Most orchid flowers twist upside down as they open, and for good reason
As a typical orchid bud develops, it rotates a full 180 degrees, a move called resupination. The result puts the showy lip petal beneath the flower's central column, where it can serve insects as a landing platform, or occasionally as a trap. Charles Darwin devoted an entire 1862 book to such tricks.
Orchidaceae ranks as one of the two largest families of flowering plants, with about 28,000 accepted species in roughly 700 genera, somewhere between 6 and 11 percent of all seed plant species. Orchids grow on every continent except Antarctica, though their greatest diversity lies in the tropics, where many live perched on trees. Horticultural societies worldwide have added a huge number of hybrids and cultivars.
The name is blunt. The family is named after the genus Orchis, from the Ancient Greek for testicle, a nod to the paired tubers of some species; Middle English speakers called certain orchids bollockwort. The shorter word orchid was coined in 1845 by the botanist John Lindley. The flowers themselves follow a fixed plan: three sepals, three petals and a three-chambered ovary, with one petal transformed into the lip. Unusually, the male and female parts are fused into a single column, and pollen usually leaves in one packet, a pollinium, capable of fertilising thousands of ovules. It sits on a sticky disc just above an even stickier stigma.
Pollination can be elaborate. Orchids lure insects with colour, pattern, scent and pheromones, and some even imitate female insects. Their seeds are tiny and cannot germinate without help from fungal partners. That fungal dependence goes furthest in coralroot orchids, which have no leaves and draw sugars from fungal threads. Others, such as Taeniophyllum aphyllum, have abandoned leaves and photosynthesise with green roots instead.
Growth takes two forms. Monopodial orchids such as Vanda extend a single stem upward year after year, while sympodial types spread forward from older growth, often forming swollen pseudobulbs. Epiphytes dangle aerial roots sheathed in velamen, a coat of dead cells, and some species, like Catasetum, drop every leaf in the dry season and regrow them.
Source: Orchid
