|European Black Alder - Alnus glutinosa |
Family Betulaceae - Alder, Birch, Hornbeam
Alders are a key component in waterway soil-stabilization.
European Black Alder, a native of Europe, northern Africa, and western Asia was introduced to North America long ago, and has escaped from cultivation. It is often seen along bodies of water, where it may successfully self-sow and form pure stands. Today, it is grown as a shade tree in urban areas, or at wet sites (ponds, creeks, drainage ditches, etc.) where it thrives and provides both erosion control and ornamental appeal.
European Black Alder is adaptable to a wide range of favorable or harsh environmental conditions. It prefers moist to wet soils of variable pH that are rich and deep, but adapts to average or poor soils that are dry in summer. Growth is especially rapid in occasionally wet to permanently wet areas, such as floodplains , streambanks, and ditches.
Alders have formed a symbiotic relationship with nitrogen-fixing bacteria in the genus Frankia. Nodules formed by Frankia on alders are huge and elaborate, as large as a human fist, with many small lobes. This circumstance puts alders in the happy company of plants (including, most notably, the legumes) able to harness atmospheric nitrogen for their own growth.
Alnus incana subsp. rugosa is an important shoreline and meadow colonizer in boreal and north temperate areas of the Canadian Shield, and a weedy successional species in damp areas along roadsides throughout its range. It overlaps in range and intergrades with A . incana subsp. tenuifolia to the west (in Saskatchewan and Manitoba) and with A . serrulata to the south. It is only slightly differentiated from the more treelike European A . incana subsp. incana . 
Fertilized female flowers become cone-like, green fruits by late spring, and as they grow throughout the summer, they often weigh down the branches that support them. In autumn, the seeds are released as the cones open and the remaining strobiles persist on the twigs.
The birches have long been popular ornamental trees in North America, chiefly in the northern United States and Canada. Several are native Americans, but many species have been introduced from Europe and Asia. Our specimens include river birch, Dahurian birch, Arctic birch, Manchurian birch, Japanese white birch, and 10 other species.
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