Pollen grains exit single as monads or united in tetrads, polyads, massulae or compact pollinia. United pollen grains have the potential to produce more pollen tubes from a single successful pollination. Do these united grains insure pollination or related to the number of ovules in the ovary to be fertilized?
Pollinia (Orchidaceae) are considered as most evolved type as it transfer as single unit chance of successful pollination would be high. united pollen grains can also common in some of the legumes also.
In case of pollination, it would be depend on pollinator. Every plant have been optimize its pollination system based on ecological condition.
Pollinia in Orchidaceae is a good example, explain that compact pollen more successful in pollination. Almost all pollination in orchid involving insect as a pollinator. But some species have autonomous self-pollination that hypothetically using viscidium disk that attaching below the anther and act as a base of pendulum.
I think, since in united pollen grains (polyads, tetrads, pollinia) factors of quantity and quality are insured, then they are probably more successful in pollination.
My experience working with Ingeae and Phaseoleae(leguminosae) with species that have polyads, indicate that, if the energy inverted in the production of polyads is less, and according with Cruden (1976) the P/O relation show that some species are self-compatible, the study of the reproductive system show that some species are self-incompatible, then one have to study the whole reproductive system in order to analyse all the aspects of a species in order to discriminate if the spacial separation between the stigma and the anthers(hercogamy), or the temporal separation between the stigma recetivity and the anthers dehiscence(dicogamy) or the self-incompability are the factors responsibly of the seed production in plants.
Organizing all pollen grains in a pollinium (Orchidaceae, and also Asclepiadaceae) is a dangerous method. It is like putting all eggs in one basket. Even if the insect pollinator and the pollination method are safe, still lost of a pollinium is a total lost. This is why this pollination method is very rare. However, pollinium has two important advantages. It prevents pollen consuming by the insect; and in case of a very high number of ovules it ensures successful fertilization.
Dear colleagues,
Organizing of pollen grains in pollinium is not dangerous for pollination of orchids !!!
Pollinium is only form of transport and not form of pollination...
Attention !!! The pollination of orchids by insects passed step by step,
the pollinium (all microspores of anther) is only the ‘PDU export’ , but not ‘PDU import’ , witch is a real pollens participate in successful fertilization.
About this reed in my project :
« The way it was in orchids evolution of pollen dispersal units »
and in my Presentation:
Microstructure de pollinies et autre DPU (Dispersal Pollination Units)
Marpha Telepova-Texier
Dear Marpha,
If the pollinium is, as you nicely expressed, the 'PDU export' then lost of this export is a total lost, for all the anther microspores. This looks dangerous. The transport has to succeed! However, since orchids' ovary contains thousands of ovules they have to take this risk. This is the only way to ensure high rate of fertilization. This is why their relation with the pollinator insect is highly sophisticated evolved.
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