Robinia x ‘Purple Robe’ – Locust – 20-Gallon


In most horticultural circles, this medium-sized tree with bright purple flowers is thought to be a cultivar of Black Locust, Robinia pseudoacacia. However that tree doesn’t seem to ever have flowers with a color other than white. There are a couple of relatives in this genus, Bristly Locust (R. hispida) and Clammy Locust (R. viscosa) which do have pink to purple flowers.  Turns out, these species are indeed the source of the purple color of ‘Purple Robe’ flowers. First, Black Locust was crossed with Clammy Locust to create a hybrid R. ×ambigua ‘Decaisneana’. That hybrid was crossed with R. hispida ‘Monument’ by William Silva of Sebastopol, California in 1964 to create ‘Purple Robe’. Like Black Locust, flowers are fragrant and attractive to pollinators.

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Photo by David J. Stang, CC BY-SA 4.0, via Wikimedia Commons

Updated 8 October 2021