Posted on behalf of Alison Abbott
One in seven flowering plants on Earth is an orchid. The Orchidaceae, one of the oldest, as well as the most extensive, families of flowering plants, comprises 749 genera and around 26,000 species. Some have evolved to survive in the most inhospitable of environments, pushing their sweet blooms through the sands of arid deserts or the icy soils of Arctic tundra. All this I learned from The Book of Orchids, a luscious coffee-table tome from Ivy Press (and the University of Chicago Press in the United States), coauthored by Tom Mirenda, Mark Chase and Maarten Christenhusz.
Orchids didn’t achieve their success by being nice guys. They are “Masters of deception and manipulation…famous for lying and cheating,” writes Mirenda, the Smithsonian Institute’s orchid collection specialist, in his introduction.
The book describes 600 representative species, with each photograph reproduced at life size. The selection shows off the aesthetic range of the family, from the startling beauty of Australia’s extravagantly multi-coloured Queen of Sheba (Thelymitra variegata) to the dull arum-leaved spurlip orchid (Pachiplectron arifolium) from New Caledonia, whose puny brown petals make it appear dead.
Introductory essays summarise the unlikely biology of the family and the threats to some of its species.
All orchids begin as a structure called the protocorn, a small ball of cells without roots, stems or leaves. For the embryo to develop, the protocorn needs to be infected by a fungus which provides it with the necessary sugars and minerals.
Nearly all orchid species share two other physical characteristics. Almost without exception, the male and female structures — the stamen and the stigma — are fused into a single column, which makes for unusually efficient pollination. And most orchids have one very distinctive petal that is modified — thanks to an unusual mechanism of genetic control — into a sort of lip upon which pollinators like bees, wasps or moths may land.
The lip is a main site of the orchid family’s deception. Pollinators land in the belief that its patterns promise something attractive, like nectar or a mate. The repertoire of scams in the orchid family is as broad as its range of beautiful form and colour. And the tricks are mean. Flowering plants generally use traits like colour or scent to attract pollinators, and then reward them with nectar so that they return regularly. Most orchids don’t bother with the reward. The pollinators, unsurprisingly, quickly learn not to be fooled.
But that doesn’t bother the orchids. Because of their unusual structure, orchid flowers load vast amounts of pollen onto the back of a naïve insect during its first visit. That load is readily scraped off onto the thousands of ovules in the next flower it visits while it is still working out that it is being cheated. Vast numbers of seeds result from a single encounter.
Orchids can fool by mimicking characteristics of other flowers which do give rewards — some produce look-alike nectar spurs that contain no nectar — or by aping the sexual hormones of insects. Many species have evolved multiple fake lures. The lazy spider orchid (Caladenia multiclavia) from south-western Australia, for example, attracts a local wasp both with sex pheromones and an insect-like silhouette.
Orchids’ sense of entitlement extends to their relationships with fungi, which get nothing in return for their efforts in supplying orchid embryos with vital nutrients. Though some orchids do provide sugars with fungi as they mature, others continue their unrewarding exploitation lifelong.
Meanwhile, humans are doing what they can to challenge orchids’ survival skills. Many species are under threat from collectors supplying them to manufacturers of faddy foods, drinks and therapies. Some of the most beautiful species, like the Queen of Sheba or the Malaysian slipper orchid (Paphiopedilum rothschildianum) are threatened by poachers supplying horticulture.
The Book of Orchids numbers 100,000 cultivars, mostly hybrids, in the horticultural trade. Few reach general retail outlets. For orchid-lovers like myself who select from the offerings of their local garden centre, the book offers (alas) no advice on how best to look after these beauties, but raised my respect for them to a yet higher level.
Alison Abbott is Nature’s senior European correspondent. She tweets at @alison_c_abbott.
For Nature’s full coverage of science in culture, visit www.nature.com/news/booksandarts.