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Alnus serrulata (Ait.) Willd. Hazel alder
Also known as: common alder, tag alder.
Habitat
Hazel alder occurs in scattered, open locations along lake shores and associated somewhat swampy areas, including roadside ditches.
Form
Hazel alder is a spreading to upward-growing, multistemmed shrub, with one or more stems, occasionally having a somewhat tree-like appearance. It grows to heights of up to 5 m. Most stems are up to 5 cm in diameter, but the more tree-like ones may reach up to 12 cm in diameter. Branches tend to arch outward from the stems.
Morphology
The leaves are deciduous, simple, and borne alternately (in a single spiral that distributes leaves in three ranks). Each leaf is 4–8 cm long, obovate to obovate-elliptic (broadest slightly above the middle), broadly wedge shaped to rounded at the base, tapered to an abruptly pointed tip, and finely and mostly evenly small toothed (serrulate) around the margin. Young leaves are slightly sticky; in older leaves, cross veins between the secondary veins are weakly developed and almost ladder like in appearance.
The twigs are greyish brown with surfaces marked by a few paler lenticels. The buds are stalked, obovoid (broadest above the middle and rounded at the tip) with two or three, brown scales of equal length. Each bud is borne above a projecting, roundly triangular leaf scar with three vein scars. The pith of the twig is triangular in cross section.
Both the male and female catkins are preformed and fully visible in unexpanded form over winter. The small female catkins are borne in clusters of two to four, carried on short branches, some of which are angled upwards away from the supporting twig’s direction of growth. The larger (longer) male catkins are borne in clusters of two to five, but these are on branches that are angled abruptly away, and mostly downward, from the supporting shoot’s direction of growth. In the blooming period, the male catkins extend to 3–5 cm, are mottled whitish to yellowish green and brown (with brown anthers), and hang loosely to shed pollen. At this time, their placement below the female ones is distinctive. After the spent male catkins fall from the branches, the female ones go on to form cone-like fruiting structures, 8–14 mm long, made up of broadly tipped, thick, reddish-brown, woody bracts that, when they spread apart in the fall or winter, release small fruits with residual wings, each of which contains a single seed.
The bark of branches and stems is smooth, pale
grey, and marked with similarly colored lenticels that are difficult
to discern.
Notes
The above description is taken from specimens found in southwestern Nova Scotia.
Hazel alder is similar in general appearance to speckled alder (Alnus rugosa (DuRoi) Spreng.), but the details in the description provide several means to distinguish them. The name, speckled alder, comes from the speckled nature of its bark on branches and stems. The whitish, linear lenticels show distinctly against the greenish brown to blackish grey of the bark.
Differences occur in other features. The leaves of speckled alder are ovate to elliptical and thus broadest below or at the middle, and their margins are doubly and somewhat unevenly toothed, and wavy or slightly lobed. The cross veins between the secondary veins are strongly expressed and distinctly ladder like, especially when viewed from the underside. The short stems carrying the clusters of male and female catkins tend not to be angled away from the direction of growth of the supporting twig, so the two kinds of clusters are not widely separated, and particularly, the female ones are not carried upwards and away from the male ones. Also, in bloom, when the male catkins are extended, the speckled alder is less attractive as its male catkins are thicker, mostly dark brown with yellowish overtones, and not as delicately displayed.