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Alders erupt at the Arnold Arboretum

by William (Ned) Friedman, Director of the Arnold Arboretum
May 3, 2017

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Alders erupt at the Arnold Arboretum

With so much in flower right now at the Arboretum, it is hard to know where to begin or what to focus upon. Indeed, each walk is a chaotic overload of nature’s springtime ephemera. Maples (Acer) with their subtle but magnificent small flowers, chains of yellow flowers on the winter-hazels (Corylopsis), shadbush (Amelanchier), dogwoods (Cornus), flowering quince (Chaenomeles), ash (Fraxinus – can you conjure an image of ash flowers?), hornbeams (Carpinus) and birches (Betula) loaded with pollen-bearing catkins, clouds of yellow forsythia (Forsythia), and last week, the peak of the flowering cherries (Prunus).


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That said, one of my favorite moments came while strolling Willow Path, in the alder (Alnus) collection. For years, I have been trying to get a few good pictures of alder flowers and bud break – to no avail until this past week. Two montane alders (Alnus maximowiczii; 1462-77*E), a species native to Japan (where they were collected), Korea and far eastern Russia, were in perfect bloom, with profuse catkins of pollen-bearing flowers (left image) dangling in the breeze. The seed-producing flowers are borne on separate inflorescences (upper right) and the bright red stigmas (the part of each flower that receives pollen) make a dramatic show against the blue sky. Lower right, a bud erupting with this year’s foliage leaves.

An interesting side note on alders: Alders harbor symbiotic “nitrogen-fixing” bacteria in their roots. These bacteria, in the genus Frankia, take nitrogen gas (N2) right out of the air and convert it to ammonia (NH3), a nitrogen-bearing molecule that can be used by plants as a nutrient. In this symbiotic deal, the bacteria get a home and photosynthetically-produced sugars from the alder, and the alder gets nitrogen fertilizer.

One thought on “Alders erupt at the Arnold Arboretum

  1. Dear Dr. Friedman, I just saw the Austrobaileya scandens opening on the Arnold Arboretum website. I just read your blog. You are so educated. You explain things so well. Sincerely, Cheryl A. Joseph, Boston College, B.S. Biology, class of 1974, M.Ed. 1980, past Arnold Arboretum Children’s Tour Guide

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