I expect the orthographic correction by the nomenclatural curators of MycoBank and Indexfungorum irritated the authors, but nevertheless the consensus is against 'liquidambar'. They did not explicitly state the use was a noun in apposition in the original publication, and it would be aberrant even if it had been. My colleague Shaun Pennycook comments "The time-honoured standard method for forming an epithet referring to a host is the genitive case, i.e., liquidambaris meaning “of Liquidambar” [see Stearn 4th ed., p. 73, for the genitive ending of a noun ending in --ar] ; and that is how the epithet was presented throughout the 19th and 20th centuries --- I have checked the orthography used by various authors (European, American, Asian) in the >50 liquidambaris names listed in IF, and have not yet discovered any other noun in apposition (only a few spelling errors!). For the sake of consistency, I think the Xylaria epithet correction is justified."