The Birch Family
This is a family of deciduous bisexual trees and shrubs. The Betulaceae have loose bark which remains intact or exfoliates in thin layers. The bark is often marked by lenticels. Their leaves are alternate, simple, petiolate and pinnately veined. Leaf margins are usually toothed. Unisexual flower cluster form terminally or in the axils; they contain bracts. Male flowers are clustered into more or less elongate pendent catkins consisting of 1 – 3 flowers (cymules). Female flowers are formed in pendulous or erect, short catkins or in woody cones formed form the fused bracts. The small flowers are unisexual, wind pollinated and lack a perianth. The usual 4 – 12 stamens have free or basally fused filaments. The ovary is superior and consists of 2 -3 fused carpels each bearing a linear, filiform, free style. The fruits are woody cone-like or leaf-like structures with persistent or deciduous scales and the seeds are laterally compressed nuts or two-winged samaras each with a single seed.
The family is distributed across temperate and boreal forests of the Northern Hemisphere. The Betulaceae consists of 6 genera: The tribe Betuloideae – Alnus (alder), Betula (birch); and the Tribe Coryloidea – Carpinus (ironwood hornbeam), Corylus (hazelnut), Ostrya (hophornbeam) and Ostryopsis (hazel-hornbeam). Alnus and Betula are harvested for their fine-grained wood; Carpinus has been used for it hard wood in tool handles, and water and cart wheels. Betula pendula is tapped for its sweet spring sap. Corylus avellana, C. colurna and C. avellana are used for production of the hazel nut and C. maxima for the filbert. Betula is the classical Latin name for a birch tree, borrowed form the Gaulish name for it (bedwen)