Xanthocarpia ferrarii (order Teloschistales)
Xanthocyparis nootkatensis (synonymous, order Pinales)
Xanthogramma pedissequum (order Diptera)
Xanthomendoza fulva (order Teloschistales)
Xanthomendoza montana (order Teloschistales)
Xanthoparmelia camtschadalis (order Lecanorales)
Xanthoparmelia conspersa (order Lecanorales)
Xanthoparmelia isiidigera (order Lecanorales)
Xanthoparmelia pulla (order Lecanorales)
Xanthoparmelia salkiboensis (order Lecanorales)
Xanthoparmelia somloensis (order Lecanorales)
Xanthoria elegans (synonymous, order Teloschistales)
Xanthoria fulva (synonymous, order Teloschistales)
Xanthoria montana (synonymous, order Teloschistales)
Xanthoria parietina (order Teloschistales)
Xanthoriicola physciae (order Capnodiales)
Xerocomus guidonis (order Boletales)
Xerocomus subtomentosus (synonymous, order Boletales)
Xerolenta conspurcata (synonymous, order Pulmonata)
Xerophyta dasylirioides (order Pandanales)
Xerosecta explanata (order Pulmonata)
Xerotricha conspurcata (order Pulmonata)
Xerula radicata (synonymous, order Agaricales)
Xiphophorus maculatus (order Cyprinodontiformes)
Xolantha globulariifolia (order Malvales)
Xylaria hypoxylon (order Xylariales)
Xylaria polymorpha (order Xylariales)
Xylocopa flavonigrescens (order Hymenoptera)
Xylocopa violacea (order Hymenoptera)
Xylotrupes gideon (order Coleoptera)
Xymalos monospora (order Laurales)
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