A major regional community (*biome
) characterized by low rainfall and consequently supporting little or no vegetation. The term true desert is used of regions completely devoid of higher plant life. Cold deserts include the *tundra
and regions permanently covered with ice and snow. Hot deserts have a mean annual rainfall of under 250 mm while hot semideserts have a mean annual rainfall of under 400 mm. The rain falls in brief heavy showers and vanes in amount from year to year. The plants are few in number and are usually short and sparsely distributed. The permanent perennial plants consist of succulent or xerophytic trees, shrubs, and herbs. There are also *ephemeral
plants whose seeds lie dormant until a brief rainstorm prompts them to germinate, flower, and set seed in a short space of time.