August 6, 2008

Tree Walk: Unidentified locusts in the Le Conte neighborhood & Trees in the headlines

I was captivated by a pink flowering tree this spring. The flower looks like a sweet pea, but my initially identification took be my surprise because the name is unattractive – the clammy locust (Robinia viscose). I was unfamiliar with the tree, but through observation, particularly of the leaves (pinnately compound, alternate), I figured it was in the legume family. (Like other legumes, the locust fixes nitrogen in the soil.) The City of Berkeley does not publish its tree list online, so I turned to my copy of "Tree, Shrubs and Vines: A Pictorial Guide to the Ornamental Woody Plants of the Northeastern United States Exclusive of Conifers." According to the guide's author, Arthur T. Viertel, associate professor of landscape architecture (!), the leaf stalk and twigs have "sticky glands," hence the name.

However, when I got a chance to feel the stalks and twigs of a tree on Derby, I realized that my identification was incorrect. The stems were not sticky. I have tentatively identified the tree as a black locust (Robinia pseudoacacia) cultivar that bears pink flowers. I write tentatively because the tree is supposed to exhibit thorns, but the cultivar pictured above is thornless. In addition, the tree’s native range is the southeastern U.S. It grows outside its native range, though. Significantly, it is listed as “invasive” in California, according to the National Park Service Alien Plant Working Group. You can read an evaluation of a ‘Globe’ black locust at the Ohio Street Tree Evaluation Project. For more botanical information, visit the tree’s profile at the USDA Plant Conservation Service PLANTS Database. If you are a Bay Area plant expert, please help us verify the identification of this tree.

Trees in the headlines

1 comment:

  1. I think your trees are R. pseudoacacia 'Purple Robe'. I sell a few each spring to customers who see them blooming, the rest of the year they sit there growing bigger without being noticed.

    BTW, I found your blog with a link from pruned.blogspot.com. I look forward to reading more of your posts.

    ReplyDelete

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