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Black alder is monoecious and produces separate male (staminate) and female (pistillate) florets on the same tree, both partially formed in the season before they bloom and overwintering before they become fertile. Male catkins occur in clusters of 2-5 reddish-yellow catkins, each 2-3" long when mature, narrowly cylindrical, and drooping. Male florets occur in clusters of 3-6 along the catkins, partially hidden by oval, brown bractlets. Each male floret consists of a four-lobed calyx and four stamens; petals are absent. The female florets are produced in sparse, open, branched clusters of reddish cone-like catkins, each initially about 1/4" long but growing to 3/4-1" long and 1/2" across. Within each female cone, female florets occur in clusters of 2-3, partially hidden by bractlets. Each female floret consists of a naked ovary with a pair of tiny styles at its tip that are wind pollinated. After fertilization, the male catkins wither; the bractlets of the female catkins become brown and woody, producing a very pine-like cone with the seeds nestled beneath the bractlets. The egg-shaped, flattened seeds are formally samaras, but the wing is reduced to narrow ridges. The female cones can persist through the winter.

Alnus

Alnus glutinosa

black alder [Blooms: Mar-Apr]