Placentation

A distinct line of evolution could be traced from the primitive tricarpellary, syncarpous condition with axile placentation to the one-celled ovary with three parietal placentations. The primitive forms are seen in Apostasieae, Selenipedium and Phragmipedium of Cypripedieae and some genera of the monandrous section like Lecanorchis, Eriaxis etc. According to Garay (1960) the reduction from tricarpellary to monocarpellary condition might have come about by a longitudinal splitting of the septa which eliminated the torus, followed by a gradual shortening of the lamellae until only traces are seen on the inner wall. The intermediate forms are seen in Phragmipedium longifolium, where the placentation is between axile and parietal. In Lecanorchis javanica the septa are broken down and torus is done away with. In Limodorum abortivum there is a gradual shortening of the lamellae which is completed in such types as Cephalanthera alba.