A dividing wall, for example inside a spur (as in many species of Cleisostoma) or in the trilocular ovary of some Orchidaceae (as in subfamily Apostasioidae, Phragmipedium, and Selenipedium). Plural: septa.
septum in the spur of Cleisotoma sp., after Bauer & Lindley
after Engler and Prantl