The Monandreae have been subdivided into twenty-eight tribes, the characters of which are based on the structure of the anther and pollinia, the nature of the inflorescence, whether terminal or lateral, the vernation of the leaf and the presence or absence of a joint between blade and sheath, and the nature of the stem.
C. Pinch-trap flowers, as in the family Asclepiadaceae, where the proboscis, claw or bristle of the insect is caught in the clip to which the pairs of pollinia are attached.
In orchidaceous plants the pollen-grains are united into masses, or pollinia (fig.
The number of pollinia varies; thus, in Orchis there are usually two, in Cattleya four, and in Laelia eight.
The two pollinia in Orchis Morio contain each about 200 secondary smaller masses.
In Asclepiadaceae the pollinia are usually united in pairs (fig.
- Pollinia, or pollen-masses, with their retinacula (g) or viscid matter attaching them at the base.
The pollinia are also provided with an appendicular staminal covering (fig.