How can we identify a plant?

It is estimated that there are over 350,000 species of plants worldwide [1] so how do we identify one in particular? The first question might be what exactly do we mean by a plant?

As a general rule, plants possess chlorophyll and thus the ability to photosynthesize sugar and other elements from water and carbon dioxide. This complex process enables the plant to be autotroph, that is to produce its own food. In contrast, fungi (and humans) rely on external sources of food for energy and are therefore heterotroph. Cellulose composed of glucose molecules, a primary metabolite of photosynthesis, provides a rigid wall to give plants their structure. Plants are also unable to move so have developed sophisticated methods of protection and reproduction to survive.

Having established that we are looking at a plant, we can look its size. Is it a tree, tree-like (a palm tree, for example), a shrub, a vine or a herbaceous plant? Herbaceous plants have non-woody, flexible stems. Common examples of herbaceous plants are grasses, ferns and daffodils. Herbaceous stems may have small hairs or thorns. Stems can run parrallel to the ground or climb or, in the case of a rhizome, grow underground. Is there just one stem or are there branches coming off from the stem?

Leaves come in a wide variety of shapes, sizes and textures. They may be directly attached to the plant ("sessile") or attached by a stalk (known as a petiole). They can be arranged alternately on the stem, in pairs opposite to one another or in a circle, known as a whorl. The leaf may be simple or compound, meaning that it belongs to a group of leaves. Edges of leaves can vary enormously from undulating to serrated to entire.

Flowers and inflorescences (groups of flowers) are generally the most visible part of the plant. Observing the number and colour of their petals as well as their size and shape can assist in identification. For information on different types of floral symmetry, see the post "What makes a flower attractive?". The type of fruit present may also assist. Finally, the smell of the plant can sometimes provide us with clues to the species.

Identifying plants can be complicated. The reassuring part is that, as with all activities, the more you do it, the better you get! Here are three plants you may already recognise from their leaves. [Check the answer at the bottom of the page!].

If you would like to learn more about identifying plants, see the post "7 details to observe on a leaf".

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[1] Antonelli, A., et al. (2023). State of the World’s Plants and Fungi 2023. Royal Botanic Gardens, Kew.

Three leaves: Sage (Salvia officinalis), Holly (Ilex aquifolium) and Gingko (Gingko biloba)