Betulaceae Gray

First published in Nat. Arr. Brit. Pl. 2: 222, 243. 1822 [10 Jan 1822] (1822)nom. cons.
This family is accepted

Descriptions

Gemma Bramley, Anna Trias-Blasi & Richard Wilford (2023). The Kew Temperate Plant Families Identification Handbook. Kew Publishing Royal Botanic Gardens, Kew

Recognition
Characters of similar families: Juglandaceae: leaves compound and often aromatic, stipules absent. Fagaceae: fruits enclosed by a multi-bracteate cupule. Salicaceae: plants usually dioecious, teeth of leaves often with a spherical or papillate gland at the apex, ovary superior, fruit a berry or capsule.
Morphology General Habit
Trees and shrubs, deciduous, monoecious; bark close or exfoliating in thin layers, often with prominent lenticels
Morphology General Buds
Winter buds stalked or sessile, scaly or naked
Morphology Leaves Stipules
Stipules free, deciduous
Morphology Leaves
Leaves alternate, simple, petiolate, pinnately veined, sometimes lobulate, margin serrate to nearly entire
Morphology Reproductive morphology Inflorescences
Inflorescences terminal or lateral, unisexual, flowers much reduced
sex Male
Male catkins often precocious, pendulous, cylindric, conspicuously bracteate, consisting of crowded, 1–3-flowered clusters; stamens (1–)4–6; filaments very short; anthers 2-locular, medifixed, dehiscing by longitudinal slits, thecae connate or separate
sex Female
Female inflorescences either of erect to pendulous bracteate catkins, or of compact clusters of tiny, highly reduced flowers; gynoecium 2(–3)-carpellate; ovary inferior, usually 2-locular below, 1-locular above; placentation axile; ovules 1–2 per locule, pendulous; styles 2, linear, free
Morphology Reproductive morphology Fruits Infructescences
Infructescences cone-like with small, crowded, woody or leathery scales, these are deciduous with the fruits or persistent; or formed of clusters subtended or enclosed by large, nearly leafy bracts falling with the fruits
Morphology Reproductive morphology Fruits
Fruit a nut, nutlet, or tiny 2-winged samara
Morphology Reproductive morphology Seeds
Seed 1, endosperm present but thin at maturity, embryo straight, cotyledons flat or greatly thickened, oily.
Distribution
Six genera (Alnus, Betula, Carpinus, Corylus, Ostrya and Ostryopsis) and 150–200 species; mainly in cool temperate and boreal northernhemisphere, some on tropical mountain ranges through Central America and the Andes to Argentina, or in SE Asia. Ostryopsis is restricted to China.
Note
Deciduous trees and shrubs. Leaves simple, alternate, usually serrate. Monoecious. Flowers much reduced, in unisexual inflorescences. Male catkins pendulous, cylindric, conspicuously bracteate, often precocious. Fruit a nut, nutlet or samara.
Description Author
Saba Rokni
[KTEMP-FIH]

Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://creativecommons.org/licenses/by/3.0

Morphology General Habit
Trees
Morphology Reproductive morphology Flowers
Flowers unisexual (plants monoecious), borne on catkins, subtended by bracts; petals absent; sepals 1-6, scaly Male flowers with 2-12 stamens, anthers basifixed and dehiscing by longitudinal slits; staminodes absent. Female flowers syncarpous (2-3 carpels); styles not fused; ovary inferior with 2-3 locules
Morphology Reproductive morphology Fruits
Fruits are one-seeded nuts: flattened, winged and borne in cone-like structure (Alnus Mill.), ovoid and subtended by winged bract giving the impression of a samara (Carpinus L.) or encased in inflated bracts on a loose catkin (Ostrya Scop.).
Distribution
Only one genus, Alnus, occurs in South America.  Carpinus and Ostrya are found in Central America and Mexico, at the southern end of their ranges. Native but also sometimes cultivated.
Diagnostic
Close, ascending secondary leaf veins. Twice-toothed leaf margin (Alnus and Carpinus). Key differences from similar families: Potentially confused with other members of the Fagales but distinguishable from them by the following features: Fagaceae - fruit not subtended or partially enclosed by woody accrescence or cupule. Ticodendraceae - absence of circular stipule scar; nutlike fruit. Myricaceae - inferior ovary; absence of gland dots and peltate scales on leaves. Juglandaceae - simple leaves. Ulmaceae - The leaves are also superficially similar to Ulmaceae, but differ in having symmetrical bases. Distinguishing characters (always present): Alternatesimpleserrate or dentate -margined leaves. Unisexual flowers borne on catkins. Stipulate. Nutlike fruits. The three species are most readily distinguished by their fruits: Alnus - Small winged nuts borne in a cone-like structure (which could be confused for a single fruit dehiscing to release its seeds). Carpinus - Ovoid nuts subtended by large wing-like bracts (giving the impression of a samara), borne on an elongated pendulous inflorescence. Ostrya - ovoid nuts enclosed in inflated bracts, borne on an elongated pendulous inflorescence.
Note
Number of genera: Three genera are represented by three species in the Neotropics: Alnusacuminata Kunth (= A. jorullensis, which is sometimes regarded as a separate species), widely distributed through South and Central America between 1200 and 3200m altitude. It is generally associated with damp ground and occurs along the banks of rivers and marshes. Carpinus caroliniana Walter is a small sub-canopy tree occurring in Mexico and Central America (Guatemala and western Honduras). Ostrya virginiana (Mill.) K. Koch occurs in Mexico and Central America (to El Salvador and Honduras). Notes on delimitation: This family is placed by molecular and morphological studies in the Fagales, together with Fagaceae, Juglandaceae, Myricaceae and Ticodendraceae. All members of this family have associations with nitrogen-fixing bacteria in their roots (e.g. Frankia spp.). The wood of Alnus acuminata is very hard and is used for many purposes including construction, furniture, matches, musical instruments, and tool handles. This species is planted as a timber tree and has also been used for agroforestry in Costa Rica (as a shade tree for coffee crops).  Ostrya virginiana also produces very hard wood and has been used by native Americans for various medicinal purposes including the treatment of toothache.  Both Alnus and Ostrya have been used for tanning leather.
[NTK]

Uses

Use
Used for timber, charcoal, hazelnuts (Corylus), ornamental trees and shrubs, and soil nitrification (Alnus).
[KTEMP-FIH]

Sources

  • Kew Names and Taxonomic Backbone

    • The International Plant Names Index and World Checklist of Vascular Plants 2025. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0

  • Neotropikey

    • Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.
    • http://creativecommons.org/licenses/by-nc-sa/3.0

  • The Kew Temperate Plant Families Identification Handbook

    • The Kew Temperate Plant Families Identification Handbook
    • http://creativecommons.org/licenses/by-nc-sa/3.0