Alnus
a genus of plants belonging to the order betulaceæ (birch-worts).
The flowers are monœceous and amentaceous. In the barren ones the scale of the catkin is three-lobed, with three flowers; the perianth is four partite; the stamina, four. In those which are fertile the scale of the catkin is subtrifid with three flowers, and there is no perianth. The ovary is two-celled, twoovuled, but only one ovule reaches perfection.