Eucalypts vary in size and habit from shrubs to tall trees. Trees usually have a single main stem or trunk but many eucalypts are mallees that are multistemmed from ground level and rarely taller than . There is no clear distinction between a mallee and a shrub but in eucalypts, a shrub is a mature plant less than tall and growing in an extreme environment. "E. vernicosa" in the Tasmanian highlands, "E. yalatensis" on the Nullarbor and "E. surgens" growing on coastal cliffs in Western Australia are examples of eucalypt shrubs.