The floral formula is a form of shorthand that records a flowers structure with a series of symbols, letters and numbers. The information is written down in the order in which the organs appear in the flower, from the outside, inwards. This helps to place a plant in its correct familial relationship.

Floral parts
The abbreviations used:
P (sometimes T used) = Perianth parts
K (sometimes S used) = Sepals
C (sometimes P used) = Petals
A = Androecium (stamens)
G = Gynoecium or Carpels (unit of female part of the flower)

Number of parts
0-10 = Number of parts present in that particular group (or whorl)
oo = Numerous (more than 10) parts
4+2 = 4 in one set, 2 in another
( ) = exceptional, e.g. A4 (5) stamens 4, rarely 5

Freedom or union of parts
( ) = Organs of one kind united or fused
^ = Different organs united

The ovary
Gn (with a stroke below the 'n') = Ovary superior (visible on the outside)
Gn (with a stroke above the ‘n’) = Ovary inferior (hidden indside flower)

Whorls
, = More than one situation present in a whorl
+ = More than one whorl of a particular organ present. (e.g. if there were 4 stamen, 2 were short and 2 were long, that is 2 whorls (or groups), and would be written as 2+2.)

Other abbreviations
Unless otherwise specified, these should be placed at the end of the floral formula.
H = Plant herbaceous
(I’ll have to explain what these other symbols look like)

  • A circle with a cross in the middle or a dot in the middle = Corolla actinomorphic (radial symmetry)
  • An arrow pointing up, or a division symbol turned on its side (a vertical line with a dot on each side) = Corolla zygomorphic (bilateral symmetry)
  • The male symbol- circle with an arrow pointing to the north-east = Male flowers
  • The female symbol- circle with an arrow attached to the bottom = Female flowers
  • The female symbol and the male symbol in one = Flowers bisexual (of both sexes)
  • A vertical line with two circles touching each side, opposite each other (like a plant) = Leaves opposite
  • A vertical line with two circles touching each side, at opposite ends of the line = Leaves alternate.

And here’s the example!
K(5) C(5) A(10) G(2)('n' underlined) (male and female sign inserted here) H

This would mean that the flower had 5 sepals that are fused together, 5 petals which are also joined, 10 stamens, the gynoecium is split into 2 parts (loculus),it is superior, bisexual and the plant is a herb.

Sources
http://www.uq.edu.au/_School_Science_Lessons/UNBiologyTable.html
Plant Identification, by Geoff Burrows (1991)

I only learnt about this today, and I've tried to make it as easy as possible to understand, but if I've done something wrong, please let me know and I can add to this or fix it, thanks!

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