras, lateral wings 2, leathery or membranaceous, reduced or essentially absent in some species. x = 7.

Alders resemble birches but are easily distinguished from them by the infructescences, which consist of persistent, 5-lobed, woody scales (versus deciduous, 3-lobed, thin scales). Except in members of Alnus subg. Alnobetula Petermann (which have nearly sessile buds with several imbricate scales), alders are also distinctive in their stipitate buds bearing two stipular scales. The fruits, borne two to a scale, are laterally winged, although the wings are sometimes reduced or absent.

The genus is diverse, including several very distinct lines of specialization. The shrubby or arborescent Alnus subg. Alnus is characterized by winter buds with long stalks and two valvate scales, inflorescences borne in racemose clusters, and development of both pistillate and staminate inflorescences during the growing season prior to anthesis, with these fully exposed during winter. It includes the common A . rubra , A . incana , A . oblongifolia , and A . serrulata . Alnus subg. Alnobetula (represented in North America by three subspecies of A . viridis ) consists of shrubby species of cold-climate regions. In this group, the buds are nearly sessile and covered by several imbricate scales. Both staminate and pistillate catkins are formed the season before anthesis, but only the staminate ones are exposed during winter. The predominantly Asian Alnus subg. Clethropsis (Spach) Regel is represented in America by a single species, A . maritima , a small tree or large shrub of stream banks, marshes, and the shores of shallow lakes. Members of this group are unique in that they bloom in autumn rather than spring. They also differ from other native species in Alnus in having essentially naked buds, leaves with semicraspedodromous venation (i.e., with the secondary veins branching and anastomosing with each other near the margin before reaching the teeth), and solitary pistillate inflorescences borne in the axils of foliage leaves. All of the alders associate symbiotically with species of the actinomycete Frankia , leading to the formation of nodules on the roots of the plants and the fixation of atmospheric nitrogen.

