Some cacti, like the saguaro, grow to tree size, but true trees need more moisture than most desert environments can supply, so they are scarce on deserts.

• 一些仙人掌，如撒瓜罗，能长到象树那么高。但真正的树却需要比大多数沙漠所能提供的更多的水份，所以树在沙漠里是鲜见的。