This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
With regard to the nomenclature of plants, we have endeavoured to select the names sanctioned by recognised authorities; and in cases where plants are more generally known under erroneous appellations, these are given. In many instances plants possess two or more names. This may have proceeded from different botanists having published descriptions of the same plants unknown to each other, or it may rest upon the views entertained respecting the definition of a genus or species. Oftentimes, however, the advance of knowledge has rendered it necessary or desirable to change the name of a plant. Familiar and important synonyms are quoted to show that they belong to certain plants, and that a plant may, in some instances, bear either of two names with equal propriety, though, generally speaking, the one adopted by the writer who has made that particular class of plants his study is the one to be preferred. It was not thought desirable to encumber the work with the authorities for each name, but where diverse species have received the same name from different authors, the authority is given for the cultivated form or forms. It is the general practice to give garden varieties trivial names, such as those of noted personages, or English or French names denoting some property or peculiarity. And the names of hybrid plants are usually prefixed by a *, to distinguish them from wild forms. For several reasons, the use of Latin and Greek names is more properly restricted to wild forms, but more especially as an indication of the origin of the plant in question.
To those unacquainted with the dead languages, and especially Latin, many of the names given to plants appear almost unpronounceable; and as we give the derivation of most of them, explaining their signification, so we have also marked the syllable on which the accent falls, to indicate their pronunciation. All the letters are pronounced, including the final e, and they are commonly sounded, according to their position, as in ordinaiy English words. But some people affect what is presumed to be the correct pronunciation, according to the Latin language, though there is a wide difference of opinion and usage on this point. With the exception perhaps of the broad sound of the letter a, and the short sound of the letter i, it is safer to pronounce them as English words, subject of course to the difference in accent. There are several ways of marking the accented syllable, but the method adopted in this work is as simple as any yet devised. Some of the names are not correctly accented, because the accents, having to be let in between the lines, are so apt to get displaced. The sign of accent rises from the vowel in the direction of the following consonant, when that is sounded with it; or in the direction of the preceding consonant, when the following consonant does not belong to the accented syllable. Thus, Anemone elegans, Adonis vernalis, and Helleboruts viridis, are pronounced An-e-mo-ne el-e-gans, A-do-nis ver-na-lis, and Hel-leb-o-rus vir-i-dis. Or, to render our meaning more clear, Anemo'ne elegans, Ado'nis verna'lis, and Helleb'orus vir'idis. The few exceptions to the foregoing rule, as, for instance, where two or more vowels come together, seem to require no explanation, as no difficulty is likely to be experienced in ascertaining the correct pronunciation.