nPhyllodium(Bot) A petiole dilated into the form of a blade, and usually with vertical edges, as in the Australian acacias.
Century Dictionary and Cyclopedia
nphyllodiumIn botany, a petiole which usurps the form and function of a leaf-blade, as in many species of Acacia. It has usually been further distinguished from a true blade by the statement that it normally presents the edges instead of the faces to the earth and sky; but recent investigation proves that this does not. always hold good, since some undoubted phyllodia are not vertical, but are dorsiventrally placed, like true leaves. The South American Oxalis bupleurifolia is an example. Also phyllode. See also cut under petiole.
Chambers's Twentieth Century Dictionary
nPhyllodiumfi-lō′di-um a petiole which usurps the function of a leaf-blade