Aecium

1932 August, Ralph Ulysses Cotter, Factors Affecting the Development of the Aecial Stage of Puccinia Graminis, US Dept of Agriculture, Technical Bulletin No. 314, page 29, The writer therefore made observations to determine the conditions under which the aecia open and discharge spores most readily.

The receptive hyphae with binucleate cells eventually form the basal cells of the aecium.[…]Many cup-like structures, called aecia, appear on the lower surface of leaf.

It is a heteroecious rust and its aecia are produced on species of Oxalis, namely O. stricta, according to Arthur (1929).