I am often asked how plants are classified. Here is how it works:
A botanist called Carl Linnaeus devised a scientific way of naming plants in the 18 century. This method is still used today. Botanical names are written in Latin and are understood by horticulturalists throughout the world. Plants with common ancestry are given a name called a family name. A family usually contains a significant number of genera. Plants in the same family often look entirely different so the horticulturalist is often surprised to learn that two entirely distinct plants evolved in this way. For instance, the family Rosaceae contains the genera Prunus and Rosa, yet plants from each of these genera tend to look entirely different. This tells us that the Rosa ‘Crimson Shower’ is in the same family as Prunus lusitanica and this is quite surprising. Rosa ‘Crimson Shower’ has large red flowers and few leaves. In contract Prunus lusitanica has small white flowers and numerous large leaves.
Individual plants are given a first name and this is called the ‘genus’. Plants of the same genus will have a common ancestry, hence they share many characteristics. The genus always is Latin and always begins with a capital letter. An example of a genus is Hebe. Hebes vary considerably in appearance. For example the Hebe armstrongii looks considerably different to the Hebe ‘Autumn Glory’. However, these two Hebes are similar because they are both compact bushes. As we can see plants of the same genus are similar but still entirely distinct.
A plant is given a second name called the species. Plants of the same species share similar characteristics, as they have a common ancestry. Plants of the same species are able to breed amongst themselves. The species name is in Latin and it is descriptive of the plant. The species name may tell us the colour of the plant as in Digitalis purpurea (foxglove). Purpurea is Latin for purple and foxgloves are in the Digitalis genus. In the same way the name of the species may inform us about the plants habitat. For example, Fagus sylvatica (Beach Tree) tells us where the plant likes to grow because sylvatica means ‘forest loving’. Species may also be named after the country of origin as in Mahonia japonica, which is unsurprisingly from Japan. Species can also be named after their growth habit as in Rubus fruticosus (bramble). Fruticosus means bushy in Latin and reflects the growing habit of Rubus fruticosus. In addition species can be named after the discoverer of the plant in question. For example, Darwin discovered Berberis darwinii (barberry) so the species name of this plant is darwinii.
Plants can have many varieties. Varieties can be formed naturally or through selective breeding. Varieties that are formed through selective breeding are called cultivars. An example of a variety that occurs naturally is Fagus sylvatica purpurea.
Cultivars are produced by selective breeding. Cultivars are created by horticulturalists and botanists to ‘improve’ the characteristics of plants. Many ornamental plants are cultivars that are breed to improve the form and colour of their flowers. Philadelphis coronarius 'Aureus’ is a cultivar which has attractive bright, golden leaves that turn soft greenish gold towards the end of the summer. Plants are selectively breed to increase yield, improve flavour, resist disease, increase vigour and so on. The cultivar name is chosen by the breeder, hence this name is in the breeders own language. The cultivar name comes after the species name and it is always in inverted commas. The cultivar name often refers to the name of the breeder. For example there is a plant called Verbena ‘Lawrence Johnston’. This is named after the famous garden designer and plantsman Lawrence Johnston. The cultivar may also refer to the way the plant appears. For instance, Leucospermum ‘Scarlet Ribbon’ appropriately has a red and delicate flower.
Hybrids are formed when two plants of different varieties, species or genera reproduce. This can occur naturally or as a result of selective breeding. They sometimes have highly desirable qualities. Horticulturalists and botanists produce hybrids to ‘improve’ the quality of plants. Hybrids may look more attractive or produce better or more seeds and so on. Hybrid rice has dramatically increased rice yields in China because it grows vigorously. When two plants of different species reproduce they create a hybrid called a interspecific hybrid. Tilia x europeae is an example of an interspecific hybrid. We know this because a ‘x’ is positioned between the names. When plants of different genera cross-pollinate the resultant hybrid is called a bi-generic hybrid. These hybrids have a ‘x’ placed in front of the genus name. An example of a bi-generic hybrid isx Osmaria burkwoodii.