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Jai Ganesh

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Registered: 2005-06-28

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Floral Diagram

Floral Diagram

Gist

Floral diagrams are a graphical means to describe the flowe. It is the diagrammatic design of the relative position and number of floral members in each whorl, in relation to the inflorescence or mother axis. The arrangement of floral whorl and other informations regarding the floral whorls, except the position of the ovary can be obtained from the floral diagram.

Details

Floral diagram is a graphic representation of flower structure. It shows the number of floral organs, their arrangement and fusion. Different parts of the flower are represented by their respective symbols. Floral diagrams are useful for flower identification or can help in understanding angiosperm evolution. They were introduced in the late 19th century and are generally attributed to A. W. Eichler.

They are typically used with the floral formula of that flower to study its morphology.

History

In the 19th century, two contrasting methods of describing the flower were introduced: the textual floral formulae and pictorial floral diagrams. Floral diagrams are credited to A. W. Eichler, his extensive work Blüthendiagramme (1875, 1878) remains a valuable source of information on floral morphology. Eichler inspired later generation of scientists, including John Henry Schaffner. Diagrams were included e.g. in Types of Floral Mechanism by Church (1908). They were used in different textbooks, e.g. Organogenesis of Flowers by Sattler (1973), Botanische Bestimmungsübungen[8] by Stützel (2006) or Plant Systematics by Simpson (2010). Floral Diagrams (2010) by Ronse De Craene followed Eichler’s approach using the contemporary APG II system.

Basic characteristics and significance

A floral diagram is a schematic cross-section through a young flower. It may be also defined as “projection of the flower perpendicular to its axis”. It usually shows the number of floral parts, their sizes, relative positions and fusion. Different organs are represented by distinguishable symbols, which may be uniform for one organ type, or may reflect concrete morphology. The diagram may also include symbols that don’t represent physical structures, but carry additional information (e.g. symmetry plane orientation).

There is no agreement on how floral diagrams should be drawn, it depends on the author whether it is just a rough representation, or whether structural details of the flower are included.

Diagrams can describe the ontogeny of flowers, or can show evolutionary relationships. They can be generalized to show the typical floral structure of a taxon.  It is also possible to represent (partial) inflorescences by diagrams.

Substantial amount of information may be included in a good diagram. It can be useful for flower identification or comparison between angiosperm taxa. Paleontologists can take advantage of diagrams for reconstruction of fossil flowers. Floral diagrams are also of didactic value.

Orientation

Diagrams are usually depicted with the subtending bract below and the axis above the flower itself, both in the median line. The axis corresponds to the position of the main stem relative to a lateral flower.  When a terminal flower is depicted, the axis is not present and therefore cannot be shown. Bracteoles, if they are present, are usually drawn on the sides of the diagram.

Symbols used in diagrams

Not only the information contained within diagrams, but also their appearance commonly varies between authors. Just some publications incorporate an overview of used symbols.

Bracts and bracteoles, axes

Bracts and bracteoles are commonly shown as arcs. In Floral Diagrams by Ronse De Craene they consistently have a black fill and a little triangle on the outer side to distinguish them from the perianth. In Eichler’s Blüthendiagramme their representation alters between diagrams.

Floral diagrams and floral formulae

Each of these two concepts is better in expressing some information. Floral diagrams can show the size and relative position of the organs. On the other hand, floral formulae are capable of broader generalization. Prenner et al. view them as complementary methods and state they make an “identikit” flower when utilized together.  Ronse De Craene also approves of their combined use.

Additional Information:

Method of floral Diagram

In order to construction of a floral diagram of a flower, the flower bud is cut transversely and examined with the help of hand lens or so called magnifying glass. The floral leaves are observed in their relevant positions and their aestivation is also clear. The stamens are also observed. Floral diagram of a characteristic bisexual flower’s are two lobed structures. The gynoecium is observed as the centralmost whorl and the chambers of ovary and placentation are noticeably observed.

Description of floral diagram

The following structures the floral diagram may be observed:

a) The mother axis is a black dot outside the furthest whorl of sepal.
b) They are followed by the bracts or bracteoles.
c) The calyx whorl are placed next with free or united sepals, the united nature is represented by in-between lines.
d) The flower portions remaining towards the axis are the anterior part, while the other side is the posterior part of it.
e) The corolla whorl follow the calyx, with free or united petals,
f) The aestivation of corolla along with the arrangement is observed e.g., papilionaceous corolla of pea or two whorled arrangement of Allium.
g) The stamens follow the corolla, which may be few or many, united stamens represented by joining lines (e.g., chinarose), epipetalous stamens represented by lines joining the stamen with corolla e.g., Solarium. The di-dynamic stamen of pea represented by line joined and one free stamen lobe.
h) The ovary is the central-most organ and the placentations are distinctly observed. Sometimes the ovary may be tilted, forming an angle with the mother axis as in family Solanaceae.

Significance of floral diagram

The fallowing matters are indicated by floral diagram:

a) Position of the mother axis can be known.
b) Presence of bracts and bractoles can be undersyand.
c) Number and aestivation of sepals and petals can be counted.
d) Number attachment and arrangement of the stamens may be counted.
e) Number of carpels, placentation and torsion of the ovary also become clear.

What is floral Formulae?

Apart from the graphical diagrams, the flower structure also 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 .....P
Sepals .....K
Petals .....C
Stamens ....A
Carpels ....G

The parts of the flower are described according to their arrangement from the outside to the inside of the said flower. If an organ type is arranged in more whorls, the outmost is denoted first, and the whorls are separated by “+”. If the organ number is large or changeable, is denoted as “∞”.

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