JANAS 33(1)
INFLORESCENCE: in ours formed the previous growing season and exposed during winter; catkins 1-several in racemose clusters; pistillate catkins erect or pendulous, in age becoming cone-like with thick, woody, 5-lobed scales that persist long after fruits fall. PLANT: Trees or shrubs to 35 m tall; stems often bearing lenticels; twigs 2-ranked or diffuse, uniform or differentiated into long and short shoots; winter buds stipitate, bearing 2-3 stipular scales. LEAVES: on long or short shoots, 3-ranked to nearly 2-ranked; blades ovate to elliptic or obovate; margins serrate, doubly serrate, or sub-entire; surfaces glabrous to tomentose, sometimes resinous-glandular abaxially. STAMINATE FLOWERS: 3 per scale, each with (1-)2-4(-6) stamens. PISTILLATE FLOWERS: usually 2 per scale. FRUITS: tiny leathery samaras; lateral wings 2, sometimes reduced or essentially absent. x = 7. NOTES: Ca. 25 spp.; mostly n hemisphere (Latin: alnus = alder). Furlow, J. J. 1979. Rhodora 81:1-121, 151-248. All alders harbor species of the nitrogen-fixing actinomycete genus Frankia in root nodules. REFERENCES: Brasher, Jeffrey W. 2001. Betulaceae. J. Ariz. - Nev. Acad. Sci. Volume 33(1)
Vascular plants of NE US and adjacent Canada
Staminate catkins pendulous, usually clustered, each bract subtending 3 fls with minute, 4-parted cal and 4 stamens with short, undivided filaments; pistillate catkins becoming woody, long-persistent, short, ovoid to ellipsoid or short-cylindric, each bract subtending 2 fls without cal; bracts of the pistillate catkins adnate to the bractlets, the compound unit cuneate, rounded or truncate and lobed at the summit; fr a small achene or samara, crowned with the 2 short, persistent styles and surrounded by a thin margin or membranous wing; trees or shrubs with 3-angled pith and broad, ovate to obovate, deciduous lvs. 30, mostly N. Hemisphere.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.
Species within checklist: Old Fort Lewis Property - Hesperus, La Plata Co, CO || << 1 - 50 taxa >>
Alnus acuminata
Media resource of Alnus acuminata
Map not
Available
Alnus alnobetula
Media resource of Alnus alnobetula
Map not
Available
Alnus alnus
Media resource of Alnus alnus
Map not
Available
Alnus arguta
Media resource of Alnus arguta
Map not
Available
Alnus cordata
Media resource of Alnus cordata
Map not
Available
Alnus cremastogyne
Media resource of Alnus cremastogyne
Map not
Available
Alnus crispa
Media resource of Alnus crispa
Map not
Available
Alnus densiflora
Media resource of Alnus densiflora
Map not
Available
Alnus elliptica
Media
not available
Map not
Available
Alnus fallacina
Media resource of Alnus fallacina
Map not
Available
Alnus fauriei
Media resource of Alnus fauriei
Map not
Available
Alnus ferruginea
Media resource of Alnus ferruginea
Map not
Available
Alnus firma
Media resource of Alnus firma
Map not
Available
Alnus firmifolia
Media resource of Alnus firmifolia
Map not
Available
Alnus formosana
Media resource of Alnus formosana
Map not
Available
Alnus glabrata
Media resource of Alnus glabrata
Map not
Available
Alnus glauca
Media
not available
Map not
Available
Alnus glutinosa
Media resource of Alnus glutinosa
Map not
Available
Alnus henryi
Media
not available
Map not
Available
Alnus hirsuta
Media resource of Alnus hirsuta
Map not
Available
Alnus hybrida
Media resource of Alnus hybrida
Map not
Available
Alnus incana
Media resource of Alnus incana
Map not
Available
Alnus inokumai
Media resource of Alnus inokumai
Map not
Available
Alnus japonica
Media resource of Alnus japonica
Map not
Available
Alnus jorullenis
Media resource of Alnus jorullenis
Map not
Available
Alnus jorullensis
Media resource of Alnus jorullensis
Map not
Available
Alnus mandshurica
Media resource of Alnus mandshurica
Map not
Available
Alnus maritima
Media resource of Alnus maritima
Map not
Available
Alnus matsumurae
Media resource of Alnus matsumurae
Map not
Available
Alnus maximowiczii
Media resource of Alnus maximowiczii
Map not
Available
Alnus metoporina
Media resource of Alnus metoporina
Map not
Available
Alnus mollis
Media resource of Alnus mollis
Map not
Available
Alnus nepalensis
Media resource of Alnus nepalensis
Map not
Available
Alnus nitida
Media resource of Alnus nitida
Map not
Available
Alnus noveboracensis
Media resource of Alnus noveboracensis
Map not
Available
Alnus oblongifolia
Media resource of Alnus oblongifolia
Map not
Available
Alnus oregona
Media resource of Alnus oregona
Map not
Available
Alnus orientalis
Media resource of Alnus orientalis
Map not
Available
Alnus pendula
Media resource of Alnus pendula
Map not
Available
Alnus pringlei
Media resource of Alnus pringlei
Map not
Available
Alnus pubescens
Media resource of Alnus pubescens
Map not
Available
Alnus rhombifolia
Media resource of Alnus rhombifolia
Map not
Available
Alnus rubra
Media resource of Alnus rubra
Map not
Available
Alnus rugosa
Media resource of Alnus rugosa
Map not
Available
Alnus serrulata
Media resource of Alnus serrulata
Map not
Available
Alnus serrulatoides
Media resource of Alnus serrulatoides
Map not
Available
Alnus sieboldiana
Media resource of Alnus sieboldiana
Map not
Available
Alnus sinuata
Media resource of Alnus sinuata
Map not
Available
Alnus sitchensis
Media resource of Alnus sitchensis
Map not
Available
Alnus subcordata
Media
not available
Map not
Available
Institute for Museum and Library Services KU BI Logo Logo for the Biodiversity Knowledge Integration Center

This project was made possible in part by the Institute of Museum and Library Services [MG-70-19-0057-19].

EcoFlora is part of the SEINet Portal Network. Learn more here.

Powered by Symbiota.