Iris Cohen schreef
I know the species epithet has to agree with the genus name, and that tree
names are generally feminine. The word arbor itself is feminine. (You'll
never convince me that a ponderosa pine is feminine.)
Now, would somebody please explain Punica granatum and Heptapleurum
arboricola.

***
Well, Punica is feminine and adjectives take the ending -a.
However this applies only to adjectives. If you check Art 23.1 of the ICBN
you will see that a specific epithet can be "[1] an adjective, [2] a noun in
the genitive or [3] a word in apposition". Almost certainly "Granatum" is an
old name for the genus, pre-Linnaean (it was validly published in 1880 for
Punica by Saint-Lager, likely a repeat of pre-Linnaean usage). It is a word
in apposition.
BTW This is one of the reasons some people advocate writing such cases
(an old name of a genus used as an epithet) with an initial capital, in this
case Punica Granatum. The distinction is pretty much lost on the general
public.

Heptapleurum is neuter and adjectives take the ending -um.
If you check Art 23.5 of the ICBN you will see that epithets using "the word
element -cola" may not be used as an adjective (This is wrong in Stearn's
Botanical Latin. This provision only came into the ICBN with the 2000
edition, well after Stearn wrote his Botanical Latin). A compound word
ending in -cola is a noun ("dweller of/in ..."). This noun is a word in
apposition.

PvR
PS You will never convince me a ponderosa pine is masculine. It looks like a
tree rather than feminine, but never masculine.

PS2: See, no police needed. It is an orderly universe after all. Only more
complex than anticipated