This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
In botanical names derived from Greek or Latin words, their compounds, or derivatives, the accent, according to the ordinary rule, is placed upon the penultimate syllable, if it is long in Latin quantity; otherwise, upon the antepenult. Many names, however, have been given to plants in honor of individuals, which, having nothing Latin about them except the terminal form, and the pronunciation given to them by botanical authors being diverse, are here accented like the names of the persons, so far as euphony will permit. This rule is followed because it is believed to agree with the prevailing usage among botanists in ordinary speech; because it is in accord with the commemorative object of such names, which ought not to be obscured by a forced and unnatural pronunciation; and because the test applied to words properly Latin, viz., the usage of the Latin poets, cannot be applied to words of this class. We therefore give Torreyi, Vaseyi, Careyi, Jamesii, Alleni, rather than Torreyi, Vaseyi, Careyi, Jamesii, Alleni.
The acute accent is used to denote the short English sound only; as in bat, bet, bid, not, nut; the grave accent, to denote either of the other English sounds, whether long, broad or open; as a in bale, ball, bar, bare, laud; e in eve, there; i in pine, pique, machine; 0 in note, move; u in pure, rude. The accent for the short or longer English sound is based upon current English usage, as given in the chief English dictionaries from Walker's to the most recent, and without reference to the supposed ancient pronunciation.
Much diversity has been found in botanical works in the accented syllable of many modern Latin adjectives ending in -inus, -ina, -inum, derived from Latin words. As these adjectives are derived from Latin roots and are regularly formed, their pronunciation should properly follow classical analogies. When signifying, or referring to, time, material, or inanimate substances, they should, therefore, according to Andrews & Stoddard's rule, have the penult usually short, and the accent on the antepenult; as in gossipina, cannabina, secalina, salicina, amygdalina, and other adjectives derived from plant names, like the classic nard-inus, cyprinus, faginus. When these adjectives have other significations than those above referred to, the penult under the ordinary Latin rule is usually long and accented; as in lupulina. leporina, hystricina, like the classic ursina, canina.