The following points highlight the five major types of Inflorescence. The types are: 1. Solitary Flowers 2. Racemose Inflorescence 3. Cymose Inflorescence 4. Mixed Inflorescence 5. Special Inflorescence.
Type # 1. Solitary Flowers:
Flowers occur singly or are separated from other flowers of the same plant by vegetative regions. Solitary flowers are formed by direct transformation of shoot tips into flowers.
They are of two types:
(i) Solitary Terminal:
Single flowers occur at the tips of the main stem and its branches, e.g., Poppy,
(ii) Solitary Axillary:
Single flowers occur in the axils of ordinary green or foliage leaves, e.g., Petunia, Garden Nasturtium, and Shoe Flower.
Type # 2. Racemose Inflorescence:
Racemose inflorescence is an indeterminate inflorescence which shows indefinite growth and bears a number of flowers due to the presence of active growing point. The arrangement of flowers is either acropetal (older towards base and younger towards apex) or centripetal (older towards periphery and younger towards centre). Racemose inflorescence is of two types, simple and compound.
Simple Racemose Inflorescence (Fig 5.68):
Simple racemose inflorescence is that indefinite inflorescence in which the peduncle is un-branched.
It is of the following types:
1. Typical Raceme:
An un-branched elongated peduncle bears stalked or pedicellate flowers in an acropetal fashion, e.g., Larkspur (Delphinium, Fig. 5.69 A), Lupin (Lupinus), Radish (Raphanus), Linaria.
An un-branched peduncle bears pedicellate flowers in an acropetal fashion (like a typical raceme) but the pedicels of the lower flowers are longer. In this way, all the flowers come to lie at the same level, e.g., Candytuft (Iberis amara, Fig. 5.69 B).
3. Corymbose Raceme (Fig. 5.69. C):
The young flowers appear to be arranged like a corymb but in mature state the longer pedicels of the lower flowers do not bring them to the level of upper ones, e.g., Mustard.
4. Umbel (Fig. 5.70):
All the pedicellate flowers arise from a single point in a centripetal fashion because the peduncle is reduced. An involucres or a whorl of bracts is often present at the base of flowers, e.g., Androsace, Centella asiatica (= Hydrocotyle asiatica, vern. Brahmi). Umbel is also a unit of inflorescence in family Apiaceae (=Umbelliferae).
5. Spike (Fig. 5.71):
An elongated peduncle bears sessile flowers in an acropetal fashion, e.g., Chaff Flower (Achyranthes), Bottle Brush (Callistemon), Adhatoda vasica Amaranth.
6. Spikelet (Fig. 5.68):
Spikelets are small and few flowered spikes which are surrounded at the base by two scales or glumes. They occur in family Gramineae (e.g., Wheat Oat, Grass, etc.).
7. Catkin (Amentum, Fig. 5.72):
The inflorescence is a compact unisexual, often hanging, spike which matures and falls down as a single unit, e.g., Mulberry (Morns, vern. Shahtoot), Poplar (Populus), Willow (Salix), Red Hot Cattail (Acalypha hispidd), Betula, Quercus.
8. Spadix (Fig. 5.73):
It is a special type of spike which possesses a fleshy peduncle and a large green or coloured bract called spathe. The peduncle bears an upper coloured and sterile appendix. The lower part of the peduncle possesses sessile unisexual flowers, upper male and lower female.
The two types of flowers are separated by downwardly directed sterile hair or neuter flower, e.g., Colocasia, Arum. In a spadix the appendix of the peduncle and the spathe are coloured to attract insects for pollination. The spathe is tubular in the basal region to protect the flowers.
9. Capitulum or Racemose Head (Fig. 5.74):
The peduncle is somewhat flattened to form a receptacle that bears small sessile flowers called florets. The latter are of two types, tubular and ligulate. The florets are arranged in a centripetal fashion, e.g., younger towards the cenre and older towards the periphery.
The inflorescence is surrounded by one or more whorls of bracts called involucre. Capitulum inflorescence is found in family compositae, e.g., Tagetes, Zinnia, Sunflower (Helianthus annuus), Cosmos, Chrysanthe mum, Sonchus.
It may be tubular homogamous (e.g., Ageratum), ligulate homogamous (e.g., Sonchus) or heterogamous (e.g., Sunflower). In Sunflower, the central disc florets are bisexual and tubular while the peripheral ray florets are sterile or female and ligulate.
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 (Raceme of Racemes or Compound Raceme), e.g., Gold Mohur (Delonix), Cassia fistula, Asphodelus, Yucca, Neem (Azadirachta indica).
2. Compound Corymb (Corymb of Corymbs), e.g., Pyrus, Cauliflower, Candytuft. In Cauliflower (Brassica oleracea vern. hotrytis, vern. Gobhi), the flowers remain undeveloped.
3. Compound Umbel (Umbel of Umbels). Several small or daughter umbels called umbellules arise from a common point in an umbellate fashion. A whorl of bracts, called involucre, is present at the base of the parent umbel.
