|INTERNATIONAL CODE OF BOTANICAL NOMENCLATURE online|
18.1. The name of a family is a plural adjective used as a noun; it is formed from the genitive singular of a name of an included genus by replacing the genitive singular inflection (Latin -ae, -i, -us, -is; transliterated Greek -ou, -os, -es, -as, or -ous, and its equivalent -eos) with the termination -aceae (but see Art.18.5). For generic names of non-classical origin, when analogy with classical names is insufficient to determine the genitive singular, -aceae is added to the full word. Likewise, when formation from the genitive singular of a generic name results in a homonym, -aceae may be added to the nominative singular. For generic names with alternative genitives the one implicitly used by the original author must be maintained, except that the genitive of names ending in -opsis is, in accordance with botanical tradition, always -opsidis.
18.2. Names intended as names of families, but published with their rank denoted by one of the terms "order" (ordo) or "natural order" (ordo naturalis) instead of "family", are treated as having been published as names of families (see also Art. 19.2), unless this treatment would result in a taxonomic sequence with a misplaced rank-denoting term.
18.3. A name of a family based on an illegitimate generic name is illegitimate unless conserved.
18.4. When a name of a family has been published with an improper Latin termination, the termination must be changed to conform with the rule, without change of the author citation or date of publication (see Art. 32.7). However, if such a name is published with a non-Latin termination, it is not validly published.
18.5. The following names, of long usage, are treated as validly published: Compositae (Asteraceae; type, Aster L.); Cruciferae (Brassicaceae; type, Brassica L.); Gramineae (Poaceae; type, Poa L.); Guttiferae (Clusiaceae; type, Clusia L.); Labiatae (Lamiaceae; type, Lamium L.); Leguminosae (Fabaceae; type, Faba Mill. [= Vicia L.]); Palmae (Arecaceae; type, Areca L.); Papilionaceae (Fabaceae; type, Faba Mill.); Umbelliferae (Apiaceae; type, Apium L.). When the Papilionaceae are regarded as a family distinct from the remainder of the Leguminosae, the name Papilionaceae is conserved against Leguminosae.
18.6. The use, as alternatives, of the family names indicated in parentheses in Art. 18.5 is authorized.
(c) 2006, by International Association for Plant Taxonomy. This page last updated 12.03.2007 .