Floral Formula

Floral formulae and floral diagrams are the two common methods of depicting flower structures. Holding diversity in the positioning of its components, the floral structure is one of the best ways to gain insights into a specific family of plants. The creation of floral formulas began in the 19th century to enhance the floral appearance. It contains numbers, symbols and characters to express the information.

Table of Contents:

Floral Formula
Components of Floral Formula
Symbols in Floral Formula
Writing Floral Formula

Floral Formula

The formula, specific for a family or species, serves the prime purpose of representing the number of floral parts and their relative position concerning the inflorescence or mother axis. The symbols, numbers and characters indicate the number and type of organs, level of ovary, symmetry, presence of fusions and relationship of different floral parts such as calyx, corolla, androecium and gynoecium.

The floral formula also has certain limitations, like the inability to infer details of organ position. The information remains the same. However, the depiction or projection methods differ in America and Europe.

Components of Floral Formula

The floral formula contains five symbols representing:

Number of sepals
Number of petals
Number of carpels
Number of stamens
Floral symmetry

Symbols in Floral Formula

Category	Description	Symbol
Sepals	Calyx or Sepals	K
	Five sepals and aposepalous condition	K₅
	Five sepals and gamosepalous condition	K₍₅₎
Petals	Corolla or petals	C
	Five petals and apopetalous condition	C₅
	Five petals and gamopetalous condition	C₍₅₎
	Five petals containing posterior standard, two lateral wings and two anterior ones forming ‘keel’ while enclosing stamens and pistil	C_1+2+(2)
Whorl	Absence of a particular whorl	0
Whorl	An Indefinite number of floral parts in a whorl.	∞
Tepals	Perianth or tepals	P
Stamens	Androecium or stamens	A
	Sterile stamen or staminode	A⁰
	Epiphyllous steams
	Epipetalous stamens
	Three free stamens	A₃
	4 stamens and 2 whorls	A₂₊₂
	10 stamens as diadelphous, where 9 stamens join to form a single bundle present with one other bundle	A₍₉₎₊₁
Carpel	Gynoecium or carpels	G
Carpel	Steril carpel or pistillode	G₀
Ovary	Inferior ovary
Ovary	Superior ovary
Reproductive structure	Bisexual flower	⚥
	Unisexual and staminate flower	⚦
	Unisexual and pistillate flower	♀️
	Zygomorphic condition	%
	Actinomorphic condition	⊕
Bracts	Bracteate condition	Br
	Ebracteate condition	Ebr
	Bracteolate	Brl
	Ebracteolate	Ebrl
	Epicalyx	Epik

Writing Floral Formula

Here are the steps to be followed to write floral formula:

Step 1: Begin with writing the bract and bracteole.

Step 2: Head on to symmetry and flower sexuality

Step 3: Specify the floral parts such as calyx, corolla, androecium and gynoecium. Write the symbols and numbers with the correct usage of brackets.

Write the numbers with brackets if the flower is fused. If all petals are free, write it simply as a number without a bracket.
Split the values according to the upper and lower lip for the bilabiate structure.
Join the top of symbols of different whorls with a curved line or arc to indicate the adnation of members.
Stretch a vertical line between the symbols of two floral cycles to indicate a break in the alternative nature of floral cycles.
Stretch a horizontal line in front or above the gynoecium to represent the position. It can be inferior, half inferior or superior.

Practice Problems

Q1. Floral bud opening is which type of movement?

a. Paratonic movement of growth
b. Autonomic movement of growth
c. Autonomic movement of locomotion
d. Autonomic movement of variation

Ans. b. Autonomic movement of growth

The movement of structure here is determined by responsive organs rather than stimulus.

Q2. Which flower has a keel?

a. Bean
b. Gulmoher
c. Cassia
d. Calotropis

Ans. a. Bean

Keel is the presence of two-in-one petals, as seen in bean flowers.

Q3. The arrangement of floral or leaf structure so that margins of each structure touch each other without overlapping?

a. Twisted
b. Imbricate
c. Valvate
d. Marginal

Ans. c. Valvate

Twisted aestivation exhibits overlapping, while imbricate aestivation exhibits exterior and interior placement of the structure.

Frequently Asked Questions

Q1. What is a zygomorphic flower?
Answer: A flower that divides into two equal halves replicating each other on cutting through the longitudinal plane is zygomorphic.

Q2. What is the example of an actinomorphic and zygomorphic flower?
Answer: The Gulmohar and sunflower are zygomorphic flowers, while the hibiscus is an actinomorphic flower.

Q3. What are the different types of placenta in flowering plants?
Answer: There are five types of placenta arrangement, marginal, basal, axile, superficial and parietal.