How do cactus survive without water

A. That's the way they're built. Most cacti come from areas of hot weather with low rainfall, so they've had to develop.

Q. Specifically
A. For a start, the spines. They have several uses: they guard against most herbivorous animals; they help shade the plant; and they channel the rainwater to the base of the plant. Then there's the waxy coating ...

Q. What does that do

A. It's called a 'glaucus bloom' and helps reduce evaporation by the plant, trapping in the precious moisture. The cactus also has tighter stomata.

Q. Meaning what

A. All advanced plants have leaf holes called stomata. They open to allow gases and moisture to get in and out of the plant. In cacti, these stomata close tighter than most plants, further reducing the loss of moisture.

Q. Anything else

A. When the rain does fall, cacti can open up pleats - expanding like an accordion - to receive huge amounts of water. Then when the plant is losing water, the pleats fold up, shading the plant more and reducing area exposed to the sun. The plant will also bend over when it lacks water. The amount of water inside the plant affects the hygroscopic pressure that keeps its upright. As the moisture dries out and the pressure reduces, the cactus will droop. As it droops, however, its exposure to the sun is reduced.

Q. What about the roots

A.Cactus roots spread laterally for quite a way in pursuit of water. They are often tiny and may even exist in just a suspended state until the rains activate them, and they grow quickly. After the rain is gone and as the soil dries these feeder roots die back, enabling the plant to live on its store of water without having to spend energy keeping them alive.

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By Steve Cunningham