What a plant key actually does
A key is a structured set of questions about a plant's features. Each answer rules out some possibilities and keeps others, steadily narrowing a whole flora down to a single species. Traditional printed keys are dichotomous — at each step you choose between two statements (a "couplet"). Modern online keys, like the Key to Tasmanian Dicots, are often multi-access: you can answer the features you can see, in any order, and the key filters the list as you go. Either way the principle is the same — let the plant's characters do the narrowing.
Step by step
- Collect a good specimen. Try to have leaves plus flowers or fruit. Many key steps ask about floral parts, so a plant in flower is much easier to identify.
- Decide the broad group. Is it a dicot, monocot, conifer, fern, moss or liverwort? If you are unsure, see our guide on telling dicots from monocots, or use the key's built-in group identifier.
- Work through the family key. At each step, pick the option that best fits your specimen. Read both choices fully before deciding.
- Narrow to a genus and species. Keep answering; the candidate list shrinks until one name remains.
- Confirm it. Compare your plant against the description, photographs and distribution map provided for that species.
Tips for a reliable identification
- Use a hand lens (10×) for small features such as hairs, glands and the parts inside a flower.
- Examine more than one leaf or flower — plants vary, and a single odd specimen can mislead you.
- If a step is ambiguous, try both branches and compare the final descriptions to see which fits.
- Cross-check the distribution map. A plant well outside its known range is worth a second look.
- Note habit and habitat (tree or herb? wet forest or alpine?) — these often confirm or rule out a candidate.
Plain-language glossary
A few terms turn up again and again in keys. Here is what they mean:
- Simple vs compound leaf
- A simple leaf is a single blade; a compound leaf is divided into separate leaflets.
- Opposite vs alternate
- Whether leaves sit in pairs across from each other on the stem (opposite) or singly, staggered along it (alternate).
- Margin
- The edge of a leaf — it may be smooth (entire), toothed or lobed.
- Perianth
- The sepals and petals of a flower considered together, especially when they look alike.
- Stamen
- The male part of a flower, which produces pollen.
- Ovary
- The part of the flower that contains the developing seeds; it may sit above or below where the petals attach.
- Capsule, follicle, berry
- Common fruit types — a capsule and a follicle are dry and split open to release seeds; a berry is fleshy.
Got a specimen in hand? Put these steps into practice.
Open the Key to Tasmanian Dicots →