I have copied the following from Wikipedia. Trimezia is closely related to the genus Neomarica, and species have been transferred between the two genera. According to Chukr & Giulietti (2001), characters of the flowers do not clearly distinguish the genera, whereas vegetative characters do. Some which they consider diagnostic are shown in the following table. Characters Trimezia Neomarica Underground system always a corm almost always a rhizome, only a corm in 10% of the species Leaf bases (cataphylls) arranged in a spiral arranged in a plane, with the base of one clasping the one above (equitant) Leaves flattened or circular, not folded sword-shaped (ensiform), folded lengthwise (conduplicate) Flowering stem (scape) circular in cross-section (terete), never leaf-like flattened, always leaf-like Equitant is a fun word -- it has nothing to do with equal; rather it's ultimate root is equus (horse), and has to do with the way the leaves stradle one another, the way one stradles a horse. The more immediate root is from the present participle of equitare -- to ride (a horse). I suppose conduplicate and distichous together imply equitant. There is a third genus in the group: Pseudotrimezia. Its flowers are different, with subequal tepals (in the above two genera, the tepals of the inner whorl are geniculate (knee like)). The underground stem is a cormiform rhizome, and the stem is terete.