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In recemose inflorescence
Main axis continues to grow, The flowers develop in acropetal succession , Opening of flower is centripetal
But according to definition
Acropetal succession : flowers opening in succession from base to apex
Centripetal : the younger flowers are towards the centre and the older towards the outside…
I can't understand that if lower flowers or flowers towards centre open first then they should be older but according to above statement flowers at base are younger. Is there other concept that I don't know?
Inflorescence is a flowering shoot that bears more than one flower. There are two types of inflorescence Cymose and Racemose. Of the two types of inflorescence Cymose inflorescence is more primitive and Racemose is derived. (Parkin 1914)
In this type of inflorescence the main axis does not end in a flower, but it grows continuously and develops flowers on its lateral sides in acropetal succession (acropetal (adj.) - of leaves or flowers; developing or opening in succession from base to apex ).
Acropetal sucession is observed in raceme, the simplest racemose inflorescence.
Now Capitulum or Head, it is another type of racemose inflorescence in which
the main axis or receptacle becomes suppressed, and almost flat, and the flowers (also known as florets) are sessile (without stalk) so that they become crowded together on the flat surface of the receptacle. The florets are arranged in a centripetal manner on the receptacle, i.e., the outer flowers are older and open earlier than the inner ones.
In the following L.S. of sunflower you can see the disc florets developing/opening in centripetal manner.
P.S. I'm not a botanist but a candidate of B.Sc Zoology. I had Botany as my additional subject so I answered it from my knowledge.
What is Racemose Inflorescence? Describe briefly the various types of Racemose Inflorescence?
In this type of inflorescence, the main axis does not end in a flower, but it grows continuously and develops flowers on its lateral sides in acropetal succession (i.e the lower or outer flowers are older than the upper or inner ones). The various forms of racemose inflorescence may be described under three heads. They are as follows-
- With the main axis elongated- raceme, spike, spikelets, catkin, spadix.
- With the main axisshortened- corymb, umbel.
- With the main axisflattened- capitulum or head.
The elongated main axis bears pedicellate flowers in an acropetal order. Example- Dog Flower (Antirrhinum), Radish (Raphanus Sativus), Turnip, Dwarf Gulmohar (Caesalpinia), Mustard (Brassica Campestris), Larkspur. When the main axis of raceme is branched and the lateral branches bear the flowers, the inflorescence is known as compound raceme or panicle. Example- Cassia Fistula, Delonix Regia, Margosa, Neem (Azadirachta Indica).
The elongated main axis bears sessile bisexual flowers in an acropetal manner. Example- Bottle Brush (Callistemon), Latjira (Achyranthes Aspera), Adhatoda, Spinach, Amaranthus.
It is small and a few-flowered spike which is covered by two scales called glumes. Spikelet is basic inflorescence in the grass family Poaceae.
Catkin or Amentum:
It has an elongated spike possessing unisexual and apetalous flowers. Example- Oak (Quercus), Mulberry (Morus), Willow (Salix), Betula (Birch), Poplar (Populus).
The inflorescence is like a spike which is covered by one to a few large bracts called spathes. The peduncle is thick and fleshy which bears unisexual flowers except in the apical region. The sterile region is called the appendix. It is coloured in aroids. In aroids the spathe is single. It forms a tube in the lower half to cover and protect the flowers. The flowers are sessile, generally male towards the upper side, female towards the lower side and downwardly pointed hair or neuter flowers in the middle. Example- Colocasia, Cobra Plant (Arisaema). In Cobra Plant the male and female flowers are formed in separate spadices. Both the spathe and the appendix are bent to appear like the head of a snake. In Maize, the female inflorescence is a spadix having a number of spathes.
The main axis is shortened, broad and flat. The old flowers at the lower levels on the axis have longer pedicles than the upper ones so that all the flowers reach more or less to the same level. Example- Candytuft (Iberis Amara), Cassia Sophera.
In this inflorescence, the primary axis remains comparatively short, and it bears at its tip a group of flowers which possess pedicels or stalks of more or less equal lengths so that the flowers are seen to spread out from a common point. In this inflorescence, a whorl of bracts forming an involucre is always present, and each individual flower develops from the axil of a bract. Generally, the umbel is branched and is known as umbel of umbels (Compound Umbel), and the branches bear flowers. Example- Coriander (Coriandrum Sativum), Fennel, Carrot. Sometimes, the umbel is unbranched and known as a simple umbel. Example- Brahmi (Centella Asiatica), Androsace. Umbel inflorescence is the basic inflorescence of coriander family Apiaceae or Umbelliferae.
