inflorescence important in flower morphology

Inflorescence

1. INFLORESCENCE By Silpa Anna Thomas Roll no:116 3 rd DC Voc Botany

2. The inflorescence is defined as the arrangement of a cluster of flowers on a floral axis. The inflorescence is of two types, they are: Racemose and Cymose. Racemose Inflorescence In this type of inflorescence, the flowers branch laterally on the floral axis. Here the floral axis keeps on growing and the flowers develop in an acropetal pattern.

3. The main characteristics of the racemose inflorescence are: Growth of the main axis (peduncle) is indefinite and continues to produce a flower bud The peduncle seldom terminates in a flower Peduncle is monopodial The first formed flowers are formed at the base of the peduncle Flowers are borne laterally in  acropetal succession, i.e. older flowers are at the base and younger ones at the tip Group of flowers are arranged centripetally, i.e. younger flowers in the middle and older flowers at the periphery Newly formed fruits are not protected by flowers Grouping of flowers is less common

4. Di fferent types of racemose inflorescence 1. Simple Raceme:  The main axis is unbranched, elongated and bears pedicellate flowers laterally in acropetal succession. The older flowers present at the base have longer stalk as compared to the upper younger flowers. Examples:  Brassica campestris  (mustard), Raphanus sativus (radish),  Crotalaria retusa ( rattleweed ),  Cleome viscosa  (Asian spiderflower ),   Antirrhinum majus  (snapdragon) etc. 2. Corymb:  In this type of inflorescence peduncle is short with pedicellate flowers. All the flowers appear at the same level. The stalk of the lower flower is longer than younger upper flowers. Example: Cauliflower

5. 3. Umbel:  The main axis is shortened. The  involucre of bracts  (whorl) is present. Flowers arise from the axil of bracts. Each flower has pedicel of the same length, spread from a common point. It can be simple umbel or  compound umbel,  which is umbel with branches, also known as  “umbel of umbels”.  Umbel inflorescence is characteristic of the Apiaceae ( Umbelliferae ) family. Examples: Simple umbel:  Centella asiatica (Brahmi),  Allium cepa  (onion),  Fatsia japonica (paper plant),  Primula veris  (cowslip), etc. Compound umbel:  Coriandrum sativum (coriander),  Foeniculum vulgare  (fennel),  Daucus carota  (carrot),  Conioselinum pacificum (parsley), etc.

6. 4. Spike:  The main axis is unbranched with unlimited growth as raceme but flowers are sessile, i.e. without pedicel, directly attached to peduncle without a stalk Examples:  Piper longum  (long pepper) ,  Acyranthes  (chaff flower) ,  Amaranthus (amaranth),  Justicia adhatoda  (Malabar nut), etc. Compound spike  is known as the  spike of spikelets.  Sessile flowers (spikelets) are present on the branched main-axis. Examples: wheat, barley, sorghum, oats etc.

7. 5. Spadix:  This is also a modified spike with a fleshy axis. It contains numerous sessile flowers arranged acropetally. The spadix is enclosed by leaf-like large, bright, colourful and curved bracts known as a “ spathe”.  Female flowers are present at the base, male and sterile flowers are present at the top. It is found in monocotyledons. Examples: Present in the plants of family Araceae (arums), Musaceae , Palmaceae In the  compound spadix,  the main axis is branched and each branch bears sessile flowers. The whole inflorescence is enclosed by one thick boat-shaped spathe. E.g. coconut Examples:  Caesalpinia  (peacock flower),  Iberis amara  (candytuft)

8. 6. Capitulum (Head):  Capitulum is also known as racemose head. It is the most advanced inflorescence. It is characteristic of the Asteraceae ( Compositae ) family. The peduncle is short, flattened and broad. Flowers are called “florets”. Florets are sessile and arranged in a centripetal manner, i.e. outer flowers are older and inner flowers are younger Individual florets are bracteate The whole inflorescence is covered with one or more whorls of bracts (involucre) Florets may be unisexual, bisexual or sterile Florets are of two types, strap-shaped  ray florets  and central tubular  disc florets If two types of florets are present in a capitulum, it is known as heterogamous If all the flowers of a capitulum are the same it is known as homogamous Examples:  Helianthus annuus  (Sunflower), Zinnia,  Tagetes erecta  (Marigold), Cosmos,  Mimosa pudica , Acacia, etc.

9. 7. Catkin:  It is a modified spike with a drooping central axis. It contains  unisexual  sessile flowers arranged closely on the peduncle. Flowers have inconspicuous petals and scaly bracts. Examples: Morus alba (mulberry), Betula (birches), Qercus (oaks), Salix (willows), etc.

10. Cymose inflorescence In this type of inflorescence, the flower is the terminating point of each floral axis. In Cymose inflorescence, flowers follow the basipetal pattern of growth

11. The growth of the main axis is limited and the lateral axis also terminates into flower and that limits the growth of the axis.   Flowers are present in the basipetal succession, i.e. older flower is present terminally and the younger ones at the base. This type of arrangement is known as centrifugal with the older flowers present in the middle and the younger ones at the periphery. Different types of Cymose inflorescence There are four main types of cymose inflorescence: Monochasial cyme Dichasial cyme Polychasial cyme Cymose capitulum

12. 1. Monochasial cyme:  It is also known as uniparous cyme. The main axis terminates in flower and it produces one lateral branch from the base, which also terminates in a flower. Each lateral and subsequent branch also produces one lateral branch with a terminal flower. Monochasial cyme is further divided into two types: Scorpioid:  Lateral branches develop alternately on both sides of the axis e.g.  Gossypium , Drosera Helicoid:  Lateral branches develop on the same side forming a helix e.g.  Begonia, Heliotropium 2. Dichasial cyme:  It is known as biparous cyme. The terminal peduncle terminates in flower. It gives rise to two lateral branches with terminal flower. Subsequent branches also behave similarly. E.g.  Jasmine, Saponaria

13. 3. Polychasial cyme:  It is known as multiparous cyme. Multiple branches arise at the base of the apical flower on the peduncle. The oldest flower is in the middle. E.g  Calotropis 4. Cymose capitulum:  In this type of arrangement the peduncle is reduced to a circular disc. The older flowers develop at the centre of the disc and the younger flowers at the periphery. This is known as centrifugal arrangement. E.g.  Acacia, Mimosa

14. The other special types of inflorescence are : Cyathium – It has a highly reduced inflorescence. It contains a cup-shaped involucre formed by the fusion of 5 bracts.  Hypanthodium  – It has a flask-shaped receptacle forming a hollow cavity. Also, it has terminal pores surrounded by scales.  Verticillaster – It is a special type of inflorescence seen in Lamiaceae . It is a condensed form of a dichasial cyme with sub-sessile or sessile flowers.  Thyrsus – it has a number of cymose clusters borne acropetally on an unlimited axis in the manner of the raceme. The example is the grapevine. Panicle – it is a branched raceme,each branch having a smaller raceme of flowers.The terminal bud of each branch continues to grow,producing more side shoots and more flowers. Eg:Lagerstroemia indica