Racemose Inflorescence

An inflorescence is the arrangement of a solitary flower or a group of flowers on the specialised floral axis, known as a peduncle or rachis. The inflorescence in which the inflorescence stalk or rachis has indefinite growth (resulting in flowers appearing in acropetal succession) is known as a racemose inflorescence.

Characteristics of Racemose Inflorescence

Growth of rachis is continues and indefinite.
Apex of the rachis might contain a terminal apical bud, but terminal flowers are absent.
Flowers appear in acropetal succession- the lowest flower blooms first, while the uppermost flower blooms last.

Types of Racemose Inflorescence

On the basis of the nature of the rachis, the racemose inflorescence can be of three major types-

Elongated rachis
Shortened rachis
Fleshy and flattened rachis

Racemose Inflorescence with Elongated Rachis

Racemose Inflorescence for Pedicellate Flowers on an Elongated Rachis

Raceme

Rachis elongated, not terminated by any apical flower. Pedicellate flowers appear acropetally from base to apex. Example: Brassica campestris (mustard).

Panicle (Compound Raceme)

Branches (secondary axes) arise from the main axis, and both of them are racemes in nature. Example: Mangifera indica (mango).

Corymb

Pedicels of the flowers show uneven lengths- lowermost flowers have the longest stalks, and uppermost flowers have smaller stalks. Even though the flowers are acropetally arranged, they appear to be situated at the same level. Example: Crataegus (hawthorn).

Compound Corymb

Branches (secondary axes) arise from the main axis, and both of them are arranged in a corymb-like manner. Example: Pyrus.

Raceme Panicle Corymb

Racemose Inflorescence for Sessile Flowers on an Elongated Rachis

Spike

Typical racemose inflorescence with an indefinite rachis not terminated by any apical flowers. Sessile flowers are arranged acropetally from the base to the apex. Example: Amaranthus.

Compound Spike

The inflorescence axis is branched, and the sessile flowers on the secondary axes are more densely borne. Example: Alternanthera.

Catkin (Amentum)

Weak and drooping rachis, with sessile unisexual flowers. The rachis might break from the parent plant, scattering the flowers. Example: Morus alba (mulberry), Salix (willow), Betula (birch)

Spikelet (Locusta)

The basic unit of the inflorescence in Poaceae. It consists of a short axis called the rachilla, bearing one or more florets. At the base, two sterile bracts called glumes are present. Each floret is enclosed by an external larger bract (lemma) and an inner smaller bract (palea). Example: Oryza sativa (rice) and most members of the Poaceae family.

Spadix

Thick, condensed rachis with sessile flowers are covered by one or two large, spathy bracts. Example: Arum.

Compound Spadix

Branched spadix with sessile flowers; each branch represents a spadix with separate, thick, boat-shaped spathy bracts. Example: Banana.

Strobile

A modified spike with persistent, membranous bracts that fall off early, exposing the sessile flowers. Example: Humulus lupulus.

Spike Catkin Spikelet Spadix

Racemose Inflorescence with Shortened or Suppressed Rachis

Umbel

Rachis short and suppressed with a globose head with pedicellate flowers arranged in a radiating fashion. Involucre of bracts are present at the base of the rachis. Example: Centella

Compound Umbel

Branches (secondary axes) arise from the main axis, and both of them are arranged in a umbel-like manner, bearing pedicellate flowers. Example: Coriandrum.

Capitate

Rachis short and suppressed with a globose head with minute and sessile flowers arranged centripetally. Example: Mimosa pudica.

Umbel Compound umbel

Racemose Inflorescence with Flattened and Fleshy Rachis

Capitulum (Anthodium)

The top of the rachis flattened to form a disc-like structure called a receptacle, where the flowers are arranged centripetally, and an involucre of bracts surrounds the base of the rachis. Example: Helianthus annuus (sunflower)- on the receptacle, the sterile flowers grow peripherally as ray florets and the bisexual flowers are present as central disc florets.

Compound Capitulum

The main axis is branched, with each of the branches having a capitulum at its tip; the remaining covered by the same involucre of bracts. Example: Echinops.

Capitulum

Frequently Asked Questions (FAQs)

Q1. What are the different parts of an inflorescence?

A. The parts of the plant associated with the inflorescence are-

Peduncle: The main stalk of the inflorescence; also known as rachis.

Pedicel: The stalk that holds the flower.

Bracts: Modified leaves that can protect or support flowers.

Flowers: The reproductive organs that are arranged in various patterns, resulting in different types of inflorescence.

Q2. What is a raceme with an example?

The simplest type of racemose inflorescence. It has an elongated axis with pedicellate flowers in acropetal order. Example: Mustard (Brassica campestris).