When identifying plants, it can be very difficult because many species have marked similarities. However, one of the easiest ways to identify plants is by their leaves.
Leaves come in all sorts of shapes and forms. The aim of plant identification is to find characteristics which link plants firstly through kingdom, subkingdom, order, family, genus, species and finally variety. Each division has fewer characteristics which link the plants in it so you can narrow the plant down to the exact plant you have in front of you. One of the key characteristics by sight are the leaves.
Some plants have sessile leaves, which means they do not have a leaf stalk or petiole. Sessile oak is such a plant and it is this characteristic which distinguishes it from other oaks such as Quercus robur.
Leaf shapes include linear or strap like, palmate, pinnate, bi-pinnate (where leaflets come from the main leaf forming divisions, either paired or alternate). Leaves can also include fronds and adapted shapes like tendrils and these are very useful in helping us identfy plants.
Some leaves are hairy (hursuite) and others thick and waxy which further aids identification. Some have thorns while some are smooth and sheer. Many have wavy margins and others have smooth or entire margins. The leaf venetation can help you to place the plant into monoctyledons or dicotyledons and this really narrows things down when you are identifying.
As well as leaf forms, we can also look at the leaf type itself. Some plants have their leaves adapted into special things suck as spines to protect them from losing too much water through the leaves and also to prevent the main parts of the plant being eaten by animals browsing.
Other leaf types have special tissue in them to aid buoyancy or help with water storage. For example, succulent leaves have water storing tissue while the leaves of many aquatic plants contain air sacs or aerenchyma which helps them to float.
Size of leaf is another important characteristic and helps identification. For example in two Gunnera species, you have one with towering, enormous leaves – G mannicata and one with much smaller leaves (G.brasilica), though they appear to be the same shape. Placing them side by side instantly tells you which leaf came from which species. Similarly with ferms, trees and many other plants, the leaves look the same on different species but are of different size and this is an easy identification route.
It is not so easy then the leaves appear similar like in coniferous trees with their needles and here we look for how they are attached to the tree and petiole. For example one may have needles attached in 3s while another may have paired needles. Once you get the hang of it, identifying plant leaf types and then the plant becomes easier but it takes a lot of practice and you get many wrong initially.