Phylum Ascomycota Caval.-Sm. (1998) - sac fungi
   Subphylum Pezizomycotina O.E. Erikss. & Winka (1997)
     Class Sordariomycetes O.E. Erikss. & Winka (1997)
       Subclass Xylariomycetidae O.E. Erikss. & Winka (1997)
         Order Xylariales Nannf. (1932)
           Genus Guestia G.J.D.Sm. & K.D.Hyde (2001), incertae sedis