Flower

Operation of the evolutionary forces is more apparent in the androecium than in any other part of the orchid flower. There is a progressive reduction in the number of fertile anthers from Apostasieae to the advanced tribes. In Neuwiedia, a member of the Apostasieae, and considered to be the most primitive of all orchids, the odd anther of the outer whorl and the lateral anthera of the inner whorl are fertile. this is the only orchid in which fertile anthers are present in both the outer and the inner whorls. A slightly more advanced condition is seen in Apostasia and Selenipedium, where the odd stamen of the outer whorl is reduced to a staminode and only the two lateral stamens of the inner whorl are fertile . in the third genus of Apostasieae, Adactylus, even the staminode in the outer whorl is suppressed and only two fertile anthers of the inner whorl are present. In all the monandrous orchids on the other hand, only the odd stamen of the outer whorl is fertile, all the rest being completely suppressed. Thus from the primitive froms like Neuwiedia, where fertile stamens are present in both the whorls, two lines seem to have emerged - those in which the outer whorl is suppressed, eg. Apostasia, Adactylus, Cypripedieae and those in which the inner whorl is suppressed eg. Neottieae, Orchideae and Epidendreae.