Racemose and Cymose Inflorescence | Botany

In this article we will discuss about Racemose and Cymose Inflorescence.

I. Racemose Inflorescences:

i. Raceme:

It is a racemose inflorescence in which the main axis goes on producing lateral stalked or pedicellate flowers in acropetal order. Example—Crotolaria (B. Atasi, Fig. 77, A), mustard. A compound raceme, in which the rachis is branched and branches bear the pedicellate flowers in racemose fashion is called panicle, e.g. Peltophorum.

ii. Spike:

It is just like a jaceme, but the flowers are sessile, e.g. Achyranthes (B. Apang), tube-rose (Fig. 77, B).

iii. Spadix:

It is a kind of spike having a fleshy axis with sessile flowers, which remains enclosed in the coloured boat-shaped bract, the spathe. Familiar examples are arum (Fig. 78), banana. Palms have branched spadix.

iv. Catkin:

It is a spike with long pendulous axis bearing only unisexual flowers, e.g. Mulberry (B. Toonth).

v. Corymb:

It is a racemose inflorescence in which the main axis is comparatively short -and the older flowers have longer stalks than the younger ones, so that all of them are raised more or less to the same level. Example—Iberis (Candytuft, Fig. 79, A).

vi. Umbel:

Here the main axis is very short and a number of flowers with pedicels of same length develop from a point giving the inflorescence an umbrella-like appea­rance, e.g. Hydrocotyle (B. Thulkuri). Bracts often develop at the base of the pedicels. Coriander (B. Dhoney, Fig. 79, B). Anise (B. Mouri) are good examples of compounds umbels.

vii. Capitulum:

In this case the rachis is very much shortened to form a flat convex body called receptacle. Many sessile flowers are present on the receptacle in centripetal order.

The florets are usually of two types, ray florets at the circumference and the disc florets at the centre; the florets have small scaly bracts and the whole inflorescence is surrounded by an involucre of bracts. Though it looks like a single flower, it is really an inflorescence. Familiar examples—sunflower (Figs. 80), marigold, Dahlia, and other members of sunflower family.

II. Cymose Inflorescence:

In cymose inflorescence the-main axis is terminated by deve­lopment of a flower. Lateral axes, one or more bearing younger flowers, originate from below the terminal one. The arrangement is basipetal, i.e. oldest one at the tip and the younger ones away from it. Thus the mode of opening of flowers here is centrifugal (from centre towards circumference).

According to the branches formed, cymose inflorescence may be:

(i) Uniparous,

(ii) Biparous and

(iii) Multiparous.

In uniparous or monochasial cyme only one lateral branch is produced below on the same side of the branch bearing it, as in Hamelia, or on opposite sides in a zigzag fashion, as in Heliotropium (B. Hatisoor). In biparous or dichasial cyme two lateral branches are formed regularly.

Jasmine, Nyctanthes (B. Sheuli), etc., are the common examples. In multiparous cyme or polychasium more than two branches are formed, e.g. Caldtropis (B. Akanda). (The multiparous cyme apparently looks like an umbel. A careful exa­mination of the position of flowers, old and young, will reveal the difference between them.)