View source for Alnus

{{Treatment/ID
|accepted_name=Alnus
|accepted_authority=Miller
|publications={{Treatment/Publication
|title=Gard. Dict. Abr. ed.
|place=4. 1754
|year=1754
}}
|common_names=Alder;aulne;aune
|basionyms=
|synonyms=
|hierarchy=Betulaceae;Betulaceae subfam. Betuloideae;Alnus
|hierarchy_nav=<div class="higher-taxa"><div class="higher-taxon"><small>family</small>[[Betulaceae]]</div><div class="higher-taxon"><small>subfamily</small>[[Betulaceae subfam. Betuloideae]]</div><div class="higher-taxon"><small>genus</small>[[Alnus]]</div></div>
|etymology=Latin alnus, alder
|volume=Volume 3
|mention_page=
|treatment_page=
}}<!--

--><span class="statement" id="st-d0_s0" data-properties="whole_organism some measurement;whole_organism growth form;whole_organism some measurement;whole_organism growth form"><b>Trees </b>or shrubs, to 35 m;</span> <span class="statement" id="st-d0_s1" data-properties="trunk quantity;trunk architecture;trunk architecture">trunks usually several, branching excurrent to deliquescent.</span> <span class="statement" id="st-d0_s2" data-properties="bark coloration;bark width;bark architecture or pubescence or relief;bark arrangement"><b>Bark </b>of trunks and branches light gray to dark-brown, thin, smooth, close;</span> <span class="statement" id="st-d0_s3" data-properties="lenticel presence;lenticel coloration;lenticel prominence;lenticel size">lenticels often present, pale, prominent, sometimes horizontally expanded.</span> <span class="statement" id="st-d0_s4" data-properties="wood coloration;wood coloration;wood pubescence or texture;wood texture;exposure coloration"><b>Wood </b>nearly white, turning reddish upon exposure to air, moderately light and soft, texture fine.</span> <span class="statement" id="st-d0_s5" data-properties="twig arrangement;twig density"><b>Branches,</b> branchlets, and twigs nearly 2-ranked to diffuse;</span> <span class="statement" id="st-d0_s6" data-properties="twig life cycle;twig variability;twig variability;short-shoot length or size">young twigs uniform or (Alnus subg. Alnobetula) differentiated into long and short-shoots.</span> <span class="statement" id="st-d0_s7" data-properties="bud season;bud architecture;bud shape;bud shape;bud shape;apex shape"><b>Winter </b>buds stipitate (nearly sessile in Alnus subg. Alnobetula), narrowly to broadly ovoid or ellipsoid, terete, apex acute to rounded;</span> <span class="statement" id="st-d0_s8" data-properties="scale quantity;scale arrangement or dehiscence;scale quantity;scale arrangement;scale architecture or pubescence or relief;scale quantity">scales 2–3, valvate, or (Alnus subg. Alnobetula) several, imbricate, smooth, or (Alnus subg. Clethropsis) sometimes none.</span> <span class="statement" id="st-d0_s9" data-properties="leaf arrangement;short-shoot length or size"><b>Leaves </b>borne on long or short-shoots, 3-ranked to nearly 2-ranked.</span> <span class="statement" id="st-d0_s10" data-properties="leaf-blade shape;leaf-blade width;leaf-blade texture;base variability;base shape;margin architecture or shape;margin architecture or shape;margin architecture or shape;margin architecture or shape;margin architecture or shape;margin architecture or shape;apex variability;apex shape"><b>Leaf-</b>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;</span> <span class="statement" id="st-d0_s11" data-properties="surface pubescence;surface architecture or function or pubescence">surfaces glabrous to tomentose, abaxially sometimes resinous-glandular.</span> <span class="statement" id="st-d0_s12" data-properties="catkin architecture;catkin position;catkin arrangement;catkin arrangement;catkin arrangement;catkin prominence;catkin prominence;catkin size;season growth order;season size"><b>Inflorescences:</b> 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;</span> <span class="statement" id="st-d0_s13" data-properties="catkin architecture;catkin position;catkin architecture or arrangement or growth form;catkin architecture or arrangement or growth form;catkin orientation;catkin shape;catkin texture;catkin architecture">pistillate catkins proximal to staminate catkins, solitary or in relatively small racemose clusters, erect to nearly pendulous, ovoid to ellipsoid, firm;</span> <span class="statement" id="st-d0_s14" data-properties="scale arrangement;scale development;scale life cycle;flower arrangement;flower development;flower life cycle;catkin architecture">scales and flowers crowded, developing and maturing at same time as staminate catkins.</span> <span class="statement" id="st-d0_s15" data-properties="flower architecture;catkin quantity"><b>Staminate </b>flowers in catkins, 3 per scale;</span> <span class="statement" id="st-d0_s16" data-properties="stamen atypical quantity;stamen atypical quantity;stamen quantity">stamens (3–) 4 (–6);</span> <span class="statement" id="st-d0_s17" data-properties="anther architecture or shape;filament architecture or shape">anthers and filaments undivided.</span> <span class="statement" id="st-d0_s18" data-properties="flower architecture;flower quantity"><b>Pistillate </b>flowers usually 2 per scale.</span> <span class="statement" id="st-d0_s19" data-properties="infructescence orientation;infructescence orientation"><b>Infructescences </b>erect or pendulous;</span> <span class="statement" id="st-d0_s20" data-properties="scale length;scale size or width;scale texture;lobe quantity">scales persistent long after release of fruits, with 5 lobes, greatly thickened, woody.</span> <span class="statement" id="st-d0_s21" data-properties="samara size"><b>Fruits </b>tiny samaras, lateral wings 2, leathery or membranaceous, reduced or essentially absent in some species.</span> <span class="statement" id="st-d0_s22" data-properties="lateral wing quantity;lateral wing texture;lateral wing texture;lateral wing size;lateral wing presence;x chromosome quantity">x = 7.</span><!--