Similar whorls of bracts found at the bases of umbellule’s are called involucels. Compound umbel is characteristic of family umbelliferae e.g., Carrot (Daucos carota), Fennel (Foenlculum vulgare, vern. Saunf), Coriander (Coriandrum sativum, vern. Dhania).
4. Spike of Spikes, e.g., Amaranthus.
5. Compound Spadix (Spadix of Spadices), e.g., Date, Coconut.
6. Compound Capitulum (Capitulum of Capitulum) e.g., Echinops.
Type # 3. Cymose Inflorescence:
Cymose inflorescence is the name of determinate or definite inflorescence in which the tip of the main axis terminates in a flower and further growth continues by one or more lateral branches which also behave like the main axis (Fig. 5.75). The arrangement of flowers is either basipetal or centrifugal.
It is of the following types:
a. Uniparoas or Monochasial Cyme (Fig. 5.76).
The terminal bud of main axis ends in flower. A single lateral branch pushes it to one side but also itself ends in a flower. The process is repeated. The peduncle is formed by the fusion of bases of axillary branches and the main axis. It is, therefore, sympodial.
Uniparous cyme inflorescence is of two types:
(i) Helicoid (Bostryx):
All the flowers are borne on the same side forming a sort of helix, e.g., Drosera, Begonia,
(ii) Scorpioid (Cincinnus):
lowers are alternately borne on both the sides, e.g., Freesia, Tecoma, Heliotropium, Ranunculus bulbosus. A modification of scorpioid cyme is rhipidium. Here all the flowers are borne in one plane, e.g., Solanum nigrum.
b. Biparous or Dichasial Cyme (Fig. 5.77):
A terminal flower is subtended by two lateral bram.hes which also end in flowers. The process is repeated. Inflorescence axis is multipodial. e.g., Pink (Dianthus), Nyctanthes (vern. Har Singar), Spergula, Silene, Jasmine (Jasminum), Clerodendron (Clerodendrum), Bougainvillea, Teak.
c. Multiparous or Polychasial Cyme (Fig. 5.78):
More than two lateral branches continue the growth of the inflorescence when the parent axis ends in a flower. Polychasial cyme generally occurs in the primary divisions. The later divisions often become dichasial followed by monochasial ones. As in biparous cyme, the inflorescence axis is multipodial, e.g., Hamelia patens, Calotropis (vern. Ak, Madar), Asclepias.
d. Cymose Head (Glomerule):
Sessile or subsessile flowers are borne centrifugally around a receptacle, e.g., Anthocephalus cadamba (vern. Kadam), Albizia (= Albizzia), Acacia (Fig. 5.79).
Type # 4. Mixed Inflorescence:
In this case two or more types of inflorescence get mixed up to form a mixed inflorescence, e.g., panicle of spikelets (e.g., Oat, Rice), spike of spikelet’s (e.g., Wheat), corymb of capitula (e.g., Ageratum conyzoides), umbel of capitula, raceme of capitula, mixed spadix (spadices with cymose inflorescence arranged acropetally on a fleshy axis having coloured spathes, e.g., banana), thyrsus (thyrse, cymose clusters borne acrotepally on an axis, e.g., Grape Vine, male Cannabis).
Type # 5. Special Inflorescence:
a. Hypanthodium (Fig. 5.80):
Hypanthodium has a flask-shaped fleshy receptacle which possesses a narrow canal and a terminal pore at one end. The pore is surrounded by a few scales while the canal is lined by downwardly pointed hairs. Internally the receptacle bears male flowers towards the pore and female flowers towards the base.
Sterile, neuter or gall flowers occur in between the two groups. The inflorescence is formed by the condensation of three types of flower- bearing axes (cymose groups). Hypanthodium is found in the genus Ficus of the family Moraceae, e.g., Peepal (Ficus religiosa), Banyan (Ficus bengalensis), and Fig (Ficus carica).
b. Verticillaster (Fig. 5.81):
Two clusters, each having 3-9 flowers, develop on a node in the axils of opposite leaves. Each cluster consists of a dichasial cyme with monochasial branches. The axis of the cyme is shortened so that all the flowers arise from a single point.
The two opposite clusters often give the appearance of whorl or verticil due to overcrowding. The verticils are further arranged in a racemose fashion. Verticillaster inflorescence occurs in family Lamiaceae or Labiatae where stems are generally quadrangular, e.g., Ocimum sanctum (Sacred Basil, vern. Tulsi), Ocimum basilicum (Sweet Basil, vern. Niazbo), Salvia, Coleus.
c. Cyathium (Fig. 5.82):
It occurs in Poinsettia (= Euphorbia pulcherrima) and Euphorbia species. The inflorescence looks like a flower. It has a small conical receptacle surrounded by an involucre of generally five green or coloured bracts having nectariferous glands.
Internally, the inflorescence contains pedicellate achlamydeous and unisexual flowers of both the types, male and female. The female flower is single and centrally placed. Male flowers are numerous and are arranged centrifugally.
Each male flower has a pedicel and a single stamen. The joint between the two represents the thalamus. It is usually naked but in Anthostemma a whorl of small tepals or perianth occurs in this region. The female flower has similarly a pedicel and a tricarpellary pistil with lobed stigmas.