In naming cultivated plants, a Group (formerly cultivar-group) is a formal classification category, under the International Code of Nomenclature for Cultivated Plants (ICNCP):
- ICNCP Art. 3.1: "a formal category for assembling cultivars, individual plants or assemblages of plants on the basis of defined similarity."
Every word in a Group epithet (name) is capitalised, except where not permitted by English-language custom, e.g. conjunctions, prepositions (that do not begin the epithet), and words following a hyphen (that are not proper names). (Art. 21.3)
The term "Group" (with a capital G) was introduced in the 2004 ICNCP, replacing the "cultivar-group" of the 1995 ICNCP.
A Group is united by some common trait; for example there may be a Group of yellow-flowering cultivars, a Group of cultivars with variegated leaves, a Group of cultivars resistant to a particular disease, etc. A cultivar may belong to more than one Group (for example, it may be yellow-flowering, with variegated leaves and resistant to the disease at one and the same time, or another time).
- ICNCP Art 9, Ex 10: "Solanum tuberosum 'Desiree' may be designated part of a Maincrop Group and a Redskin Group since both such designations may be practical to buyers of potatoes ..." [capitalization in original, as required by the ICNCP]
Another reason for designating a Group is when a well-known plant loses its taxonomic status (e.g. it ceases to be a "good" species or subspecies and becomes a synonym). Its botanical epithet may be retained in a "Group epithet". For example, Tetradium hupehense is sometimes regarded as being part of Tetradium daniellii, and the plants in question may then be referred to as Tetradium daniellii Hupehense Group.
- Brickell, C.D. et al. (eds) (2009). "International Code of Nomenclature for Cultivated Plants" (PDF). Scripta Horticulturae (8th ed.) (International Society of Horticultural Science) 10: 1–184. ISBN 978-0-643-09440-6.