Introduction to the Betulaceae

General Description:

Classification:

Dicot -> Magnoliophyta -> Magnoliopsida -> Hamamelidae -> Fagales -> Betulaceae

• small family of only 6 genera, 120-170 species
• usually split into 2 subfamilies: Betuloideae and Coryloideae
• some botanists have made the Coryloideae a separate family, Corylaceae
• formerly lumped together with all other catkin-bearing plants into one family called Amentiferae: catkin = ament. Most former Amentiferae are now in Hamamelidae, others are in the Dilleniidae; this provides an interesting example of apparent parallel evolution of this unique inflorescence structure.

Distribution:

Cool temperate regions of N. Hemisphere, extending S. in mountains to Andes of S. America. Associated with wet areas and close to bodies of water. [Map]

History & Economic Importance:

• Food: birch syrup (Betula spp.), hazel nuts and filberts (Corylus spp.), birch beer (Betula spp.)
• Native American: birch bark canoes (Betula paperyfera)
• Allergies: Some people experience contact dermatitis from Betula
• Lumber: used in fine furniture and veneer industries
• Horticulture: shade trees, nut trees

Vegetative & Reproductive Features:

* Red text indicates diagnostic or distinctive features

• Plant
  • shrubs or trees
  • monoecious
  • wind-pollinated
  • inflorescences determinate
• Leaves
  • alternate
  • simple, serrate
  • stipulate
• Staminate Inflorescence
  • pendulous spike-like or raceme-like catkin of 2-3 flowered cymules subtended by scale-like bractlets [Example]
  • imperfect, regular
  • sepals 2-4 (-6), distinct (absent)
  • apetalous
  • stamens 2-6 (-8), distinct or filaments basally connate
• Pistillate Inflorescence
  • spike-like or head-like catkin of very reduced flowers in 1-3 flowered cymules subtended by scale-like bractlets
  • imperfect, regular
  • sepals 2-4, very reduced, connate and adnate to ovary, or absent
  • apetalous
  • carpels 2, connate
  • ovary inferior (epigynous) (superior)
  • 1-loculed at apex, 2-loculed at base with 1 axile ovule per locule
  • styles 2
• Fruit
  • nut, nutlet, or samara subtended by bractlets
  • subtending bractlets play differing, but substantial roles in fruit dispersal; fruits may be dispersed by wind (Betula), animals (e.g., Corylus), or water (some Alnus)

Distinguishing Betulaceae from other former Amentiferae

As with many families, you have to look at the combined characteristics to be certain of your identification:

• monoecious
• inflorescences determinate
• leaves simple, serrate, stipulate
• pendulous catkins of cymules subtended by scale-like bractlets
• reduced perianth
• carpels 2
• inferior epigynous ovary, 1-loculed on top, 2-loculed at base
• nut, nutlet or samara subtended by bractlets

Resources for Further Exploration

Internet:

• Families of Flowering Plants: Betulaceae from the DELTA (DEscription Language for TAxonomy) project
• Flowering Plant Gateway: Betulaceae
• The Herb Hunters Guide: Sweet Birch
• The Herb Hunters Guide: Hazel Alder
• Hophornbeam

Glossary

ament

Another name for catkin.

catkin

A spike-like or raceme-like inflorescence of apetalous staminate or pistillate flowers, often with scale bracts and wind pollinated. Often lax and drooping.

cymule

A very small, condensed cyme.

pistillate inflorescence

Having one or more pistils but no functional stamens, i.e., has a gynoecium, but no androecium.

staminate inflorescence

Having one or more stamens but no functional pistils, i.e., has a androecium, but no gynoecium.

Botanical Illustration of Betulaceae