Capitulum or Head:
The peduncle is flattened like a flat, convex or concave disc. It bears small, sessile flowers or florets over its upper surface in centripetal fashion with younger towards the centre and older towards the periphery. The whole inflorescence is covered by one or more whorls of involucre or bracts. Bracts may also occur at the base of individual florets. Florets are of two types, tubular and ligulate. Capitulum can be tubular homogamous (example- Ageratum), ligulate homogamous (example- Sonchus) or heterogamous having tubular flowers on the central platform and ligulate flowers on the periphery (example- Sunflower). Capitulum inflorescence is a typical inflorescence of family Asteraceae or Compositae. Example- Dahila, Cosmos, Zinnia, Tagetes, Aster. In Compound Capitulum, many daughter capitula arise from a flattened receptacle of mother capitulum. Example- Echinops.
The arrangement of solitary flower or a group of flowers on the specialized floral axis or peduncle is known as inflorescence or anthotaxy. An inflorescence is categorized on the basis of the arrangement of flowers on a main axis and by the timing of its flowering.
Description of Inflorescence
In the flowering plants (angiosperms) the flowers are the sexual reproductive organs and they develop from specialized floral buds remaining at the axils of leaves or at the apices of shoots. The axillary floral buds develop into solitary axillary flowers (e.g., chinarose), while the apical bud forms the solitary terminal flowers (e.g., Datura). But sometimes the flowers may remain in an aggregated condition and the arrangement of flowers on the floral stalk or peduncle is known as inflorescence.
Sometimes flowers directly come up from the peduncle or sometimes they are borne on minute stalks called pedicels. The growth of the peduncle may be indefinite, i.e., flowers arising in acropetal succession from base to apex and it is called racemose inflorescence. Sometimes the stalk of racemose inflorescence may grow beyond the flowers and it is called rachila, (e.g., grass). In some cases, the racemose stalk is secluded by spathy bracts and it is called spadix (e.g., Musa). Sometimes the inflorescence stalk may form a flattened, fleshy, expanded structure called receptacle and the flowers are arranged on it, it is called capitulum (e.g., sunflower). The inflorescence stalk of underground modified stem like the bulb of onion is a fat stem called scape.
The inflorescence usually emerge from the aerial shoot and it is termed as cauliflory or cladanthy (e.g., Jackfruit), it is of two types viz.,
(i) Inflorescence stalks directly emerging from trunk called trunciflory (e.g., papaw).
(ii) Inflorescence stalks arising from the aerial branches e.g., Ixora.
Sometimes the inflorescence stalks may be borne on the leaves or lamina and called epiphyllous inflorescence (e.g., Begonia).The inflorescence stalk may sometimes be delimited with a terminal flower and it is called cymose inflorescence (e.g., Heliotropium), in this case, the flowers appear in basipetal succession, i.e., the terminal flower is first matured followed by the lower flowers.
Structure of Inflorescence
i) The inflorescence may be represented by a single flower or a group of flowers.
ii) The inflorescence stalk is called peduncle or rachis and the stalks of individual flowers are called pedicels.
iii) There are two main types of inflorescences, viz., the determinate or cymose and the indeterminate or racemose.
iv) Sometimes the inflorescence may be mixed, that means, with both racemose and cymose characters.
v) There are also some special types of condensed cymose inflorescences.
vi) The rachis may be simple or un-branched, as in spike or branched or compound panicle.
vii) The rachis may be subtended by a basal bract-like structure and called bracteate (e.g., Adhatoda) or sometimes it may be without bract and called ebracteate e.g., Amaranthus.
viii) Sometimes there may be bracteoles present at the base of individual flowers e.g., lemma and palea of spikelet of rice.
ix) In some cases, the inflorescence are never exposed, rather they remain covered within the receptacle.
x) At times, the flowers may be without pedicel or sessile in nature.
Classification of Inflorescence
There are four major types of inflorescences, those are:
i) Racemose or indefinite
ii) Cymose or definite
iii) Mixed type
iv) Special cymose.
Racemose inflorescence ( indefinite inflorescence )
A type of flowering shoot (see inflorescence ) in which the growing region at the tip of the flower stalk continues to produce new flower buds during growth. As a result, the youngest flowers are at the top and the oldest flowers are at the base of the stalk. In a flattened inflorescence, the youngest flowers are in the centre and the oldest flowers are on the outside. Types of racemose inflorescence include the . .
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DEFINITIONS AND KEY POINTS OF MORPHOLOGY
-The inflorescence in which branching of the main axis or peduncle is racemose or cymose is called simple inflorescence.