-->{{Treatment/Body
|distribution=Forested temperate and boreal Northern Hemisphere;North America;Asia
|discussion=<p>Species ca. 25 (8 species in the flora).</p><!--
--><p>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.</p><!--
--><p>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.</p>
|tables=
|references=
}}<!--

--><div class="treatment-key">
==Key==
<div class="treatment-key-group">
  
{| class="wikitable fna-keytable"
|-id=key-0-1
|1
|Winter buds nearly sessile (stalks usually not over 1 mm), covered by 4–6 unequal, imbricate scales; staminate inflorescences formed late in growing season before blooming, exposed during winter; pistillate inflorescences enclosed within buds during winter, exposed with first new growth in spring (subg. Alnobetula).
|[[Alnus viridis|Alnus viridis]]
|-id=key-0-1
|1
|Winter buds distinctly stalked, covered, sometimes incompletely, by 2–3 nearly equal, valvate scales; staminate and pistillate inflorescences both formed mid to late in growing season, not with first new growth in spring.
|[[#key-0-2| > 2]]
|-id=key-0-2
|2
|Pistillate inflorescences and infructescences solitary in leaf axils along main stems; flowering near end of growing season (subg. Clethropsis).
|[[Alnus maritima|Alnus maritima]]
|-id=key-0-2
|2
|Pistillate inflorescences (and later infructescences) on short branchlets in racemose clusters; flowering at beginning of growing season (subg. Alnus).
|[[#key-0-3| > 3]]
|-id=key-0-3
|3
|Leaf blade margins serrulate or finely serrate, without noticeably larger secondary teeth (although sometimes slightly lobulate).
|[[#key-0-4| > 4]]
|-id=key-0-3
|3
|Leaf blade margins doubly serrate or crenate, with distinctly larger secondary teeth, or coarsely serrate or serrate-dentate.
|[[#key-0-5| > 5]]
|-id=key-0-4
|4
|Leaf blade broadly elliptic to obovate, apex obtuse to rounded; staminate flowers with 4 stamens; large shrubs of e North America.
|[[Alnus serrulata|Alnus serrulata]]
|-id=key-0-4
|4
|Leaf blade narrowly elliptic to rhombic, apex acute or obtuse, usually not rounded; stamens 2, or 4 with 2 reduced in size; trees of mountainous w United States.
|[[Alnus rhombifolia|Alnus rhombifolia]]
|-id=key-0-5
|5
|Leaf blade margins strongly revolute; large trees of nw North America.
|[[Alnus rubra|Alnus rubra]]
|-id=key-0-5
|5
|Leaf blade margins flat or only slightly revolute; trees and shrubs.
|[[#key-0-6| > 6]]
|-id=key-0-6
|6
|Leaf blade narrowly ovate or lanceolate to narrowly elliptic; major teeth sharp, acuminate; trees of mountainous s Arizona and New Mexico, adjacent nw Mexico.
|[[Alnus oblongifolia|Alnus oblongifolia]]
|-id=key-0-6
|6
|Leaf blade ovate, elliptic, obovate, or nearly orbiculate; major teeth acute to obtuse or rounded.
|[[#key-0-7| > 7]]
|-id=key-0-7
|7
|Leaf blade obovate to ±orbiculate, apex rounded to retuse or obcordate; moderately large introduced trees naturalized in ne United States, adjacent Canada.
|[[Alnus glutinosa|Alnus glutinosa]]
|-id=key-0-7
|7
|Leaf blade ovate to elliptic, apex acute to obtuse; native shrubs or shrubby trees.
|[[Alnus incana|Alnus incana]]
|}
</div></div><!--

