Floral formula
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| ✶ K5 [C(5) A5] G(5) | |
| Floral formula of Anagallis arvensis. Polysymmetric flower. The perianth consists of 5 free sepals and 5 joined petals, which are fused with androecium. Flower is bisexual, it contains 5 stamens, pistil is fused of five carpels, ovary is superior. |
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Narcissus Floral formula |
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Br ✶ ☿ P3+3+Corona A3+3 G(3) Perianth: 6 tepals in 2 whorls of 3 Stamens: 2 whorls of 3 Ovary: Superior - 3 fused carpels |
Floral formula is a means to represent the structure of a flower using numbers, letters and various symbols, presenting substantial information about the flower in a compact form. It can represent particular species, or can be generalized to characterize higher taxa, usually giving ranges of organ numbers. Floral formulae are one of the two ways of describing flower structure developed during the 19th century, the other being floral diagrams. The format of floral formulae differs between authors, yet they tend to convey the same information.
Floral formulae were developed at the beginning of the 19th century. The first authors using them were Cassel (1820) and Martius (1828). Grisebach (1854) used them in his textbook to describe characteristics of floral families, stating numbers of different organs separated by commas and highlighting fusion. Sachs (1873) used them together with floral diagrams, he noted their advantage of being composed of "ordinary typeface". Although Eichler widely used floral diagrams in his Blüthendiagramme, he used floral formualae sparingly, mainly for families with simple flowers. Sattler'sOrganogenesis of Flowers (1973) takes advantage of floral formulae and diagrams to describe the ontogeny of 50 plant species. Newer books containing formulae include Plant Systematics by Judd et al. (2002) and Simpson (2010). Prenner et al. devised an extension of the existing model to broaden the descriptive capability of the formula and argued that formulae should be included in formal taxonomic descriptions. Ronse De Craene (2010) partially utilized their way of writing the formulae in his book Floral Diagrams.
The formula expresses counts of different floral organs, these are usually preceded by letters or abbreviations according to the organ type. They are ordered corresponding to the arrangement of the parts of the flower from the outside to the inside:
The labels with darker backgrounds are less common. "V" used by Prenner et al. for the number of ovules per gynoecium is followed by lowercase letter describing the type of placentation. For epicalyx/calyculus, the letter "k" is used.
The numbers are inserted after the labels, they may be formatted as sub- or superscript. If an organ is absent, its number is written as "0" or it is omitted, if there are "many" (usually more than 10–12) instances, it can be written as "∞". Whorls of the same organ are separated by "+". Organ counts within a whorl can be separated by ":", for example when part of the whorl is morphologically different. A range can be given if the number is variable, e.g. when the formula summarizes a taxon.
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