There may be more than 350,000 species of flowering plants in the world. 70,000 plants are listed by the RHS.
To identify individual species and hybrids we need some form of classification. From the earliest times they have been classified into families and this is largely based on the shape and internal structure of their flowers.
Flowers are the reproductive structures of flowering plants. Since plants cannot move they must rely on wind, water or animals to carry pollen from the male part of one flower to the female part of another flower in a process known as cross-pollination. The flowers of each species are adapted to enable pollinators to carry out this function in the most effective way. This has led to a wide variety of flower forms but constrained within certain family rules. A knowledge of the characteristics of families is useful in flower identification but to identify a species you must first take a close look at the flower and its internals.