Floral diagrams

Floral diagrams are a graphical means to describe the flower. These pictures show a cross-section (or cross-sections) of a young flower or a bud, they can be also defined as a view of the flower perpendicular to its axis. They were introduced in the 19th century and are generally credited to August Wilhelm Eichler, a german botanist.

Two cross-sections (A) and view from the above (B) as a basis for creating the diagram of Oenothera (C).

Parts of the flower are represented by distinguishable symbols. They can be uniform across different diagrams, or can reflect concrete morphology. Rendering of the diagrams usually alters between authors.

Alike diagrams of Vaccinium vitis-idaea. Style above after Rosypal (as in Czech textbooks) and below approximately after Ronse De Craene.

The circle in the upper part of the diagram shows the position of the main stem, this way the correct orientation is ensured. Pointed arcs represent bracts and bracteoles, modified leaves located before the flower itself.

Not all symbols in the diagram have to represent physical structures. Additional symbols include an arrow denoting the orientation of symmetry plane(s), numbers showing the pattern of organ development or a star representing a missing organ.

Floral formulae

Apart from the graphical diagrams, the flower structure can be characterized by textual formulae. Above all, they show the number of different organs, which are preceded by letters according to their type.

tepals	sepals	petals	stamens	carpels
P	K	C	A	G

The parts of the flower are described according to their arrangement from the outside to the inside of the flower. If an organ type is arranged in more whorls, the outermost is denoted first, and the whorls are separated by “+”.

If the organ number is large or fluctuating, is is denoted as “∞”.

Examples of floral formula parts:

• A2+4 – androecium of 6 stamens in two whorls, in the outer there are 2, and in the inner there are 4 stamens
• P∞ – undifferentiated perianth of many tepals

Fusion is denoted by parentheses, if organs of the same type are joined. For fusion between different organs, square […] or curly brackets {…} are used.

• [C(5) A5] – five free stamens fused to corolla, which consists of five fused petals

Ovary position is denoted by over-, underlining or striking the number of carpels in the Czech Republic. In modern English-language publications the letter “G” is altered instead.

• G(5), G(5), G(5) – pistil of five fused carpels, with superior, half-inferior and inferior ovary

Before the organ numbers, sexuality and symmetry of the flower can be written. They are expressed by symbols that often cause problems – they are hard to find, are not included in fonts and seldom render badly.

In Czechia “☿” is usually placed before hermaphrodite flower, pistillate is preceded by “♂” and pistillate by “♀”. Formulae in Floral Diagrams avoid this breakneck labeling, unisexuality is specified by words and hermaphrodite flower have no additional designation.

Floral diagram of Anagallis arvensis after Ronse De Craene. Coloured. Floral formula:

• ☿ ∗ K5 [C(5) A5] G(5) (Czech textbooks)
• ✶ K5 [C(5) A5] G(5) (Ronse De Craene)

It is possible to separate organs with different morphology within whorls, in Czechia by a period, in modern English-language publications by a colon.

Coloured floral diagram of Pisum sativum. The arrow denotes the orientation of monosymetry. 1 – banner, 2 – wing, 3 – keel. Floral formula:

• ☿ ↓ K(5) C5 A(9).1 G1 (Czech textbooks)
• ↓ K(5) C5 A(9):1 G1 (Ronse De Craene)

A dash can be used for denoting ranges (especially when a higher taxon is decribed), e.g. P4–15 – undifferentiated perianth from four to fifteen petals. Commas are used in the sense of “or” in Czechia – A3,6 androecium of three or six stamens.

Spaces are used in different ways between authors. Author of this page means it is the best to write them only between parts of the formula that belong to different organs. This way, the writing is quicker and the formula is easier to comprehend. E.g. ☿ ⤧ K4 C4 A2+4 G(2) is clearer than ☿ ⤧ K 4 C 4 A 2 + 4 G (2).

Comparison

Floral diagrams offer a quicker and clearer compherension of the flower as a whole, while formulae more exactly specify individual information. Formulae cannot describe the spatial arrangement of the flower, on the other hand they are not made unclear by showing concrete organ morphology. Modern authors agree that it is the best to use diagrams and formulae together to combine their advantages.