Pollinium, or plural pollinia, is a coherent mass of pollen grains.
They are the product of only one anther, but are transferred, during pollination, as a single unit. This is regularly seen in various plants, such as orchids and some species of the milkweed family Asclepiadaceae.
Orchid genera have mealy pollinia. These are tapering into a caudicle (stalk), attached to the sticky viscidium. They extend into the middle section of the column.
Most orchids have waxy pollinia. These are connected to one or two elongate stipes, which in turn are attached to the viscidium.
The combination of pollinia, caudicles, stipes and viscidium form the pollinarium.
The structural differences in the various flowers ensure that the pollinia are attached to a part of the bee specific to each orchid species: The pollinia of one may be attached to the insect's eye, that of another to the top of the thorax, and that of still another to a foreleg.
The pollinia typically share a single small sticky tab called a viscidium, which adheres to the pollinator when contact is made.
To discourage self-pollination and promote cross-pollination, the pollinia typically are separated from the stigma (female part of the flower that receives the pollen) by a flap of tissue called the rostellum.
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