Magic is an integrated part of most fantasy novels. Yet I have lost count on how many fantasy novels were the heroes travels through a pseudo European landscape and the plants look the same as the plants found on Earth. Which is a big Worldbuilding flaw*, since plants react to the levels of acidity, nutrients and water in the soil. In a fantasy world, there would most likely also be magic residue in the soil. Through the power of genetic selection plants would have adapted tools to survive in the presence of magic.
Based on the adaptions plants have evolved on Earth, it is likely that:
– Some plants would react to magic as a nutrient, and grow faster and larger.
– Other plants would view it as a stress factor, and decrease in size in areas with high levels of magic.
– The levels of Magic residue would also affect the abundance of some plant species. Some would thrive in areas with high levels of magic, while other would dwindle.
– Some plants might reflect the level of magic through different flower colors.
This is just some suggestions on the top of my head, but it is a good starting point. And just this list would affect trade and geopolitics. Take your time, and list some ways you think it can affect your world. And, maybe it will lead to a brand new idea.
*this is based on magic as background factor. I know there are more internal kinds of magic that has a much more limited effect.