The Discontinuity Plate, a Definitive Floral Characteristic of the Psoraleae (Leguminosae)

A survey of the floral vasculature of the Psoraleae and other selected papilionoids was made by using cleared flowers supplemented by microtome sections. The tribe is characterized by xylem discontinuities in the ovary traces in the receptacle. At the base of the ovary the three ovary bundles merge and there is a horizontal proliferation of tracheary elements. This plate‐like xylem expansion is not connected to the xylem of the pedicel and is therefore termed the “discontinuity plate.” Xylem in the petal and stamen traces is commonly discontinuous, but the sepal traces are normal. The discontinuity plate and the associated xylem discontinuities are distinguishing characteristics of the Psoraleae. They have not been found in other legumes.