‘Elie inflorescence in which main axis develops lateral flowers and continues to grow indefinitely upto last flower is called
In this inflorescence the mMa a xis soon ends in a flower It gives one or two laterd branches or daughter axis, each of which ends in th is process repeated several times.
The racemose inflorescence in which main axis is elongated and bears lateral pedicillate flowers is called simple raceme.
The inflorescence in which main axis is elongated and bears sessile lateral flowers is called spike.
The spike with unisexual flowers is called catkin.
The unisexual spike with a large and
membranous bract is called strobilus.
The special type of spike with main axis thick and fleshy bearing unisexual flowers is called spad ix.
The inflorescence in which main axis flattened to form receptacle and flowers are crowed on it is called capitulum.
The compact globose inflorescence having groups of sessile scorpioid cytnes is called
The inflorescence in which main axis is branched and bears flowers in the same manner is called compound inflorescence.
The ripened ovary containing seeds is called fruit.
The fruits formed from a single flower with gynoecium monocarpellary or polycarpillary
and syncarpous is called simple fruit.
The dry, one seeded and indehiscent fruit is called achenial fruit.
Achene: The achenial fruit in which pericarp is membranous or leathery and free from seed coat or testas called achene.
The dry. many seeded and dehiscent fruit is called cal .sular fruit.
The fruit formed from monocarpellary pistil and cf,hiscence along both dorsal and ventral sutures is called legume.
The fruit derived from polycarpillary,
syncarpous pistil with superior ovary is called capsule
The dry. many seeded fruits which break into a number of one seeded parts on ripening is called shizocarpic fruit.
The legume or pod modified by the formation of fidse septum and constrictions is called
The fruit developed from multi locular ovary with each locule having single seed and
ripened fruit break up into a number of one seeded dehiscent parts called cocci is called
The fruit In w hich splits longitudinally between the loculi into two one seeded mericarps which remains attached to central axis
carpohore is called cremocarp.
Drupes: The succulent fruit in which mesocarp forms the edible portion of fruit and endocarp forms a hard shell or stone is called drupe.
The indehiscent many seeded fleshy fruit in which mesocarp and endocarp forms pulp is called berries.
The fruit in which outer skin and edible portion of the fruit are formed from thalamus and carpel develops central cartilaginous core is called pome.
The composite fruit formed from a hollow
pear shaped hypanthodium inflorescence is cal led sycon us.
The bulb in which leaves overlap each other at their margins is called imbricate bulb.
The bulb in which leaves surround each other is called tunicated bulb.
The smollen underground tips of branches of vertical axis which store food and use for vegetative propagation is called stem tuber.
Phylloclades are composed of more than one internode. .
cladodes are composed of single internode.
Leaves are gredi flat structures borne on the stem or on th.: britches.
The special leaf in the axil of which flower
One or two leave present on the stalk of flower are called bra. teoles.
Pair of outgrowths eceloped at the base of petiole of a leaf are . ailed stipules. The stipule like strum’ es present at base of leaflets of a compund leaf are called stiples.
The arrangement of the leaves on the stem is called ph llotaxis.
The arrangement of veins and vein lets in the lamina of a leaf is called venation.
citation in he Ii smaller veins arise from the midrib and form nem ork is called reticulate citation.
It means of equal size run parallel to eaeli other limp the base to apex or midrib to margin Heal is called parallel citation..
Inflorescences are described by many different characteristics including how the flowers are arranged on the peduncle, the blooming order of the flowers and how different clusters of flowers are grouped within it. These terms are general representations as plants in nature can have a combination of types. These structural types are largely based on natural selection. 
Inflorescences usually have modified foliage different from the vegetative part of the plant. Considering the broadest meaning of the term, any leaf associated with an inflorescence is called a bract. A bract is usually located at the node where the main stem of the inflorescence forms, joined to the rachis of the plant, but other bracts can exist within the inflorescence itself. They serve a variety of functions which include attracting pollinators and protecting young flowers. According to the presence or absence of bracts and their characteristics we can distinguish:
- Ebracteate inflorescences: No bracts in the inflorescence.
- Bracteate inflorescences: The bracts in the inflorescence are very specialised, sometimes reduced to small scales, divided or dissected.
- Leafy inflorescences: Though often reduced in size, the bracts are unspecialised and look like the typical leaves of the plant, so that the term flowering stem is usually applied instead of inflorescence. This use is not technically correct, as, despite their 'normal' appearance, these leaves are considered, in fact, bracts, so that 'leafy inflorescence' is preferable.
- Leafy-bracted inflorescences: Intermediate between bracteate and leafy inflorescence.
