Blowing hot and cold

Despite being so close to the equator, some African mountains have permanent snowcaps. One of these is Mount Kilimanjaro which is a volcano and is 19,000 feet high. Mount Kenya, also volcanic, is 2000 feet lower but still has its own glaciers. These mountains have unique ecologies adapted to the freezing cold. For instance, giant groundsels and giant lobelias grow at 13,000 feet. Each night the temperature drops so low that they are in danger of freezing solid but during the day the sun beats down so strongly that they risk losing all their moisture through evaporation. One lobelia deals with this in a unique way. The tiny pond of water that accumulates in the leaf rosette freezes over every night, creating a layer of ice that prevents the water beneath from freezing and the frost from reaching the heart of the plant. But the liquid in the rosette is not just rainwater; it also contains pectin secreted from the plant itself and pectin greatly reduces its evaporation during the heat of the day. Another lobelia deals with the changes in temperature in a different way. It grows very tall and has very long leaves, each fringed with tiny hairs that act in much the same way as the fur of an animal, trapping air between them. This insulates the stem from chills and stops the wind from drying it out. Each group of lobelias is the territory of a pair of sunbirds that feed on the insects that are attracted to the plants. The birds keep themselves warm by fluffing their feathers.

Release date: 03 Mar 2011

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