Orchids: Epitome of Plant Evolution

first_img“Orchids might be considered the epitome of plant evolution,” said David Roberts [Royal Botanic Gardens, Kew] and Kingsley Dixon [Kings Park and Botanic Garden, Australia] in a primer on orchids in Current Biology.1  Yet some of the facts they shared about these amazingly diverse and well-adapted plants are puzzling for evolutionary theory.    First, the superlatives.  “The Orchidaceae comprise over 850 genera and 25,000 species, representing about 10% of the world’s flowering plants and the largest family in species number.”  Darwin, who delighted in the study of orchids and wrote a book on them in 1862, estimated that the entire globe could be carpeted with orchids in three generations if all their offspring lived.  Orchids produce multitudes of tiny seeds that can drift long distances.  Their habitats are extremely varied.  Some survive in deserts, many in the tropics, and some without soil (epiphytes).  Some no longer photosynthesize, relying on their hosts for nutrients.  One species even lives its entire life underground.    Orchids maintain remarkable symbioses with pollinators.  Some reward their pollinators with nectar; but, like fisherman, a third of species “deceive” pollinators with lures but no reward.  The article shows a picture of one species that has a structure on its flower that looks like the female of a wasp.  When the male lands on it, a trigger flips him onto his back, dusting the flower’s pistil with the pollen he has collected.  Orchids also have complex dependencies on fungi and on other plants.  The diversity of sizes, shapes, lifestyles and relationships among this group of plants is remarkable.    Since the diversity in this plant group affords many opportunities to study evolution, one might think a great deal is known about it.  Roberts and Dixon mentioned some difficulties, however:Missing branch on the family tree:  “The relationship of the Orchidaceae to other monocotyledons is poorly resolved,” they said.  Monocots are one of the major groups of flowering plants.The plant without a country:  “Equally confused is the geographical origin of the family.”Fossily paucity:  “To date the only unequivocal orchid fossil that has been found is the recently described orchid pollinia on the back of a bee trapped in amber,” said to be 76-84 million years old – but that may be dated assumptions about when bees evolved.The unfit:  “Orchids might be considered the epitome of plant evolution,” they said, “but sadly they are among the most threatened of all flowering plants” – a puzzling predicament for organisms that one would think possess the epitome of fitness.Profusion of confusion:  The authors said that “Numerous hypotheses have been put forward to explain why orchids should have such high levels of deception.”  This suggests that Darwinian theory provides no easy explanation of this phenomenon.In short, “While much still remains to be learnt within orchid biology, there is now a mass of literature on their pollination biology and phylogenetic relationship,” they ended.  This volume of literature does not necessarily track with evolutionary explanatory power: “However, much of this has been the description of patterns; what is now needed are studies into the processes that drive diversification in this most remarkable of flowering plant families.”  Sounds like what is needed is work on the “origin of species,” if you’ll pardon Darwin’s expression (that is, his facial one).1.  David L. Roberts and Kingsley W. Dixon, “Primer: Orchids,” Current Biology, Volume 18, Issue 8, 22 April 2008, pages R325-R329, doi:10.1016/j.cub.2008.02.026.Much of the variation among these remarkably diverse and complex plants fits with horizontal diversification – i.e., segregation of existing information among populations that become more specialized.  Some of the variation is due to loss of function.  The authors did not provide any clear case of new genetic information arising from nowhere.  What Darwin needs to explain is the origin of orchids.  That relationship to other plants, they admitted, is “poorly resolved.”  Equally unresolved is the origin of a new kind of flowering plant.  They are all still orchids.    Here was a natural testbed for evolutionary theory.  Variation within the kind is not the issue.  Some of the theories behind the observed variations (genetic drift, variable reproductive success, arms races leading to exaggeration of characters, founder events) fit within microevolutionary change.  Darwin himself studied orchids with a passion after writing The Origin, and called the origin of flowering plants an “abominable mystery.”  Here we are 146 years later with evolutionists still moaning there is “much still remains to be learnt”.  As far as observational science is concernt, Darwin has been spurnt, and the court is now adjournt.(Visited 31 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img