A lot of the time, when I get excited about a topic, I tend to put the apparatus before the Kwalish if you catch my meaning. I've gotten a few messages asking me for some really good examples of how to incorporate plants into a setting and I'm happy to oblige. I'm going to lay out two examples, one is taken from one of my all time favourite settings, and the other is something I created for a custom setting I ran, hopefully they'll help give you some inspiration.
When magic came to the world, it fell from the stars as a seed. A single magnificent seed that burrowed deep into the earth. Over time that seed grew, and grew, and grew. It fed on the natural energy of the world and became rich with magic, the first magic. And after a thousand years that tree bore a single fruit. The person who consumed that fruit was the first spellcaster, and from her descended all other mages. Eventually, this first mage became one with the tree of magic, turning herself into a great living being of magic and wood, but for all her power she was not able to stop her apprentices from sealing her in a great orb of stone that became the moon.
That is a very simplified take on some complex lore, but it establishes several important connections . The idea of all magic coming from a single seed, can show the tremendous power of growth from small beginnings (particularly fitting in rpg's). The idea that magic comes from beyond our world, and that it draws on the power of our planet introduces some fascinating questions about the world of your setting and what lies beyond. The concept of fruit being the medium by which magic became something humans could use can draw exciting religious comparisons. The idea of wood absorbing and suppressing or conducting magic can also have a ton of applications and mechanics. Lastly, the idea of powerful sealing magic forming the moon creates a constant reminder every night about the origin of magic and the moral lessons of the legend (depending on how you spin the story). A simple one paragraph origin for magic helps to create a bushel of blossoming options for players and GM's alike to play off of.
The war between the vampiric blood god and the immortal Lich lord was a fierce and terrible battle. The Vampires were stronger and faster by far, but the lich lord had countless hordes of zombies and skeletons, shambling at his command. But then the Lich lord discovered the Vampires secret weakness to wooden stakes. The cunning necromancer took a battalion of his skeleton warriors and destroyed them, grinding them into necromantic bone meal and using the dust and marrow to feed and nurture those trees. When they grew tall and powerful with shards of bone woven into their bark the Necromancer retook control of the plants, using them as an army of walking undead trees. With countless branches and thorns and minions the Lich the lord was finally able to overcome the so called blood god, impaling him andhis minions and growing great trees around them. To this day the bone wood forest remains, each might tree still feeding off of the necromantic power deep within.
By tying necromancy with trees and life we create a very different dichotomy than we see in most games. The idea of controlling trees and plants with necromancy could spring into an entire academy of "Green" necromancers whose powers are still very much in line with nature. And we have the added bonus of having a spectacularly interesting location. The forest of bone could be a haunting and terrifying place, or a beautiful and majestic monument to the defeat of the blood god, or anything in between. And a setting like that can certainly place a new spin on Treants and other living plant creatures.
Hopefully these examples have been helpful in incorporating plants into your own game.