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To understand how botanical names are applied, it is necessary briefly to describe how plants are classified, since the units into which they are separated determine the structure of names.
The basic unit of plant classification is the species (not ‘specie’ – species is both singular and plural in biology) which can be defined as a group of interbreeding individuals producing more-or-less similar offspring and differing from other similar groups by a number of key characters.
Species which share a number of significant features are grouped together to form a genus (plural genera). The characteristics of a genus are often quite easy to recognise, making this perhaps the most generally useful level at which plants can be identified for practical purposes. It is common for a plant to be referred to as, for instance, Malva sp., the sp. being an abbreviation of species and indicating an unidentified species of a particular genus. Genera can vary in size from a single species to over a thousand, depending on their distinctive characteristics. Compare Rhodochiton with Rhododendron for example.
Genera are grouped into larger entities called families, some of which are easily recognised, others less so. Although families may appear at first to be of only academic interest, knowledge of the family to which an unknown plant belongs is the springboard to identifying it, and for the gardener, it can give an indication of the conditions required for successful cultivation.
The majority of families have always had names ending with the same group of letters, -aceae, and based on a genus within the family. This neatly distinguishes family names from genera and other plant groups. However, there are eight families with very well-known names which do not conform to this pattern. While it is perfectly acceptable to continue to use these names, the modern trend is to use alternative names with -aceae endings and this is what has been adopted in the RHS Plant Finder. The families are Compositae (Asteraceae), Cruciferae (Brassicaceae), Gramineae (Poaceae), Guttiferae (Clusiaceae), Labiatae (Lamiaceae), Leguminosae (split into three families based on well-known sub-families: Caesalpiniaceae, Mimosaceae and Papilionaceae), Palmae (Arecaceae) and Umbelliferae (Apiaceae). Also, the traditionally large family Liliaceae is split into a number of smaller, more natural families that may be unfamiliar to readers.
If you find the database useful for your work, please mention it when citing sources of information. It may be cited as…‘The Royal Horticultural Society Horticultural Database’, available at www.rhs.org.uk
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