Robinia sp.

This showy little locust came to Woodlanders by a happy accident. Planted years ago alongside a row of black locusts, Robinia pseudoacacia, on a nearby farm, one tree surprised everyone by opening not the usual white but clusters of vivid rose-purple pea flowers over compound leaves, followed by small, rough, slightly bristly seed pods. The origin is uncertain: a North American species, likely, but possibly a seedling from seed received years ago from China.

The identity remains an open question, part of the plant's charm. The tree may be what is sold as Robinia pseudoacacia 'Purple Robe', or the hybrid Robinia x ambigua, or the plant known in the trade as the Idaho locust, all of them rose-to-purple-flowered locusts of tangled parentage. Whatever the correct name, the result is a fast, showy, small ornamental tree, fifteen to twenty feet, that carries the color with far more flair than the plain white species.

The pendulous clusters of rose-purple flowers open in late spring, fragrant and rich in nectar, drawing bees and other pollinators in numbers. As a legume the tree fixes nitrogen at the roots and improves poor ground, and grows fast into an open, airy canopy. As with all the locusts, though, the bark, leaves, and seeds carry toxic compounds and are not for eating, so site the tree away from grazing animals.

Grow the rose-purple locust as a fast, showy small tree for a sunny, well-drained site, where the spring flower color can carry across a lawn or a border. Adaptable to a range of soils and tough once established, the tree suits a difficult, sunny spot as easily as a garden bed. Give room for the open canopy, pair with other sun-loving plants, and enjoy an uncommon, richly colored locust with a good Woodlanders story behind the plant.