So time and time again I've found that I can't find enough information on dryads, an that I dislike what I do find. So, I've been pondering, and came up with various details for how dryads work. I've come up with enough details to make it worthwhile, so I'm going to compile that information here. So, to begin...
Appearance and Physical Traits:
Most notably in this section is the fact that all dryads are female. There doesn't really seem to be a real reason for this, it's just how it works. Keep in mind that new dryads do not come into being through sexual reproduction, so a second gender is not required.
Dryads always take on some traits from the same kind of tree they are bonded to. There are many ways this can manifest, including leaf-like hair, bark skin, and many others.
Their appearance can be widely varied between different dryads. Thin or curvy, tall or short, any variety of eye, skin or hair colours. Once again, the tree they are bound to has a large impact on this.
Skills and Abilities:
Dryads are, by their very nature, magical creatures, and have very firm roots in nature. They are generally closer to plants than most other fey, but also get along with most animals.
Influencing plants is a major ability they possess. This manipulation is always positive. Helping plants grow, causing them to grow, keeping them healthy, and any other variety of abilities along this line.
Birth, Life, and Death:
A dryad's birth is far different than most other beings, even other fey. The tree that they bond to has to exist first. Only an older, healthy tree will give birth to a dryad. The dryad develops beneath the tree's bark and makes a bulge. After only a few weeks the bark splits and the dryad emerges. A hollow cavity is left behind, and it closes over time.
When the dryad is first born she is as physically developed as a five year old human. This has led to young dryads being called "children of the forest". They are generally not in danger from animals, and if danger threatens they can meld into their tree or use their innate abilities to escape harm.
Dryads develop much faster than other races. by the age of fifteen they have already fully developed. They live long lives, only dying when the tree they are bound to dies or they die through unnatural means.
When a dryad dies and her body decomposes, a tree will grow if possible. It is always of the type of tree she was bound to in life.
A dryad is always bound to a tree. Any type of tree can have a dryad, even treants in rare cases. As previously mentioned, the dryad's appearance and other traits are dependent on the tree she is bound to.
She must always remain within a vaguely defined area of her tree. There are instances of dryads being able to separate from their trees, but this is the exception, not the norm. If she leaves the radius of her bond, first she will feel uneasy. After going further she will feel sick. Further yet will cause her to feel pain until she dies after a number of hours.
A dryad and her tree are very closely connected. If one or the other falls ill, so will the other. If a dryad's tree dies, so will she.
In addition to the tree a dryad was born from, a dryad can live near any tree that grew from a seed that came from her tree. The dryad does not have the same connection to these trees, of course.
As mentioned in the Birth, Life, and Death section, a dryad is born out of an older, healthy tree when certain conditions are met. First of all is the the tree itself. It cannot be a very young tree as it won't be able to support the dryad growing in it. Furthermore, the tree has to flower. The reason detailed in the next paragraph.
A dryad is born when their tree is fertilized by another dryad. This happens through a sort of pollination that the "parent" dryad initiates. This often means that you find dryads in small communities, as their limited range means that a dryad will pollinate nearby trees. Otherwise dryads have no natural means of reproduction. They can engage in sexual intercourse, but cannot be impregnated.
So this is wear I'll throw any information that doesn't fit into the other sections.
Dryads don't normally need to eat. They get all their sustenance from a sort of photosynthesis. It's not exactly like real photosynthesis because she doesn't require any other form of nutrients to live. It is magical in nature. A dryad can eat, though it is generally as a last resort when the dryad is cut off from the sun for too long. It is not a sustainable means of nourishment.
Dryads also don't breath oxygen. Like plants, they inhale carbon dioxide and exhale oxygen. This also contributes to a dryad's blood being clear rather then red.
As I flesh this out and come up with more information, it will be updated.