Fagaceae : The Fagaceae family (or Fagaceae) includes plants dicotyledons ; it includes about 900 species divided into 7 to 9 genera, the best known being:
– Castanea (chestnut);
– Fagus (beech);
– Quercus (oak).
The oaks, beeches and chestnut trees provide wood for construction and furniture. The chestnut tree also has edible fruits. Oaks and chestnut trees are rich in tannins.
The oldest fossils of Fagaceae date from the Cretaceous, 90 million years ago, hence the persistence in this family of archaic traits (type 2 or 3 flowers, fertilization of the pollen tube from the side or base, wood with scalariform perforations).
These are trees or, more rarely, shrubs that dominate the deciduous forests that cover, or used to cover, vast mid-latitude regions of the Northern Hemisphere, and, to a lesser extent, regions of the Southern Hemisphere. They are found on all continents, except in tropical and southern Africa. Among the fagaceae, in temperate regions, there are beeches (Fagus), oaks (Quercus) and chestnuts (Castanea). This family represents a biomass almost comparable to that of conifers.
These plants have deciduous or evergreen foliage. Their pinnately venated leaves are generally simple, alternate (sometimes pseudo-whorled in Cyclobalanopsis), with an entire or pinnate blade and a plain or tight-toothed edge, with deciduous triangular stipules. The roots frequently form ectomycorrhizae with fungus at hyphae.
Their determinate inflorescence is varied: erect spike, hanging catkin, capituliform fascicle, even solitary, axillary or terminal actinomorphic flower. Generally, they are strict monoecious plants, the staminate flowers being in complete or reduced biparous cymes and associated with a bract, the flowers pistillate in groups of 1-5, associated with a scaly cupule3.
The staminate flowers usually have 6 (from 3 to 12) small scaly-shaped sepals, free or connate and imbricated, and 3-40 free stamens, with bilocular anthers dehiscing by longitudinal slits releasing tricolporate or tricolpate pollen grains, and sometimes a pistillode (vestigial pistil). The pistillate flowers generally have 6 (from 4 to 6) rudimentary sepals, free or connate, and an inferior ovary consisting of 3 (or even 6 and up to 12) independent carpels, each containing 2 pendulous ovules per cell (all aborting except one ), with axile placentation2.
The fruits are nuts monosperms (1 to 5) wrapped in cups woody, with four or without valves. These cupules bear on their external surface various appendages resulting from the transformation of bracts (scales of oak acorns, branched spines of chestnut bugs). Exalbuminated seeds have a straight embryo.