Ontogenesis of monad pollen inPterostylis plumosa (Orchidaceae,Neottioideae)

Pterostylis plumosa (Neottioideae) is an orchid with monosulcate monad pollen. Tetrads may be isobilateral, decussate, tetrahedral, rhomboid or T-shaped, but all pollen grains have a similar shape. Those belonging to the same tetrads are contiguous from microspore release to opening of the anther, with the furrow oriented inwards. Sporophytic proteins are present outside the furrow. The tapetum is of the parietal type without orbicles. The increase in pollen grain size between meiosis and maturity is only three-fold. The generative cell is spherical when the pollen is mature. These features are discussed in relation to the primitive nature of the species.