Flower Basics
As we wander in the countryside, or even along the street, it is the flowers of plants that catch our eye first, not the greenery of the leaves and stems, which simply serve as a backdrop to the more colourful petals. Although most species of plants can be identified by details of their various parts, we are drawn to the flowers and it is these that we seek to identify plants by - thus, flowers are the most important starting feature from an identification viewpoint. By chance, the flowers are also the parts by which plants are classified into families and species - this means that the features of a flower tend to be very similar in closely related species, so we can soon get close to an identification simply by - for example - counting the petals and noting the flower colour.
Students of botany will learn the details of flowers at length, even learning a special way of writing down the flower parts in a standard format - the Floral Formula. Such detail is not necessary for the beginner or keen amateur who simply wants to put a name to something, so this account adopts a more simple approach - though it still pays to be careful and accurate with identification.
Flowers follow a regular template, with the parts varying in number and appearance, but always appearing in the same order within the flower. The main parts - working from the outside in - are sepal, petal, stamen, stigma and these are covered in the sections that follow.
Sepals
The sepals form an outer layer around the flower, protecting it in bud and providing support when the flower is open. Sepals are typically green or brownish in colour and there is usually the same number of sepals as petals. Sepals may be rather simple in appearance or they may have toothed or frilly margins; they are usually all equal in size and shape but they may also vary.
One of the commonest changes that may be seen in sepals is that they become fused together to form a tube. However, the original number of individual sepals is usually apparent by the tips of this tube being free and often forming pointed teeth. In species where the sepals are fused, the petals are often fused together, too - and these form the tube-shaped flowers that you see on the colour pages on this site. Sepals fused into a tube often remain to protect the developing seed after the petals drop.
In some cases, the sepals may be coloured to match or contrast with the colour of the petals. In many of the six-petalled flowers, the appearance of six petals is actually due to there being three sepals and three petals of similar colour and shape. In more technical descriptions, sepals and petals that cannot be easily told apart may be called tepals.
Petals
Flowers with prominent and colourful petals have mostly evolved to be insect-pollinated and it's the petals that serve to attract those insects. In flowers that are wind pollinated, the petals may often be missing altogether since they could obstruct the distribution and reception of pollen (grasses, sedges and trees with catkins are typical examples of wind-pollinated flowers).
Petals are highly variable in size, shape, number and colour - all of which helps with identification - and these features can all be checked as part of the identification of a plant. The first obvious way in which petal arrangement can vary is in the flower symmetry. Some flowers have radial symmetry, with the petals arranged evenly in a circular pattern. But other flowers have an irregular symmetry, with the flowers having an obvious 'right way up' and only being evenly symmetrical in a single plane.
Stamen
The stamens are the 'male' part of the flower and each stamen consists of a thread-like filament which is topped with an anther. The anthers are like little sacks that contain the pollen. One little catch is that some species of plants have male and female flowers carried separately. These flowers may be separate on the same plant (e.g. in many trees such as alder, hazel, oak and hornbeam) or may be carried on separate plants (e.g. nettles, hops, some campions), making the plant effectively either male or female. This should always be borne in mind if the stamens or stigmas are proving elusive!
For identification purposes, the anthers can provide important ways of separating some otherwise very similar species. In buglosses, the anthers may or may not extend their tips outside of the cone of fused petals; in mulleins, the anthers may or may not have hairy filaments and in bittercresses, the number of anthers is useful.