The fanstatic orchid diversity has more to do with the fantastic abundance of niches and fantastic absence of limiting factors in the tropics than anything else.
K Barrett N Calif, USA
I believe that the defining characteristic, that is, what separates orchids from other flowering plants, is the union of the male and female sexual organs into a single entity, the column. There are other differences as well, including the ability of a wide range of species and genera to interbreed. I suspect that these differences are inter-related. The column structure is such that fertilization can only be accomplished in nature by a vector such as an insect or a bird. It is very difficult for a an insect to remove the pollinia on the way in. It is relatively easy for an insect to remove it on the way out. Cleistogamy aside, this makes self pollination difficult (except with a toothpick).
I speculate that this makes cross pollination more common in orchids than in most other flowering plants leading to a broadening of the gene pool, rapid evolution and the fantastic diversity we see in orchids today.
Comments, anyone????
Martin Epstein ------------------------------
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