Géneros de hongos: Xanthochrous [36 taxones], Xanthoparmelia [17 taxones], Xanthoria [420 taxones], Xanthoriicola [1 taxon], Xenasma [9 taxones], Xenobotrytis [4 taxones], Xenochora [1 taxon], Xenodiella [1 taxon], Xenodium [1 taxon], Xenodochus [14 taxones], Xenogliocladiopsis [4 taxones], Xenokylindria [1 taxon], Xenolophium [4 taxones], Xenomeris [5 taxones], Xenoplaca [1 taxon], Xenosporium [154 taxones], Xenostele [4 taxones], Xenostigme [1 taxon], Xenostigmella [1 taxon], Xenostomella [5 taxones], Xenotypa [1 taxon], Xerocomus [32 taxones], Xeromphalina [74 taxones], Xerotinus [3 taxones], Xerotrema [5 taxones], Xerotus [39 taxones], Xerula [23 taxones], Xerulina [1 taxon], Xiambola [1 taxon], Xiphomyces [1 taxon], Xylaria [2455 taxones], Xylobolus [68 taxones], Xylobotryum [20 taxones], Xylochora [1 taxon], Xylocladium [2 taxones], Xylocoremium [5 taxones], Xylodon [3 taxones], Xylogramma [3 taxones], Xylographa [23 taxones], Xylohypha [24 taxones], Xylomyces [3 taxones], Xylopezia [4 taxones], Xylophallus [1 taxon], Xylosorium [2 taxones], Xylosphaera [33 taxones], Xylosphaeria [1 taxon], Xylostroma [1 taxon], Xyphium [1 taxon], Xystozukalia [3 taxones]