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The arrangement of flower on the floral axis is called inflorescence.
In this type of inflorescence, the main axis continues to grow and does not terminate in a flower and give off flower laterally in an acropetal manner where old flowers are arranged toward the base and young flowers are at the tip. When peduncle is broad then flowers are centripetally arranged.
This is of following different types :
Raceme – When peduncle (main axis) is elongated and flowers are pedicellate. eg. Radish, a characteristic feature of Cruciferae family
When peduncle is branched and each branch bear pedicellated flowers like racemose and are arranged in acropetal manner known as compound raceme or panicle. eg. Gulmohar, Neem.
Spike – In it peduncle is elongated but flowers are bisexual and sessile. eg. Achyranthes,
When peduncle is branched and each branch bear spike, like inflorescence then the small branch having flower is called spikelet and this arrangement is called as spike of spikelet. Characteristic inflorescence of family gramineae.
Catkin – In it peduncle is thin, long and weak, and flowers are sessile and unisexual. Peduncle is pendulus. eg. mulberry, betula, oak.
Spadix – In it peduncle is thick, long and fleshy and have small sessile and unisexual male and female flowers covered with one or more green or colourfull bracts known as spathe. eg. Colocasia, Maize, Aroids, Palms.
Corymb – In it peduncle is short and all flowers are present at same level because the lower flower has much long pedicel than the upper one eg. Candytuft (Iberis amara).
If in this type of inflorescene peduncle is branched, then each branch has flower cluster then this type of inflorescence is called compound corymb.
eg. Cauliflower, * In mustard corymbose raceme type of inflorescence is present
Umbel – An inflorescence in which the flower stalks of different flowers are of more or less equal length, arise from the same point. At the base of flowers stalks, there is whorl of bracts forming the involucre. eg. Centella
If in this type of inflorescence, peduncle is branched then each branch has flower cluster then this type of inflorescence is called compound umbel. eg. Coriander, Foeniculum, Cuminum. Characteristic feature of umbeliferae.
* Scapigerous umbel is found in onion
Capitulum / Racemose head – In it the growth of peduncle is retarded and it becomes broad, flattened concave or convex. On it, small flowers are found. These flowers are called floret. If all the flower of capitulum is same, then it is called homogamous. If two different type of floret, ray floret and disc floret are present in same inflorescence than it is known as heterogamous. In this type of inflorescence, florets may be unisexual, bisexual and sterile. This inflorescence is surrounded by one or more involucre. It is most advanced type of inflorescence. eg. Sunflower, Zinnia, Marigold, Cosmos.
Characteristic feature of asteraceae family.
In this type of inflorescence, the peduncle terminate in a flower. In it, the older flowers are present at tip and young buds are arranged towards base. This arrangement is called basipetal succession. It is of following types.
Uniparous cyme / Monochasial cyme – The peduncle ending in a flower producing lateral branch at a time of ending in flower. It is of two types –
- Helicoid cyme – When all lateral branches developed on the same side on peduncle then it is called helicoid cyme. eg. Heliotropium, Saraca, Atropa, Datura.
- Scorpioid cyme – In it the lateral branch is alternately develop on left and right side. eg. Bignonia,
- Riphidium – In monochasial cyme all flowers are borne on same plane. eg. Solanum nigrum
- Dichasial or biparous cyme – In it peduncle ends in a flower, from the basal part of peduncle two lateral branches arise, which also end in a flower, now this same arrangement occur on these lateral branches. eg. Bougainvillaea, Jasmine, Teak, Mirabilis, Dianthus, Nyctanthes.
- Multiparous cyme / polychasial – In it peduncle ends in a flower and from the base of it many lateral branches arise which also terminates in flower, this arrangement now also occur on these lateral branches. eg. Calotropis (Madar), Nerium, Asclepias, Hamelia.
SPECIAL TYPE OF INFLORESCENCE
Cyathium – The bracts or the involucre become fused to form a cup-shaped structure on the margin. In the central part of cup-shaped structure, a single female flower is found, which mature earlier. Due to the growth of pedicel, this comes out from the cup-shaped structure. Female flowers are surrounded by large no. of small male flowers. The male flower, which lies toward centre mature earlier than the flower which is towards periphery. This inflorescence is found in Euphorbiaceae family like Euphorbia, Poinsettia, Pedilanthus.
Verticillaster – A cluster of subsessile or sessile 3-9 flowers born on a dichasial cyme ending in monochasial cyme (scorpioid) in the form of condensed whorl on either side of the node. The opposite clusters give the appearance of whorl or verticel due to overcrowding. The verticels are further arranged in a racemose manner eg. Ocimum (Tulsi), Salvia. Characteristic inflorescence of labiateae family.
Hypanthodium – In it peduncle is modified in narrow cup-like structure. At the base of cup female flowers develop while towards mouth male flower develops. All three types of flowers are present in this inflorescence. eg. Banyan, Peepal, Ficus species.
Coenanthium: In Dorsitenia, the receptacle becomes saucer-shaped and its margins are slightly curved. Arrangement of florets is similar to hypanthodium.
Mixed inflorescence – Some times flowers are arranged in both racemose and cymose manner on same peduncle called mixed inflorescence.
- Mixed spadix – Banana
- Cymose raceme or thyrsus – Grapes.