deciduous, monoecious. Stipules present, free
, often deciduous, rarely persistent
. Leaves alternate, simple
, usually doubly serrate, rarely simply serrate, lobulate
, or entire; veins pinnate. Flowers unisexual
. Male inflorescence precocious
, pendulous, with numerous
overlapping bracts; each bract usually subtending
a small dichasium with 1-3 male flowers; stamens as many as and opposite sepals or, if sepals obsolete
, then stamens of inflorescence to 20; filaments
very short, connate
or nearly so; anthers
2-loculed, thecae connate or separate, opening by longitudinal
slits. Female inflorescence pendulous or erect
, with numerous overlapping bracts; each bract subtending a small dichasium with 2 or 3 flowers; calyx with 1-6 scalelike lobes
, or obsolete; petals absent; ovary inferior, 2-loculed; styles 2, free; ovules 2, or 1 by abortion
, pendulous from near apex of each locule. Fruit a nut or nutlet
or not. Seed 1, with straight embryo and flat or thickened cotyledons, without endosperm.
Six genera and 150-200 species: mainly in Asia, Europe, and North and South America; six genera (one endemic) and 89 species (56 endemic) in China.
Because of evolutionary divergence within the Betulaceae, the family has often been divided into tribes (i.e. , Betuleae, Carpineae, and Coryleae) or more recently into subfamilies (J. J. Furlow, J. Arnold Arbor . 71: 1-67. 1990) .
, to 35 m
usually several, branching excurrent to deliquescent. Bark
of trunks and branches light gray to dark brown, thin, smooth
, close; lenticels
often present, pale
, 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
(nearly sessile in Alnus subg. Alnobetula ), narrowly to broadly ovoid
, apex acute to rounded
, 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
, 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
, abaxially sometimes resinous-glandular. Inflorescences: staminate
, 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
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
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
Species ca. 25 (8 sp: forested temperate and boreal Northern Hemisphere; North America; Asia.
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.
- Whittaker & Margulis,1978
- Haeckel, 1866
- Cavalier-Smith, 1981
- Sinnott, 1935 ex Cavalier-Smith, 1998
- Vascular Plants
- Kenrick & Crane, 1997
- Brongniart, 1843
- Takhtajan, 1967
- Superorder: Faganae () - (Engler, 1892) Takhtajan, 1997
- Subclass: Rosidae () - Takhtajan, 1967
- Class: Spermatopsida () - Brongniart, 1843
- Infraphylum: Radiatopses () - Kenrick & Crane, 1997
- Subphylum: Euphyllophytina ()
- Phylum: Tracheophyta () - Sinnott, 1935 ex Cavalier-Smith, 1998 - Vascular Plants
- Subkingdom: Viridaeplantae () - Cavalier-Smith, 1981
- Kingdom: Plantae () - Haeckel, 1866 - Plants
Publishing author : T.G.Nitzelius Publication : in Lustgarden 57: 108 (1976) .
Members of the genus Alnus
ZipcodeZoo has pages for 28 species, subspecies, varieties, forms, and cultivars in this genus:
A. acuminata (Alder) · A. acuminata glabrata (Mexican Alder) · A. cordata (Italian Alder) · A. fallacina (Alder) · A. glutinosa (Black Alder) · A. glutinosa glutinosa (European Black Alder) · A. glutinosa 'Imperialis' (Black Alder) · A. glutinosa 'Pyramidalis' (Black Alder) · A. hirsuta (Manchurian Alder) · A. incana (Gray Alder) · A. incana incana (Speckled Alder) · A. incana rugosa (Gray Alder) · A. incana tenuifolia (Gray Alder) · A. japonica (Japanese Alder) · A. maritima (Seaside Alder) · A. nepalensis (Indian Alder) · A. nitida (West Himalayan Alder) · A. oblongifolia (Arizona Alder) · A. rhombifolia (Alder) · A. rubra (Oregon Alder) · A. rubra f. pinnatisecta (Oregon Alder) · A. serrulata (Alder) · A. viridis (Green Alder) · A. viridis crispa (Green Alder) · A. viridis fruticosa (Green Alder) · A. viridis sinuata (Green Alder) · A. viridis viridis (European Green Alder) · A. x fallacina (Alder)
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- Li Pei-chun & Cheng Sze-hsu. 1979. Betulaceae. In: Kuang Ko-zen & Li Pei-chun, eds., Fl. Reipubl. Popularis Sin. 21: 44-137.
- Furlow, J. J. 1979. The systematics of the American species of Alnus (Betulaceae). Rhodora 81: 1--121, 151--248.
- Hylander, N. 1957. On cut-leaved and small-leaved forms of Alnus glutinosa and A. incana. Svensk Bot. Tidskr. 51: 437--453.
- Murai, S. 1964. Phytotaxonomical and geobotanical studies on gen. Alnus in Japan (III). Taxonomy of whole world species and distribution of each sect. Bull. Gov. Forest Exp. Sta. 171: 1--107.
- Trappe, J. M., J. F. Franklin, R. F. Tarrant, and G. M. Hansen, eds. 1968. Biology of Alder.... Portland.
- Brands, S.J. (comp.) 1989-present. The Taxonomicon. Universal Taxonomic Services, Zwaag, The Netherlands. Accessed January 10, 2012.
- Zipcode Zoo Species Identifier: 4590624