Beyond our purpose in inventing a plant or animal, we can think about how they are used by our world’s inhabitants. Food is an obvious way, and some food will have cultural or religious ideas associated with them; some items might be forbidden or ritually slaughtered first, though we’ll want a rationale for such decisions, such as deciding an animal offended a god. Imagine a deity who was once on an important mission that became delayed by a herd of animals, or by a forest of a given tree type; now this is seen as the reason the god failed to achieve something. The resulting religion could forbid use of the item, either by the god’s decree or not.
Plants are used in many ways that we can adopt when inventing one. The obvious example, besides creating oxygen, is for food, but there’s also decoration, medicine, building materials, toys, clothing, tools, fuel, and everyday items like pencils and paper. Chemical processes often require or benefit from plants, such as fermenting beer or brewing coffee. Many of these aren’t glamorous or of much interest to an audience, but when doing research on analogues, you’ll learn what any given plant is typically used for and can leverage the information.
Often, not every part of a plant has the properties that make it special. The leaves can be deadly while the stem or seeds are not. When crafting a plant, decide which part makes it valuable and if anything must be done to that part for it to acquire its purpose. Leaves might need to be crushed. The pulp might need to be boiled.
Decoration is a useful subject if we decide that people in a given culture have assigned certain properties to a flower, for example, and assume that a female wearing one in her hair is revealing something about herself to others. Garlands of a given flower type can be used at ceremonies, such as burial or graduation. These uses require less invention of details because an audience will accept them as cultural and having little basis.
Plants offer a good opportunity to have our characters and story affected by interesting foods. They can be poisonous, addictive, a bland staple for adventurers, freely found in the wild, or a cultural or religious expectation to serve or consume at certain moments. A culture clash can result for traveling characters. Even if we don’t use plants in a significant way, they can still be briefly mentioned during any scene involving their consumption.
Invented medicinal plants are great for healing or poisoning our characters or for use in spells. We need no explanation for why a plant has these properties because audiences don’t expect one, though in a more scientific world or story, one will help. Plants with supernatural properties are often said to grow near something like a special spring or dark place. The habitat can be the reason the plant acquires unique properties—or even loses them if away for too long, such as once plucked. Are the plants themselves supernatural?