haustorium

[[File:Hyaloperonospora-parasitica-hyphae-haustoria.jpg|thumb|right|Hyaloperonospora parasitica: hyphae and haustoria]] thumb|right|Haustoria of Muellerina eucalyptoides|creeping mistletoe in a scribbly gum thumb|A coconut sprout, the edible haustorium of germinating [[coconut seeds]] In botany and mycology, a haustorium (plural haustoria) is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates the host's tissue and draws nutrients from it. In mycology, it refers to the appendage or portion of a parasitic fungus (the hyphal tip), which performs a similar function. Microscopic haustoria penetrate the host plant's cell wall and siphon nutrients from the space between the cell wall and plasma membrane but do not penetrate the membrane itself. Larger (usually botanical, not fungal) haustoria do this at the tissue level.

The etymology of the name corresponds to the Latin word haustor meaning the one who draws, drains or drinks, and refers to the action performed by the outgrowth.