ORCHIDS
Orchids belong to the angiosperm group of flowering plants and count a close evolutionary kinship with the ancient asparagus family. The angiosperm group arose 120 to 130 million years ago during the early Cretaceous Period and it has been one of the most significant events in the history of the Earth. To this day researches are still challenged by the mystery of the origin of the angiosperms from the non-flowering gymnosperms, their rapid diversification and rise to dominance.
Orchids are the largest and most diverse plant family on the earth comprising 8% of all flowering species and to date number at 22,000 individual species with the number still increasing as more are discovered. Most frequently we are aware of the tropical orchids and their magnificent blooms, however there are many more small flowering varieties which easily escape our notice. A number of the later are found in Australia scattered in the eucalypt forest, woodlands and mallee where they are tucked away in the under story and generally pass unobserved.
Recent research has found that two factors have enabled the orchids to evolve into the vast number of different species. These are pollination and fungi.
Firstly it is the highly adaptable way individual species interact with the pollinators, especially the bees. It has been discovered that two species of adjacent living orchids were found, due to their individual morphology, to dab only a specific but different location on the bee with their pollen. The bee is the unwitting carrier of pollen from both orchids and the specific location ensures that pollen from one species can only be passed to an orchid of the same species. Specific customer service!
The second is the relationship of individual species of orchid to specific species of soil fungi. This is a symbiotic relationship with both parties benefiting, the orchid receiving essential minerals and trace elements from the fungi which in return receives sugars from the orchid. With this strategy different species of orchid can live side by side without direct competition.
Research on a number of tropical orchids from South-East Asia in contrast, found that they rely on a wide range of fungi and these provide the orchid with carbon. This relationship is vital for the orchids as they have no chlorophyll and cannot generate their own. A carbon isotope study revealed that the fungi were in fact acquiring the carbon from the roots of adjacent trees, with which they also have a relationship, and passing it on to the orchids.
An Australian parallel is the research work carried out by Associate Professor Mark Brundrett from the University of Western Australia, and published earlier this year. The subject of the study was the critically endangered orchid Rhizanthella gardneri which is fully subterranean and has no green parts. Although it still retains some chloroplasts 70% of the genes in the chloroplast have been lost. This orchid also has a symbiotic relationship with a specific fungi which in turn has a relationship with the roots of a broom bush from which nutrients are acquired and passed on to the orchid. There are only 50 known individuals left in the wild.