Plant species diversity is relatively low, since the flora must be tolerant of salt, complete or partial submersion, and anoxic mud substrate. The most common salt marsh plants are glassworts ("Salicornia" spp.) and the cordgrass ("Spartina" spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat and begin its ecological succession into a salt marsh. Their shoots lift the main flow of the tide above the mud surface while their roots spread into the substrate and stabilize the sticky mud and carry oxygen into it so that other plants can establish themselves as well. Plants such as sea lavenders ("Limonium" spp.), plantains ("Plantago" spp.), and varied sedges and rushes grow once the mud has been vegetated by the pioneer species.