Information is from Vascular Plant Families, James Payne Smith, Jr., Mad River Press, and Plants of the Chicago Region, Floyd Swink and Gerould Wilhelm, Indiana Academy of Science. Images and text from Dr. Gerald D. Carr, Professor, University of Hawaii at Manoa -- material for educational use from the CD: Botany online - The Internet Hypertextbook (http://www.rrz.uni-hamburg.de/biologie/b_online/). - .
Family Overview - The Fagales
Betulaceae - the Birch Family
Diversity and Distribution: The Betulaceae are monoecious trees and shrubs comprising 6 genera and 120 species. The leaves are alternate and simple; the stipules are often deciduous. The male inflorescences are pendulous catkins composed of aggregations of variously simplified 3-flowered cymes, each with a subtending bract and varying numbers of bractlets and 2-18 stamens. A 1-6-parted minute calyx is often present in each flower. The female inflorescences are conelike, erect or pendulous aggregations of 2-3-flowered cymes, each with a subtending bract and varying numbers of bractlets. Each female flower has a single compound 2-carpelled pistil with 2 deeply divided styles and an inferior or nude ovary. A placental septum divides the lower part of the ovary into 2 locules, each containing 2 ovules. The fruit is a 1-seeded indehiscent nut or samara.
In the Chicago region, the native representatives belong to the genus Betula - birch, Alnus - alder, Corylus - hazelnut, Ostrya - ironwood or hop hornbeam, and Carpinus - blue beech or musclewood. All of these are important components of local woodlands, and most form ectomycorrhizal relationships with fungi. Alder roots also associate with Frankia, nitrogen-fixing bacteria.
Floral structure:
Significant features: Catkin-bearing trees and shrubs with simple serrate leaves. Flowers with a bicarpellate inferior ovary. The fruits are nuts (e.g., hazelnut) or samaras.
Click on image for full size photo of Alder flowers.Alnus, alder. Small pinkish cone-like, female inflorescences in upper part of photo; note the deeply parted pink styles, green bracts hide the ovaries of the female flowers. Below are the pendulous catkins of male flowers. The close view of part of a male inflorescence shows the cymose clustering of male flowers.
The photo below is of a birch.
