Floral formulas are a useful shorthand and formula for summarizing flower characters that are useful to characterize species and family-level affiliations.
One can expect that the floral formula of a given specimen will be repeated, exactly, or nearly in other specimens in the same family.
Example:
Spiraea
vanhouttei Rosaceae ornamental spiraea
K5
C5 A5x G5
Pyrus
calleryana _ Rosaceae
Bradford pear
K5__C5__A5x G(5)
Cydonia
(Chenomeles) speciosa Rosaceae Japanese
quince
K5__C5__A5x G(5)
All of these species share a 5-merous, radially symmetric flower. The base of the sepals, petals, and stamens are fused into a cuplike structure called a hypanthium. The androecium (stamens) are numerous, usually 4x-5x the number of parts to the calyx or corolla. The only characters that vary are the gynoecium (pistil or pistils) and the position of the ovary (superior or inferior).
Definitions:
K = Calyx
C = Corolla
A = Androecium (stamens)
G = Gynoecium (pistil, pistils)
Numbers correspond to the number of parts in each floral part category
K5 = 5 sepals
__________ = underscore to signify fusion
K5 C5 A5x = fusion into a hypanthium
( ) = fusion of individual parts; eg. K(5) is fused sepals
_____ ___
= superscript to indicate inferior ovary; eg. G(5)
Z = zygomorphic (irregular symmetry); eg. Kz
Sometimes it is useful to add notes concerning placentation, and fruit types.
eg. Axile placentation, fruit an achene, etc.