arrhiza

Arrhiza is a botanical term used to describe organisms or plant parts that lack true roots. Derived from the Greek a- (without) and rhiza (root), arrhiza indicates that a plant does not form a conventional root system. In historical botany, arrhiza was often applied to parasitic or mycotrophic plants whose nutrient uptake is accomplished through haustoria or through association with mycorrhizal networks, rather than by typical roots. The term can also describe plant individuals that are entirely rootless, attaching to substrates or hosts by other structures such as rhizomes, stolons, or haustoria rather than true roots. Because it is descriptive rather than taxonomic, arrhiza does not correspond to a specific taxon and is rarely used in modern classifications; contemporary descriptions prefer explicit references to root systems, haustoria, mycotrophy, or symptoms of rootlessness.

In practice, arrhiza may be encountered in older floras or botanical treatises discussing parasitic or non-photosynthetic plants, as well as in horticultural or ethnobotanical literature that notes unusual root morphology. It is related conceptually to terms describing root absence or reduction, such as rootless, haustorial, or mycotrophic plant lifestyles, and to the study of plant–fungus or plant–host interactions.