Synonyms: why do scientific names keep changing?
Independent taxonomists in different countries may be unaware of each otherís publications, and give different names to obviously identical plants.† Another reason for synonymy applies when, as time goes by, and new names are invented for all variants of a range of plants, it becomes harder to work out to which of these species a new specimen belongs. Maybe it has the fruit shape of species X, the petal shape of species Y.† It may become increasingly obvious that all combinations of fruit and petal shape occur, like height and ear length in dogs. Maybe the flower size, so different in two type specimens, is eventually seen to increase gradually across the continent, with no single obvious place to divide the spectrum. One species name should now be used for all such plants, and the oldest name is then used for all. All the other names become redundant synonyms. In these cases, the species epithet will normally change, the genus part stays the same. For instance, Napoleonaea leonensis became a synonym of Napoleonaea vogelii when it was realised that intermediates existed. The placing of a name in synonymy represents a matter of opinion, and you are not obliged to stop using names once they have been published as synonyms, if you are† well informed and do not agree.
In other cases, two genera may be merged, or a genus may be split into parts, usually because a taxonomist has examined all the described species and decided this describes the variation pattern most realistically. In these cases, the old genus name is retained for some species, and in the case of a split genus, new ones are brought into use for the other species. When a name changes in these circumstances, the genus part will differ between synonyms, yet the species part usually stays the same (maybe with slight changes to the ending to match the gender of the genus name). For instance, Aningeria altissima becomes a synonym of Pouteria altissima when it was decided that African Aningeria species fell within the range of variation of American Pouteria species.