Hazel Alder (MatBio: TREES & SHRUBS - Matanzas Biodiversity)

Hazel Alder

Alnus serrulata

Summary ⁷

Alnus serrulata, the hazel alder or smooth alder, is a thicket-forming shrub in the family Betulaceae. It is native to eastern North America and can be found found from western Nova Scotia and southern New Brunswick south to Florida and Texas.

Description ⁸

This shrub is 5-20' tall, forming multiple trunks and a densely branched crown that is often more broad than tall. Individual trunks are up to 4" across, gray to grayish brown, and relatively smooth; they lack conspicuous lenticels. Smaller branches and twigs are gray to light brown, smooth, and terete; young twigs are often pubescent, but they become glabrous with age. Young shoots are light green, terete, and pubescent. Alternate leaves occur along the young twigs and shoots. These leaves are 2-5" long and 1¼-3½" across; they are obovate or broadly elliptic in shape, while their margins are finely serrated and often slightly wavy. The upper leaf surface is medium to dark green and glabrous, while the lower leaf surface is medium green and glabrous to sparsely pubescent. When pubescence occurs on the lower leaf surface, it is usually concentrated along the central vein. Leaf venation is pinnate with 8 or more pairs of lateral veins that are relatively straight. The petioles are ¼-1" long, light green, and pubescent. This shrub is dioecious, producing male (staminate) and female (pistillate) flowers on separate catkins. Immature catkins are present during the fall and persist through the winter in a dormant state. During the blooming period, drooping male catkins occur in clusters of 2-5 near the tips of the branches. The male catkins are 2-4" long, narrowly cylindrical in shape, and brownish yellow. Each flower male consists of a lobed calyx and stamens (about 4), but lacks petals. Several male flowers are grouped together behind each floral scale of the male catkin. The female catkins occur in clusters of 2-5 at the tips of twigs, where they are usually more or less erect. During the blooming period, each female catkin is about ¼" long and either red or purple. Each female flower consists of a naked ovary with a pair of styles; it has neither petals nor a significant calyx. A few female flowers are grouped together behind each floral scale of the female catkin. The blooming period occurs during early to mid-spring before the vernal leaves develop. The catkins are cross-pollinated by the wind. Afterwards, the female catkins become cone-like fruits about ½-¾" long, and their scales become dark brown and woody. At the base of each scale, there is a single nutlet about 2-3 mm. long that is obovoid in shape, flattened, and narrowly winged. The nutlets are distributed to some extent by either wind or water. The woody root system is spreading and shallow.