A Floral Prison

This strange-shaped little flower (top photo), about two centimetres tall, belongs to a houseplant known as String-of-Hearts Ceropegia woodii. You can see the whole plant and find more information about how to grow it at http://www.plantoftheweek.org/week098.shtml
This is a plant that takes midges prisoner, to ensure that its flowers are pollinated. When a flower opens it emits a distinctive scent through that lantern-shaped top that attracts tiny midges. Different species of Ceropegia (and there are several) emit different scents that attract different midge species. The midges that are attracted are always females and they force their way in through the hairs in the ‘lantern’ and enter the chimney of the flower, intent on laying eggs. Once inside they encounter hooked, downward pointing cells in the chimney that make retreat difficult so they begin to head downwards, towards a ring of light at the base created by translucent cells at the bottom of the pot-shaped floral chamber. Soon they reach a band of slippery cells with an oily surface that sends then slithering down, through a stockade of downward pointing hairs (see second and third pictures from top) that make escape impossible, into the floral chamber at the base, There are nectaries at the bottom of this chamber, at the base of those minute, vertical, white petal-like structures, and as the midges drink from these they pick up the sticky pollen-producing stamens (small brown object, bottom picture) which become glued to their proboscis. If the midges were already carrying pollen when they arrived they will by now have pollinated the flower, which then lets them go. Once the flower is pollinated the stockade of hairs withers and the flower bends through 90 degrees on its stalk, so the chimney is horizontal and the midges, carrying pollen, can escape. If the midges didn’t bring pollen to pollinate the flower and trigger this release mechanism, they can wait for up to four days for a suitably equipped midge to join them, pollinate the flower and effect release. Once they are out again, carrying pollen, they seek another flower emitting a similar scent and the whole sequence is repeated. And so the flowers are cross pollinated. Ceropegia woodii comes from South Africa and is a very easy, drought-tolerant plant to grow. The one that is the subject of these pictures is growing in a pot on the top of my bookshelves, sending out dangling strings of paired, heart-shaped leaves and weird flowers, as I write this. With the pot high-up and out of sight, I often forget to water it for a week or two, which seems to suit it fine.