Corylus: A plant genus of the family BETULACEAE known for the edible nuts.Betulaceae: A plant family of the order Fagales, subclass Hamamelidae, class Magnoliopsida. They have simple, serrate, alternate leaves. Male flowers are borne in long, pendulous catkins; the female in shorter, pendulous or erect catkins. The fruit is usually a small nut or a short-winged samara.Alnus: A plant genus of the family BETULACEAE that is distinguished from birch (BETULA) by its usually stalked winter buds and by cones that remain on the branches after the small, winged nutlets are released.Betula: A plant genus of the family BETULACEAE. The tree has smooth, resinous, varicolored or white bark, marked by horizontal pores (lenticels), which usually peels horizontally in thin sheets.Pollen: The fertilizing element of plants that contains the male GAMETOPHYTES.