RHIZOBALUS, in botany: A genus of the traginia order, belonging to the polyandria class of plants; and in the natural method ranking under the 23d order, Tribulate. The calyx monophyllous, fleshy, and downy; the corolla consists of five petals, which are round, concave, fleshy, and much larger than the calyx; the stamens are very numerous, filiform, and longer than the corolla; the styli are four, filiform, and of the length of the stamens; the pericarpium has four drupæ, kidney-shaped, compressed with a fleshy substance inside, and in the middle a flat large nut containing a kidney-shaped kernel. Of this there is only one species, viz. Pekia. The nut is sold in the shops as American nuts; they are flat, tuberculated, and kidney-shaped, containing a kernel of the same shape, which is sweet and agreeable. Clusius gives a good figure of the nut, and Aublet has one of the whole plant.