The Collaborative International Dictionary of English v.0.48:

Arrhizal \Ar*rhi"zal\, Arrhizous \Ar*rhi"zous\, a. [Gr. ? not
   rooted; 'a priv. + ? a root.] (Bot.)
   Destitute of a true root, as a parasitical plant.
   [1913 Webster] Arrhythmic