In Norse mythology, Yggdrasil (Old Norse Yggdrasill, ; the extra -l is a nominative case marker) is the "World Tree", a gigantic ash tree, thought to connect all the nine worlds of Norse cosmology. Sometimes it is called MÃmameiðr or Lérað. According mythology, Ãsgard, Ãlfheim and Vanaheim rest on the branches of Yggdrasil.