Type of inflorescences

 Inflorescence is the arrangement of flowers on the floral axis. The stalk bearing an inflorescence is called peduncle. It arises terminally or in axil and may have a number of flowers. Inflorescence has been classified into two types, viz. racemose and cymose. Besides, there is also a special type of inflorescence, which does not fit into these groups. 

A. Racemose Inflorescence In this type of inflorescence the main axis is unlimited in growth, branched or unbranched. It never terminates into a flower and bears flowers in acropetal succession. The main types are: 

1. Raceme: The main axis, which is elongated, bears stalked flowers, e.g. Brassica (mustard), Raphanus (radish), and dwarf gulmohar.

 2. Spike: This is like raceme but the flowers are sessile or unstalked, e.g. Adhatoda, Achyranthes (chaff-flower).

 3. Spikelet: Very small spike with one or few flowers called florets. Each spikelet has two sterile glumes and one fertile glume-bearing flower called lemma. One bracteole is present just opposite to lemma called palea. Each flower of the spikelet is enclosed by the lemma and palea. Flowers and glumes are arranged in two opposite rows on the spikelet, e.g. paddy (Oryza sativa), wheat (Triticum), and grasses. 

4. Catkin: This is like a spike but differs from latter in having a long and pendulous axis, usually bearing unisexual flowers, e.g. mulberry (Morus alba), Betula and oak.

 5. Spadix: This is a spike with fleshy axis enclosed by one or several large and brightly coloured bracts, called the spathes. Usually female flowers borne at the base and male flowers above, e.g. Musa paradisiaca (banana), Colocasia (aroids). 

6. Corymb: Here the axis is not elongated. It is short and bears stalked flowers in such a manner that they are placed almost at the same level, e.g. candytuft, Lantana. 

7. Umbel: This differs from corymb in having a very shortened and suppressed axis. Flowers have stalks of equal length and form a cluster. It is umbrella like in appearance, e.g. coriander, carrot. 

8. Head or Capitulum: The main axis is a flattened, more or less convex structure, the receptacle, on which the florets (small-flowers) . The whole inflorescence is surrounded by an involucre (a whorl of bracts) and bears only one or two types of flowers: inner disc florets and outer ray florets. The disc florets are usually bisex 

ual whereas the ray florets are unisexual (pistillate) or neuter, e.g. sunflower, zinnia, and marigold. 

Compound Racemose It is an indefinite or indeterminate inflorescence in which the peduncle is branched in a racemose fashion with each branch bearing flowers in acropetal or centripetal fashion.

 1. Panicle: Here the main axis (rachis) is branched. It is also called compound raceme e.g. gold mohur (Delonix), amaltas (Cassia fistula), neem (Azadirachta indica).

 2. Compound corymb: It is a modified corymb. The central axis or rachis is branched and the flowers are borne on these branches in corymb-like manner. It is also called corymb of corymbs, e.g. Pyrus, cauliflower, and candytuft. In cauliflower (Brassica oleracea var. botrytis), the flowers remain undeveloped.

 3. Compound umbel: It is modified umbel where inflorescence axis is branched. The branches arise from a single point in exactly umbel-like manner. These branches bear umbels, which are known as umbellules. A whorl of bracts, called involucre, is present at the base of the parent umbel. Similar whorls of bracts found at the bases of umbellules are called involucels. It is also called umbel of umbels. Compound umbel is characteristic of family umbelliferae, e.g. carrot (Daucus carota), fennel (Foeniculum vulgare, vern. saunf), coriander (Coriandrum sativum, vern. dhania). 

B. Cymose Inflorescence In this type the main axis is always limited in growth and terminates into a flower. They are usually stalked, and borne in a basipetal order. The main types are: 1. Uniparous or monochasial cyme: Here the main axis terminates into a flower and one lateral branch axis develops from its base, which also ends in a flower. There are two types of monochasial cyme: (a) Scorpioid type in which the lateral branches of the axis bearing a terminal flower alternate as in Ranunculus bulbosus, and (b) helicoid type in which each lateral branch bearing a terminal flower develops on the same side forming a helix as in Heliotropium. 

2. Biparous or dichasial cyme: Here two lateral branches develop, on either side of the terminal flower. The lateral branches may again branch similarly, e.g. jasmine (Jasminum), pink (Dianthus).

 3. Multiparous or polychasial cyme: Here more than two lateral branches arise from the base of the apical flower, e.g. madar (Calotropis). 

Special type of inflorescences

1. Hypanthodium: Here the main axis forms a cup-shaped receptacle with a small opening at the top. Flowers are enclosed within the cup in cymose groups. They are unisexual; male flowers are near the ostiole and fertile female flowers at the base of the cup, e.g. fig (Ficus), etc. 

 2. Cyathium: It is a compound inflorescence which looks like a flower. Here the cupshaped structure is formed by the involucre. The reduced flowers (without perianth) are placed on a receptacle. There is one central female flower represented by a single pistil. This is surrounded by a large number of male flowers each represented by a single stamen only. The stalked flowers are subtended by a bracteole. There are also nectar glands on the cup, e.g. Euphorbia. Fig. 5.28 Cyathium inflorescence 

3. Verticillaster: Here one inflorescence consisting of two clusters develops from each of the two opposite axils of the leaves. Each cluster is a dichasial cyme reduced to two scorpioids. Flowers are sessile and appear in a false whorl or vertically around the stem. It is characteristic of the family Labiatae as in sacred basil (Ocimum sanctum), Coleus.