Order 103. CUPULÌFERÆ. (Oak Family.)
Monœcious trees or shrubs, with alternate simple straight-veined leaves, deciduous stipules, the sterile flowers in catkins (or capitate-clustered in the Beech), the fertile solitary, clustered, spiked, or in scaly catkins, the 1-celled and 1-seeded nut with or without an involucre. Ovary more or less 2–7-celled, with 1 or 2 pendulous anatropous ovules in each cell; but all the cells and ovules except one disappearing in the fruit. Seed with no albumen, filled with the embryo.
Tribe I. BETULEÆ. Flowers in scaly catkins, 2 or 3 to each bract. Sterile catkins pendulous. Stamens 2–4, and calyx usually 2–4-parted. Fertile flowers with no calyx, and no involucre to the compressed and often winged small nut. Ovary 2-celled, 2-ovuled.
1. Betula. Stamens 2, bifid. Fertile scales thin, 3-lobed, deciduous with the nuts.
2. Alnus. Stamens 4. Fertile scales thick, entire, persisting after the nuts have fallen.
Tribe II. CORYLEÆ. Sterile catkins pendulous, with no calyx; stamens 3 or more to each bract and more or less adnate to it, the filaments often forked (anthers 1-celled). Fertile flowers in a short ament or head, 2 to each bract, and each with one or more bractlets which form a foliaceous involucre to the nut. Ovary 2-celled, 2-ovuled.
[*] Bract of staminate flower furnished with a pair of bractlets inside; fertile flowers few.
3. Corylus. Involucre leafy-coriaceous, enclosing the large bony nut.
[*][*] Bract of staminate flower simple; fertile flowers in short catkins; nut small, achene-like.
4. Ostrya. Each ovary and nut included in a bladdery and closed bag.