Plant of the Week: French Grass (Orbexilum onobrychis or Psoralea onobrychis)

This member of the bean family typically flowers in late May and early June and can reach heights of 2-2 1/2' tall.  It is a much larger and robust species compared to it's cousin, Sampson's snakeroot (Psoralea psoraloides).  The up to 6" long trifoliate leaves have a up to 2" stem that appear off the slightly fuzzy or pubescent stem.  The 2 -6" long raceme of blue flowers (which can vary from light almost white to dark blue) appears at the end of each stem. When each individual flower is examined closely you can tell it has the typical bean family flower. This is a colonial species that spreads vigorously from rhizomes and hence given it's preferred habitat of rich, loamy soil it can form quite a large cluster of plants in a relatively short period of time.  It prefers well-drained soils and grows in the full sun. Most nurseries sell seed of this species and it is not that difficult to grow from seed as long as you scarify the seed prior to planting in a pot or the ground.  It is an uncommon plant in Kentucky and is found at the edge of prairies and in the barrens region. This species has been used for livestock forage in some parts of the world and it is pollinated primarily by bees.  One of the most fascinating things about this plant is that a few years ago a very rare moth caterpillar was found using this species, and only this species, in Ohio.  The adult moth has never been seen and there are no descriptions of the adult moth.  Prior to finding it in Ohio, it was only found in one location in Illinois, Indiana, and Kentucky.