Seaside Alder, a tall shrub found along Scarborough Creek below the Arboretum Visitors Center, is native to four counties on the Delmarva Peninsula of Maryland and Delaware, but is also found in south-central Oklahoma and northwestern Georgia. This unusual distribution is not well understood, but temperature and moisture regimes of the regions are somewhat similar. Recent studies suggest that these three distinct populations may be remnants of a former much larger distribution. Seaside Alder may reach heights of up to 20 meters. It has toothed elliptical to ovate leaves that are dark green above and pale green underneath. It is found on damp and wet soils in wetland habitats along streams, rivers and edges of ponds. This alder species has been used in the Philippines in efforts to reforest eroded lands. It has also been used for a variety of folk remedies and for dyes, insect repellants, insecticides, and possible emergency food.

Seaside Alder develops male catkins in the fall (male catkins have been observed in late August on our specimens). The small pistillate catkins develop near leaf bases. In their native habitat these flowers develop in the fall, while our plants develop the flowers in February and March. Seaside Alder has root nodules with symbiotic nitrogen-fixing bacteria, which convert inorganic nitrogen from the atmosphere to a form that can be used by plants.

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