To understand where the Half Human Half Plants races originates from we have to go way way back to the very start and that is a very small creature. What's special about this Creature is that almost all future races if you trace the path of evolution will all eventually lead back to this one. In truth it has no name but what makes it special is that it posses a special organ or trait whatever you want to call it. It can use it to absorb a special energy within the the atmosphere. While that's all that trait does, how it will expressed in the genes of those that descend from it can be called magical.
So how the Half plant species originates is quite special. It starts when a species of a certain creature arrived on the continent from another on a Wandering Island. A Wandering Island is a island that has under it a special Algae called Gas Trapping Algae and what can be inferred from its name is that it traps gasses or bubbles underwater inside it which is what causes the island to float and move around with the currents. Back to the main topic now the species that arrived on the continent was a very distant ancestor of humans. They actually arrived here under the influence of the Three Rings ai because on the continent there was a Magical disease affecting the creatures causing plants to grow out of them and their skin to slowly turn to wood and often turning into plant that the creature has digested recently or is nearby the Ai deemed it the Plant Mimicking disease.
The Three Rings Ai deemed that it was a highly dangerous evolution and set a plan to eliminate it which is hard without creating cures and the such. When the ancestors of human arrived it wasn't to long before they came into contact with it. Through multiple generations of influence from the disease they eventually built a resistance to the Plant Mimicking disease but it still existed in their bodies growing into some kind of symbiotic relationship this process also affected a couple species of animals. Through this process slowly eliminated the Majority of it there did pop up a variant of it that spread to the ocean but more will be learned about that later.
Through many many years of evolution the plant mimicking disease basically fused with those creatures. This produced many species with plant like traits but only three sentient races who's names are Elf/Elves, Dryads, Ents/Treants.
The Elves can be considered the most special and most numerous of the three as they have the most Subraces of the three as the elve inherited the plant mimicking aspect the best. They look a lot like humans but there especially gorgeous and have long ears but the most special aspect of them is their hair in which plants grow they can also grow them from their body but you'll normally only see it through their hair. They also have a high lifespan up to 300 years. The elves can be split into two Categories which is normal elves and elves that has fused with certain plants and gained plant traits which are called High Elf/Elves. If a high elf had a child they will most likely inherit it, this is how most high elves will be born as the process of fusion is very difficult and can kill the elf and most of the time the fusion is accidental and not done intentionally as the elves of now are not fully aware of how it works. Due to this high elves will group together and form tribes with high elves that have fused with the same plant also elves seem to have no ability to fuse with trees. The elves are split into a few groups normal elves. Underground elves which live underground caverns and whose high elves fused with plants that grow in this caverns and also Crystal Elves who are solely composed of high elves and are a mutation that fused with a special type of crystal also know as a Element. The last type of elves are water elves which are separated into two categories which is the Sea elves and Fresh water elves which are quite self explanatory both possessing high elves that are found in those environments and the sea elves also have a mutation like the Crystal Elves which are the Coral Elves who are all high elves.
The nest Race are the Dryads which can be considered quite special as their an all female race. They can use their hair to connect with plants or trees as their ability is mainly focused with communication with plants. They look human but they can grow bark on their skin by choice and their skin holds a faint green hue. They also sprout a few leaves to. They can have a lifespan of up to 600 years. Their may may of reproduction is by planting seeds into trees in which the Gestation and take up to ten year so amount the three race the Dryads are the lowest in population but they often live in harmony with almost all races even the beastfolk and many predators which is why they aren't outright extinct.
Ents are a very special race as they are a lot like humans from birth but the main thing that sets them apart is that as they get older rather than aging the crib bark until they can't move and become trees and they can become various kinds of trees to. They can live upto 100 year becoming trees. What truely special is that some special Ents can retain their sentience through their process and become what's known as Treants they slowly become bigger and bigger with age and they don't really have a lifespan but it's more about how long they can retain their consciousness which is can be split into a few categories which is 300 years, 600 years, 900 years and beyond and they become more powerful with age.