Haustorium

A haustorium (plural: haustoria) is a term in botany. It is a root-like structure which attaches to a tree or other plant host. Fungi and parasitic plants like mistletoe use haustoria to get nutrients from hosts.

Haustoria of creeping mistletoe on a Eucalyptus tree

Multiple Mistletoe haustoria on a dead gum tree

Contrast with the term epiphyte, which means "living on". Many other plants live on large trees, but only a few have hausteria.