1. Hardy deciduous vine having large leaves and flowers with the calyx tube curved like the bowl of a pipe
   - Dutchman's-pipe, pipe vine, Aristolochia durior

Type of: Aristolochia clematitis, birthwort

• genus Xanthomonas
• genus Xanthorroea
• genus Xanthosoma
• genus Xenicus
• genus Xenopus
• genus Xenorhyncus
• genus Xenosaurus
• genus Xeranthemum
• genus Xerobates
• genus Xerophyllum
• genus Xiphias
• genus Xylaria
• genus Xylocopa
• genus Xylomelum
• genus Xylopia
• genus Xylosma
• genus Xyphophorus
• genus Xyris
• genus Yucca
• genus Zaglossus
• genus Zalophus
• genus Zamia
• genus Zannichellia
• genus Zantedeschia
• genus Zanthoxylum