Key to the Subgenera of Notopleura
1. Plants terrestrial, usually unbranched, usually erect; stipules with interpetiolar appendage succulent, or expanded into a membranaceous lamina, or absent; inflorescences pseudoaxillary; pyenes 2, in cross-section hemispherical to strongly dorsiventrally flattened.....Subg. Notopleura
1. Plants epiphytic, usually branched, often clambering or climbing; stipules with interpetiolar appendage succulent or absent; inflorescences terminal or pseudoaxillary; pyrenes 2 to 6, in cross-section hemispherical to triangular or somewhat dorsiventrally flattened....Subg. Viscagoga