If many bracts are present and they are strictly connected to the stem, like in the family Asteraceae, the bracts might collectively be called an involucre. If the inflorescence has a second unit of bracts further up the stem, they might be called an involucel.
Ebracteate inflorescence of Wisteria sinensis
Bracteate inflorescence of Pedicularis verticillata.
Leafy-bracted inflorescence of Rhinanthus angustifolius.
Terminal flower Edit
Plant organs can grow according to two different schemes, namely monopodial or racemose and sympodial or cymose. In inflorescences these two different growth patterns are called indeterminate and determinate respectively, and indicate whether a terminal flower is formed and where flowering starts within the inflorescence.
- Indeterminate inflorescence: Monopodial (racemose) growth. The terminal bud keeps growing and forming lateral flowers. A terminal flower is never formed.
- Determinate inflorescence: Sympodial (cymose) growth. The terminal bud forms a terminal flower and then dies out. Other flowers then grow from lateral buds.
Indeterminate and determinate inflorescences are sometimes referred to as open and closed inflorescences respectively. The indeterminate patterning of flowers is derived from determinate flowers. It is suggested that indeterminate flowers have a common mechanism that prevents terminal flower growth. Based on phylogenetic analyses, this mechanism arose independently multiple times in different species. 
In an indeterminate inflorescence there is no true terminal flower and the stem usually has a rudimentary end. In many cases the last true flower formed by the terminal bud (subterminal flower) straightens up, appearing to be a terminal flower. Often a vestige of the terminal bud may be noticed higher on the stem.
Indeterminate inflorescence with a perfect acropetal maturation.
Indeterminate inflorescence with an acropetal maturation and lateral flower buds.
Indeterminate inflorescence with the subterminal flower to simulate the terminal one (vestige present)
In determinate inflorescences the terminal flower is usually the first to mature (precursive development), while the others tend to mature starting from the bottom of the stem. This pattern is called acropetal maturation. When flowers start to mature from the top of the stem, maturation is basipetal, while when the central mature first, divergent.
Determinate inflorescence with acropetal maturation
Determinate inflorescence with basipetal maturation
Determinate inflorescence with divergent maturation
As with leaves, flowers can be arranged on the stem according to many different patterns. See 'Phyllotaxis' for in-depth descriptions
Similarly arrangement of leaf in bud is called Ptyxis.
When a single or a cluster of flower(s) is located at the axil of a bract, the location of the bract in relation to the stem holding the flower(s) is indicated by the use of different terms and may be a useful diagnostic indicator.
Typical placement of bracts include:
- Some plants have bracts that subtend the inflorescence, where the flowers are on branched stalks the bracts are not connected to the stalks holding the flowers, but are adnate or attached to the main stem (Adnate describes the fusing together of different unrelated parts. When the parts fused together are the same, they are connately joined.)
- Other plants have the bracts subtend the pedicel or peduncle of single flowers.
Metatopic placement of bracts include:
- When the bract is attached to the stem holding the flower (the pedicel or peduncle), it is said to be recaulescent sometimes these bracts or bracteoles are highly modified and appear to be appendages of the flower calyx. Recaulescences is the fusion of the subtending leaf with the stem holding the bud or the bud itself,  thus the leaf or bract is adnate to the stem of flower.
- When the formation of the bud is shifted up the stem distinctly above the subtending leaf, it is described as concaulescent.
Flower and subtending bract
Lilium martagon (flower and subtending bract)
There is no general consensus in defining the different inflorescences. The following is based on Focko Weberling's Morphologie der Blüten und der Blütenstände (Stuttgart, 1981). The main groups of inflorescences are distinguished by branching. Within these groups, the most important characteristics are the intersection of the axes and different variations of the model. They may contain many flowers (pluriflor) or a few (pauciflor). Inflorescences can be simple or compound.
Simple inflorescences Edit
Indeterminate or racemose Edit
Indeterminate simple inflorescences are generally called racemose / ˈ r æ s ɪ m oʊ s / . The main kind of racemose inflorescence is the raceme ( / ˈ r æ s iː m / , from classical Latin racemus, cluster of grapes).  The other kind of racemose inflorescences can all be derived from this one by dilation, compression, swelling or reduction of the different axes. Some passage forms between the obvious ones are commonly admitted.
- A raceme is an unbranched, indeterminate inflorescence with pedicellate (having short floral stalks) flowers along the axis.
- A spike is a type of raceme with flowers that do not have a pedicel.
- A racemose corymb is an unbranched, indeterminate inflorescence that is flat-topped or convex due to their outer pedicels which are progressively longer than inner ones.
