No such thing as a "male dryad," unless you count satyrs and curetes

In Greek mythology, nymphs are female in both gender/sex and grammar. The word nymph itself translates to "maiden" in English (i.e. a girl of marriageable age). In Greek mythology, nymphs have multiple male counterparts: satyrs, panes, potamoi, tritons, even centaurs (as the mother of all centaurs was a cloud nymph). Of course, that did not stop Paizo from including a male dryad in their Pathfinder comics.

Akoni, male dryad

Nymphs are rustic fey tied to specific environments. According to Mazes & Minotaurs, these environments include woods (dryad), rivers (naiad), seas (nereid), mountains (oread), swamps (limniad), and valleys (napaea).

The concept of a male dryad is nonsensical for the two reasons I mentioned above, as well as a third I mention only now. According to The Oxford Classical Dictionary, the male equivalent of nymphs are the curetes (meaning "youth," i.e. a young man). This refers to a specific group of rustic immortals in the myths, but I see not reason not to expand it to include all the male counterparts of nymphs.