Hydrolysis of terminal, non-reducing alpha-D-xylose residues with release of alpha-D-xylose. Belongs to the glycosyl hydrolase 31 family. Could be the product of a pseudogene. Inactivating mutations are found throughout the sequence in cv. Wassilewskija (PubMed:20801759) and no expression of the gene is detected in cv. Columbia (PubMed:16267099).