Monoecious, and bearing their male flowers in catkins, they are readily distinguished from the rest of the catkin-bearing trees by their peculiar fruit, an acorn or nut, enclosed at the base in a woody cup, formed by the consolidation of numerous involucral bracts developed beneath the fertile flower, simultaneously with a cup-like expansion of the thalamus, to which the bracteal scales are more or less adherent.
The male flowers are in small clusters on the usually slender and pendent stalk, forming an interrupted catkin; the stamens vary in number, usually six to twelve.
It is characterized by its needle-leaved Coniferae, its catkin-bearing (Amentaceae) and other trees, deciduous in winter, and its profusion of herbaceous species.
To take, for example, one of the most characteristic features of the Palaearctic region, its catkin-bearing glpridiini,c frpec ~,, North Amnt4ra ~ fnA nrnrgar~, the came a-pliers as in the Old Worldoaks, chestnuts, beeches, hazels, hornbeams, birches, alders, willows and poplars.
- Catkin of Male ing pendulous anthers and pro Flowers of Hazel.
Cordaites, a tall plant (20-30 ft.) with yucca-like leaves, was related to the cycads and conifers; the catkin-like inflorescence, which bore yew-like berries, is called Cardiocarpus.
- 1, Female catkin (enlarged); 2, Pair of fruits (nuts) each enclosed in its involucre (reduced).
- Catkin of Hazel (Corylus Avellana), consisting of an axis covered with bracts in the form of scales, each of which covers a male flower, the stamens of which are seen projecting beyond the scale.
The catkin falls off entire, separating from the branch by an articulation.
A, Male flower and young cones; b, male catkin; c, d, outer and inner side of anther-scale.