The higher-level classification of Orchidaceae has traditionally
been based on the construction of the fused gynoecium and androecium
(gymnostemium or column), which is, in its details, unique to
the family. The number of anthers has been the primary trait
emphasised, which has resulted in the family being split into three
groups, often recognised as subfamilies. Those with two anthers or
one anther were placed in Diandrae and Monandrae, respectively.
Two south-eastAsian genera, Apostasia and Neuwiedia (Fig. 1), were sometimes
viewed as orchid relatives, but were considered by many
authors to be a separate family, Apostasiaceae, more closely related
to other families such as Hypoxidaceae (Hutchinson, 1959) than to
Orchidaceae. We have demonstrated with DNA studies that these
two genera are exclusively related to the rest of the orchids, and it
has been shown that they also have a typical orchid protocorm
(Kristiansen et al., 2001), so there is now a third type of orchid