A Grammatical Dictionary of Botanical Latin

trini, trinae, trina (num. adj. distr. pl.): three, three each, by threes, three at a time, three apiece; a set of three, three in a group; threefold, triple = triplex; cf. bini (2), quaterni (4), quini (5), seni (6), septeni (7), octoni (8); used of nouns only used in the plural; see terni,-ae,-a;

        singular                plural
                            m.    f.      n.
Nom.  there is no         trini  trinae  trina
Gen.     singular      trinorum trinarum trinorum
Dat.                            trinis  
Acc.                    trinos  trinas   trina
Abl.                            trinis

- folia quaterna vel sena (raro terna vel quina), leaves 4 or 6 together (rarely 3 or 5) (Stearn).

- sepala petalaque trina, quaterna, vel quina, sepals and petals three, four,or five.

- filis quinis vel forsan trinis, with the filaments in fives or perhaps in threes.

- petala trina ad latus superius posita, petals three positioned on the upper side.

- foliis trinis, with leaves five together.

NOTE: barely distinguished from the cardinal number (three).