INFLORESCENCE: TYPES, PARTS AND DIFFERENCE WITH FLOWER - BIOLOGY - 2024

An inflorescence is a natural grouping or collection of flowers. These vary widely in terms of their anatomy and arrangement. The characterization of these patterns are usually of taxonomic value. The inflorescences can be compound, at which time they are called sinflorescence.

Most of the inflorescences have a compact appearance, since it is normal that the regions of the internodes do not undergo significant elongation during development.

Aloe hereroensis.

Source: Harald Süpfle

Generally these improve the reproductive success of the plant, if we compare them with a single flower. Together, many flowers increase the visibility of the system towards potential pollinators.

The extensive variability in the inflorescences is due to the immense diversification exhibited by the individual elements that form the floral structures. Examples of inflorescence are magnolias, tulips, wheat, and camellia, among others.

In the event that fertilization of the inflorescence occurs, it will lead to an infrutescence. In this situation, the fruits are united with each other, giving the appearance of a single fruit. Some of them are for human consumption, with high economic value, such as strawberries, figs and pineapple.

Parts of an inflorescence

The botanical terms to refer to each of the parts of an inflorescence are: rachis, rachilla, pedicel and peduncle.

The central axis of the floral structure is called the rachis. If there are lateral axes (they can be secondary, tertiary, etc.) they are called raquilla.

The pedicel consists of the branching that supports each flower, in a compound inflorescence. The axis that supports the entire inflorescence is called the peduncle.

If the inflorescences are grouped together, we speak of a sinflorescence, and the branches that carry the flowers are called paracladia.

There is a type of modified leaf that is born on the rachis of the inflorescence and is called hypsophilic or bract. The appearance of this structure varies widely: it can be colorful, greenish, or have the appearance of an ordinary leaf. The function is primarily protective.

The fruits that derive from the ovaries of an inflorescence are called infrutescence. Like inflorescences, infrutescences are characterized by being a set of small fruits that, generally, retain the structure and shape of the floral structure that originated them.

Types

Botanists have been in charge of establishing multiple categories for the classification of inflorescences, based mainly on anatomical aspects of the flowers. Since 1944, in a review by Rickett (see references), it became clear that the terminology related to inflorescences is confusing.

Inflorescences m onotelas and politelas

Morphologically, a main distinction between inflorescences is the way the axis ends. This classification has two categories or types: monotelas and politelas.

In monothels the axis ends in a flower, where the inflorescence can be closed or defined. Polythelas are the opposite case, where the apical bud is in a vegetative state, and the inflorescence can be open or indefinite.

Racemose and cymose inflorescences

Other authors simply classify them into two types: racemoses and cymoses, when the inflorescence growth is undefined or defined, respectively.

The racemes have the flowers laterally. The inflorescence axis shows an indefinite growth, and the production of flower buds occurs in the lateral regions, which open progressively.

In the case of cymoses, all the flowers are terminal. If we observe the appearance of the cymose inflorescences, they can seem quite similar to the racemoses. However, the differences are based on development pattern and not on mere physical appearance.

Simple and compound inflorescences

Another classification focuses on the product of the axillary bud. In case each of the axillary buds originates a single flower, the inflorescence is simple. If the axillary bud originates another inflorescence, it is classified as compound.

Each of these classifications branches into internal sub-classifications that are beyond the scope of this article. If the reader wants to delve into the different types of inflorescence, he can consult the botanical guide focused on flowers by Plitt, JJ (2006).

Difference with flower

In spermatophyte plants (vascular plants that produce seeds) the flower is responsible for sexual reproduction.

When we think of flowers, we generally conjure up images of colorful and striking structures (whose main function is the attraction of pollinators), which are the typical flowers that we find in angiosperms.

However, floral structures are characterized by their extensive variability within plants. These can be born alone, or in repetitive patterns based on the plant.

In the event that the flowers form natural groups or groups, they are called inflorescences. That is, the inflorescences are a type of grouped distribution of flower structures. They should not be understood as mutually exclusive or contrasting concepts.

In some cases, the difference between the flower and the inflorescence is not so clear. For example, in some individuals belonging to the Potamogetonaceae family, the floral structures appear to be in a transition from a flower to an inflorescence, making identification difficult.

Differences with the stem

The inflorescences have very specific characteristics that allow them to be differentiated from the rest of the vegetative portions of the individual. The most important ones are:

- The stem can grow unlimitedly throughout the life of the plant. In contrast, the growth of the inflorescence is limited, and its life ends once it has fulfilled the associated function: reproduction. In addition, the ramifications of the inflorescences grow in a very short time.

- In the stem the buds are kept in an inactive state, while in the inflorescences the buds generally turn into branches. Thanks to this characteristic, they are usually structures with quite branched appearances.

- The leaves of both structures are different. In the inflorescences we find very heterogeneous leaves, in terms of size, shape and coloration. These modified leaves are called bracts (mentioned above), and they are leaves that help protect the flowers.

References

1. Bentley, R. (1873). A Manual of Botany: Including the Structure, Functions, Classification, Properties, and Uses of Plants. J. & A. Churchill.
2. Bravo, LHE (2001). Plant Morphology Laboratory Manual. Bib. Orton IICA / CATIE.
3. Mauseth, JD, & Mauseth, JD (1988). Plant anatomy. California: Benjamin / Cummings Publishing Company.
4. Peña, JRA (2011). Manual of plant histology. Editorial Paraninfo.
5. Plitt, JJ (2006). The flower and other derived organs. Caldas University.
6. Raven, PH, Evert, RF, & Curtis, H. (1981). Biology of plants.
7. Rickett, HW (1944). The classification of inflorescences. The Botanical Review, 10 (3), 187–231.