plural haustoria 1. botany in (semi)parasitic higher plants, a modified root or shoot serving both to attach the parasite to its host and to obtain nourishment from it 2. in fungi a specialized branch of a fungal hypha that absorbs food for the rest of the fungal colony, often by penetrating the living host cell but not the plasma membrane —note haustorium is the old name for the dwarf mistletoe's endophytic system —see endophyte, holdfast, hyphal hole, powdery mildew, sinker root This definition last updated 10/27/2008