Inflorescences - How they are made



The inflorescences are branches that end with flowers or better with groups of flowers.
The twig of the main axis (rachis) which supports the flower is calledpedicel (which means small peduncle). When there is only one flower at the apex of the stem or at the axil of a leaf, there is no inflorescence and the flower is saidLONELY FLOWER.

The inflorescences are divided into:

  • RACEMOUS INFLORESCENCES or indefinite when the axis has unlimited growth;
  • Selvedge inflorescences or defined are those whose main axis and lateral branches are limited in growth and are characterized by the fact that they all end with a flower;
  • PARTICULAR INFLORESCENCES these are inflorescences which, due to their characteristics, are not similar to the types described above.

These are inflorescences whose axis has unlimited growth. We find the following types:

It consists of an axis on which the flowers are arranged, sessile most of the time, and rarely with a short peduncle. The flowers are always accompanied by bracts.This type of inflorescence is mainly found in Poaceae (former Graminaceae)but not only.

Echium candicans (fam. Boraginaceae)

We have two different types of raceme:
  • simple raceme: it is formed by a central axis on which flowers with peduncles of the same length are inserted in different points along the floral axis. It is therefore very similar to the spike due to the presence of alternate flowers and always accompanied by bracts which, however, in this case are pedunculated (eg lupine, wisteria, orchids, etc.). It is a very common type of inflorescence;
  • compound raceme: in this case the main axis (defined or indefinite) supports groups of racemes. A classic example is grapes.

Simple raceme ofAcanthus spp.

Raceme composed ofAechmea blanchetiana

It consists of a main axis enlarged at the apex from which the peducoli depart which almost all reach the same height. In fact they are often flat, sometimes concave or convex. Also in this case there are concentrated bracts in the point where the peduncles are generated.
  • simple umbrella when each ray of the umbrella of the inflorescence ends with a single flower;
  • compound umbrella formed by rays ending with other umbels.

We find this type of inflorescence especially in the family of Apiaceae (former umbellifers where we find for example theDaucus carota, L'Angelica archangelica etc).

Umbrellas are often equipped at the base of an envelope formed by bracts.

Simple umbrella of the Daucus carota

Raceme composed of the Burnet saxifraga

The branching is the same as the raceme but the peduncles are of such length that the flowers are all at the same level. An example is the pear tree, apple tree, ilsorbo etc.

Corymb of the apple tree

It is similar to the spike but more dense and with a flexible, pendulous axis, generally formed by unisexual flowers.
We therefore find male and female catkins. The flowers have no petals or sepals and the male ones are reduced to the stamens only and the female ones to the stigma. Catkins typically appear in spring, before leaves.
We find this type of inflorescence for example in families Salicaceae (willow, poplar etc.) e Fagaceae (beech etc.).

Willow male catkin (note 1)

Go to:
  • RACEMOUS INFLORESCENCES: ear, raceme, umbel, corymb, catkin
  • CIMOSE INFLORESCENCES: unipara or monocase tip, bipara or dicase tip
  • PARTICULAR INFLORESCENCES: flower head, spadix, cyatium, syconium

1. Image licensed Creative Commons Attribution-Share Alike 3.0 Unported, created by Bogdan Giuşcă

Video: Inflorescence and Flowers

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