-->{{#Taxon:
name=Alnus
|authority=Miller
|rank=genus
|parent rank=subfamily
|synonyms=
|basionyms=
|family=Betulaceae
|distribution=Forested temperate and boreal Northern Hemisphere;North America;Asia
|reference=None
|publication title=Gard. Dict. Abr. ed.
|publication year=1754
|special status=
|source xml=https://bibilujan@bitbucket.org/aafc-mbb/fna-fine-grained-xml.git/src/84153f6d59a0a91d69695978a64cee7560374f8e/V3/V3_953.xml
|subfamily=Betulaceae subfam. Betuloideae
|genus=Alnus
|anther architecture or shape=undivided
|apex shape=acute;obtuse or acuminate
|apex variability=variable
|bark architecture or pubescence or relief=smooth
|bark arrangement=close
|bark coloration=light gray;dark-brown
|bark width=thin
|base shape=cuneate;rounded
|base variability=variable
|bud architecture=stipitate
|bud season=winter
|bud shape=terete;ellipsoid;ovoid
|catkin architecture=staminate;staminate;pistillate;staminate
|catkin architecture or arrangement or growth form=in relatively small racemose clusters;solitary
|catkin arrangement=solitary;cluster;racemose
|catkin orientation=erect;nearly pendulous
|catkin position=proximal;lateral
|catkin prominence=enclosed in buds;exposed
|catkin quantity=3
|catkin shape=ovoid;ellipsoid
|catkin size=expanding
|catkin texture=firm
|exposure coloration=reddish
|filament architecture or shape=undivided
|flower architecture=pistillate;staminate
|flower arrangement=crowded
|flower development=developing
|flower life cycle=maturing
|flower quantity=2
|infructescence orientation=pendulous;erect
|lateral wing presence=absent
|lateral wing quantity=2
|lateral wing size=reduced
|lateral wing texture=membranaceous;leathery
|leaf arrangement=3-ranked;nearly 2-ranked
|leaf-blade shape=ovate;elliptic or obovate
|leaf-blade texture=leathery
|leaf-blade width=thin
|lenticel coloration=pale
|lenticel presence=absent
|lenticel prominence=prominent
|lenticel size=expanded
|lobe quantity=5
|margin architecture or shape=entire;serrulate;entire;serrulate;serrate;serrate
|samara size=tiny
|scale architecture or pubescence or relief=smooth
|scale arrangement=crowded;imbricate
|scale arrangement or dehiscence=valvate
|scale development=developing
|scale length=persistent
|scale life cycle=maturing
|scale quantity=0;several;2;3
|scale size or width=thickened
|scale texture=woody
|season growth order=previous
|season size=expanding
|short-shoot length or size=long;long
|stamen atypical quantity=4;6
|stamen quantity=4
|surface architecture or function or pubescence=resinous-glandular
|surface pubescence=glabrous;tomentose
|trunk architecture=excurrent;deliquescent
|trunk quantity=several
|twig arrangement=2-ranked
|twig density=diffuse
|twig life cycle=young
|twig variability=differentiated;uniform
|whole_organism growth form=shrub;tree
|whole_organism some measurement=0m;35m
|wood coloration=light;white
|wood pubescence or texture=soft
|wood texture=fine
|x chromosome quantity=7
}}<!--

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