The Inflorescences Definition of the inflorescence An inflorescence is now generally accepted to be the arrangement of flowers on the floral axis and their branching system.

Types of the inflorescence The present system of inflorescence classification distinguishes three major types, racemose, cymose and mixed according to the branching of the flower axis. However, there are some special types of inflorescence that can hardly be distinguished by the branching mode of the axis.

I- Racemose or Indeterminate In the racemose (Indeterminate) inflorescences, the branching of the main axis (peduncle) is monopodial, thus the youngest flower is close to the apical bud and the progression of blooming is downward or inward. The following eight types of racemose inflorescences are recognized:

(1) Simple raceme: Flowers are stalked and arranged on an erect peduncle with internodes in between e.g. Antirrhinum. Compound raceme is common and is called panicle, however, some panicles may be cymes.

(2) Spike: Flowers are sessile on erect peduncle, no or very short internodes, e.g. Plantago. In compound spikes, each branch forms a simple spike known as spikelet, e.g. members of family Graminae (Poaceae).

(3) Catkin: Like the simple spike but axis is weak and hanging downward e.g. Salix.

(4) Spadix: Like the spike but with a fleshy axis. Flowers are often unisexual and enveloped by a large bract called spathe, e.g. Calla. (5) Corymb: It is like a simple raceme but lower (older) flowers having longer stalks so that all flowers are at the same level. Compound Corymb appears to be more common than simple e.g. Iberis. (6) Umbel: Like the corymb but the internodes are greatly reduced so that; flowers appear to arise from one point. Compound umbels are very common, e.g. members of the family Umbelliferae (Ammiaceae).

(7) Capitulum: Flowers sessile on a flat, concave or convex horizontal peduncle. Flowers are often unisexual and the head is usually subtended by a number of bracts known as involucre, e.g. members of the family Asteraceae

(8) Head: Flowers sessile on spherical peduncle. The head is usually subtended by a number of bracts known as involucre, e.g. members of the family Luguminosae.

II- Cymose or Determinate In cymose inflorescence, branching is sympodial, i.e. the oldest flower terminates the main axis and the growth is continued by lateral buds. The propagation of blooming is downward or outward.

1-Simple raceme Panicle 2-Spike 3- Catkin

4-Spathe 5-Corymb Compound Corymb

6- Umbel Compound Umbel 7-Capitulum Three main types of cymose inflorescence recognized:

(1) Monochasium: The terminal bud forms a flower and a single lateral bud give rise to a younger flower. In compound monochasium there are more than two flowers on the sympodial peduncle. When flowers develop on both sides the inflorescence is termed scopoid, e.g. Linum, and if all flowers develop on one side, the inflorescence is termed helicoid e.g. members of family Boraginaceae.

(2) Dichasium: The terminal bud forms a flower and from the axis of two opposite bracts arise two younger flowers on both sides. This arrangement can be repeated leading to the formation of a compound dichasium, e.g. Gypsophila.

(3) Polychasium: The terminal bud forms a flower and more than two flowers develop at the same point on the peduncle. Thus, the middle oldest flower is surrounded by several younger flowers. It resembles an umbel, but the latter have the younger flower in the center e.g. Pelargonium. Some cymose inflorescences resemble indeterminate flowers such as umbel head and panicles.

III- Mixed inflorescences: In a mixed inflorescence, the main axis carries lateral branches in indeterminate fashion like racemose inflorescences, but lateral branches carry flowers in a determinate fashion as cymose inflorescence. In a thyrse, a branched inflorescence in which the main axis is indeterminate and the lateral branches determinate in their growth.

IV- Special types of inflorescence:

(1) Cyathium: is composed of cup shaped involucre provided with nectar secretary glands and comprises female flowers, in the center composed of one pistil surrounded by a number of reduced male flowers represented by solitary stamen e. g. Euphorbia (2) Hypanthium (Syconium): is composed a fleshy receptacle enclosing a hollow cavity leaving a special pore. In this cavity large number of minute flowers are borne on the inner wall of the cavity. Female flowers develop at the base of the cavity and the female flowers towered the top e.g. Ficus. (3) Verticilate: It is consisting of dichasial condensed sessile type surrounding the main axis at the nodes e. g. Mentha and other members of the Labiatae (Lamiaceae)

Gland Ovary Male flower

Gynophore

1-Cyathium 3-Syconium 3-Verticillate

Illustration and photographs for the special types of inflorescences