Dryad

The Dryad is yet another monster that originated in Greco-Roman mythology. Part of the extensive Nymph family, they are tree and forest spirits; sources conflict as to whether dryad specifically means "oak tree spirit" or just the general term for "tree spirit". They had a vast number of sister species tied to specific trees, including: Daphnaeae (Laurel tree), Epimeliades (Apple tree), Kissiae (Ivy), Meliae (Ash tree), Balanos (Oak), Kraneia (Dogwood), Morea (Mulberry), Igeiros (Poplar), Ptelea (Elm), Aigeiroi (black poplar), Ampeloi (grape vine), Balanis (ilex), Karyai (hazelnut), Kraneiai (cherry tree), Moreai (mulberry), and Sykei (fig).

They are one of the many species of Greco-Roman monstergirls, commonly pursued by their usual boyfriends - satyrs - and frequently lusted after by gods and mortals alike.

In /tg/ media, dryads typical appear as elfin maidens with druid-like powers over plants and, less commonly, animals. They may display some plant-like traits, usually green hair and/or wood-brown skin, and their life is often tied to the health and well-being of a specific tree, due to a confusion between the mythical dryad (spirit of a grove or forest as a whole) and the hamadryad (spirit of a specific tree). Because of these traits, they tend to hate individuals and species who wreck forests for lumber, farmland or just a love of burning shit.

In Dungeons & Dragons

In Dungeons & Dragons, dryads have been around since the beginning, dedicated to protecting their forests, mostly against the likes of orcs and goblins. They get on well with druids and rangers, but aren't very fond of woodcutters. Traditionally, they're described as being beautiful, elf-like maidens and considered to be Good aligned, despite their tendency to abuse their innate Charm Person to turn wandering humans with sufficiently high Charisma into boytoys, a state in which they can be kept as prisoners for years before their captor grows tired of them and sends them away.

In 4th edition, Dryads got shifted out of the "pin-up monster" category by giving them the ability to shift between beautiful elf-maiden form and an armored, female treeman like form, in which state they could be much more aggressively proactive about defending their forests, instead of depending on Charmed servitors.

Hamadryads have less of a presence in D&D, only showing up in 1st, 2nd and 4th edition.

In Warhammer Fantasy

In Warhammer Fantasy, dryads are a key part of the Wood Elf army force. Representing the more powerful spirits of Athel Loren, they bind themselves to living trees to give themselves a way of interacting with the world of flesh. Known for being real bitches who like to lure humans into the forest by assuming the shape of sexy elven women, then assume a monstrous humanoid tree-woman form and rip them apart for kicks.