100 More Species #45: tar spot; #46: Norway maple

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Tar spot fungus Rhytisma acerinum grows on a Norway maple Acer platanoides leaf.

Forgive me for not presenting a picture of Norway maple in full. Any wide angle photo of my yard is likely to feature them, and you can click the Norway maple link to see dozens of photos of this common naturalized alien. Norway maple is an attractive shade tree well suited to the city and suburbs. It is also a pernicious invasive species, threatening to invade our forests and transform them into barren monocultures. I have cut down all the Norways small enough to yield to hand tools, but several large specimens still dominate the property. The small ones cut down in spring have sprouted fully viable shoots of leaves, and if I didn't continually strip them they would come right back to be giant trees.

Another risk presented by Norway maples is its susceptibility to tar spot, a parasitic fungus that affects only maple trees. It causes no great harm, but can ruin the appearance of foliage (a major part of the New England tourist industry) and potentially weaken vulnerable trees. Norways are so common and so frequently infected, that they must be spreading this fungus to native trees; no alarm has been called, to my knowledge, but we shall see what the next few years brings us.