An Orchidist's Miscellany

POLLINARIA

 The pollinaria comprises the "package" including the pollen carried by the pollinator during the process of pollination of an orchid. The pollinaria is a composite structure, including:

  • the pollen - in the form of pollinia
  • the viscidium
  • often the caudicles
  • sometimes a stipe


Pollinaria of Fernandezia sanguinea


Pollinaria top view


Pollinaria on top of
toothbick bottom view

Pollinaria showing
movement after
removal

10 minutes later
(Photos approx. 50X
magnification

Photos of pollinea Oncidium cavendishianum

In orchids, the pollen grains are sticky, or grouped together in some way, This aggregation of the pollen grains into pollinia is an adaptation by the plant to the large number of ovules which have to be fertilised. In some general, the pollen remains largely as single grain. In most orchids, however, the pollen forms a more structured mass, held together .by viscin threads. The pollen grains may just be brought together into a fairly uniform .'soft" structure, or may be aggregated into "packets". Some genera have these "packets" covered by a heavy exine coating, to produce the so called "hard" pollinia. The pollinia are mostly moulded into shape by the form of the anther. The number of pollinia per pollinarium varies between different genera, being specific to each genus.

When the pollinia are relatively hard and compact there is usually a softer extension of "tail" by which the pollinia are attached to the viscidium. This viscidium is described sometimes as a gland, comprising a sticky disc of tissue which serves to attach the pollinia to the insect or other pollinator. This is formed from the structure known as the rostellum. It is cellular in origin, some cells of which break down to produce the required "glue".

The "tall" mentioned above involves the caudicles which function both as a "stalk" and as a weak point permitting the pollinia to break away from the viscidium attached to the insect, and stay on the stigmatic surface of the flower being pollinated. Because the caudicles are produced within the anther, they are distinct from the stipe discussed below. The caudicles show structural variation from hard, bony like structures to a clear translucent elastic form which lacks cellular detail.
The next structure sometimes encountered is the stipe. Most Vandoideae and some other orchids have this structure, a strip of non-sticky tissue attaching the pollinia to the viscidium, or, in some cases, a single stipe to which are attached caudicles to individual pollinia where a number are involved. This stipe comprises cellular material derived from the column, and is distinct from the caudicles.

While the structures involved may be small, they are not simple. It is fascinating to see how orchids have developed to ensure the desired and successful natural pollination required for continued survival.


Site established 9th May 1998