This name is a synonym of Psidium guajava L..
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 454404) with original publication details: Revis. Gen. Pl. 3(2): 91 1898.
This name record (from WCSP) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Myrtus guajava in version 1 of The Plant List.