- An umbel is a type of raceme with a short axis and multiple floral pedicels of equal length that appear to arise from a common point. It is characteristic of Umbelliferae.
- A spadix is a spike of flowers densely arranged around it, enclosed or accompanied by a highly specialised bract called a spathe. It is characteristic of the family Araceae.
- A flower head or capitulum is a very contracted raceme in which the single sessile flowers share are borne on an enlarged stem. It is characteristic of Dipsacaceae.
- A catkin or ament is a scaly, generally drooping spike or raceme. Cymose or other complex inflorescences that are superficially similar are also generally called thus.
Determinate or cymose Edit
Determinate simple inflorescences are generally called cymose. The main kind of cymose inflorescence is the cyme (pronounced 'saim', from the Latin cyma in the sense ‘cabbage sprout’, from Greek kuma ‘anything swollen’).   Cymes are further divided according to this scheme:
- Only one secondary axis: monochasium
- Secondary buds always develop on the same side of the stem: helicoid cyme or bostryx
- The successive pedicels are aligned on the same plane: drepanium
- The successive pedicels are arranged in a sort of spiral: cincinnus (characteristic of the Boraginaceae and Commelinaceae)
- The successive pedicels follow a zig-zag path on the same plane: rhipidium (many Iridaceae)
- Secondary axis still dichasial: dichasium (characteristic of Caryophyllaceae)
- Secondary axis monochasia: double scorpioid cyme or double helicoid cyme
Bostryx (lateral and top view)
Drepanium (lateral and top view)
Cincinnus (lateral and top view)
Rhipidium (lateral and top view)
A cyme can also be so compressed that it looks like an umbel. Strictly speaking this kind of inflorescence could be called umbelliform cyme, although it is normally called simply 'umbel'.
Another kind of definite simple inflorescence is the raceme-like cyme or botryoid that is as a raceme with a terminal flower and is usually improperly called 'raceme'.
Berberis vernae (botryoid)
A reduced raceme or cyme that grows in the axil of a bract is called a fascicle. A verticillaster is a fascicle with the structure of a dichasium it is common among the Lamiaceae. Many verticillasters with reduced bracts can form a spicate (spike-like) inflorescence that is commonly called a spike.
Compound inflorescences Edit
Simple inflorescences are the basis for compound inflorescences or synflorescences. The single flowers are there replaced by a simple inflorescence, which can be both a racemose or a cymose one. Compound inflorescences are composed of branched stems and can involve complicated arrangements that are difficult to trace back to the main branch.
A kind of compound inflorescence is the double inflorescence, in which the basic structure is repeated in the place of single florets. For example, a double raceme is a raceme in which the single flowers are replaced by other simple racemes the same structure can be repeated to form triple or more complex structures.
Compound raceme inflorescences can either end with a final raceme (homoeothetic), or not (heterothetic). A compound raceme is often called a panicle. Note that this definition is very different from that given by Weberling.
Compound umbels are umbels in which the single flowers are replaced by many smaller umbels called umbellets. The stem attaching the side umbellets to the main stem is called a ray.
Homeothetic compound raceme
Melilotus officinalis (homoeothetic compound raceme)
Heterothetic compound raceme
Hebe albicans (heterothetic compound raceme)
The most common kind of definite compound inflorescence is the panicle (of Webeling, or 'panicle-like cyme'). A panicle is a definite inflorescence that is increasingly more strongly and irregularly branched from the top to the bottom and where each branching has a terminal flower.
The so-called cymose corymb is similar to a racemose corymb but has a panicle-like structure. Another type of panicle is the anthela. An anthela is a cymose corymb with the lateral flowers higher than the central ones.
A raceme in which the single flowers are replaced by cymes is called a (indefinite) thyrse. The secondary cymes can be of any of the different types of dichasia and monochasia. A botryoid in which the single flowers are replaced by cymes is a definite thyrse or thyrsoid. Thyrses are often confusingly called panicles.
Other combinations are possible. For example, heads or umbels may be arranged in a corymb or a panicle.
Achillea sp. (heads in a corymb)
Hedera helix (umbels in a panicle)
The family Asteraceae is characterised by a highly specialised head technically called a calathid (but usually referred to as 'capitulum' or 'head'). The family Poaceae has a peculiar inflorescence of small spikes (spikelets) organised in panicles or spikes that are usually simply and improperly referred to as spike and panicle. The genus Ficus (Moraceae) has an inflorescence called syconium and the genus Euphorbia has cyathia (sing. cyathium), usually organised in umbels.
Triticum aestivum (compound spikes, "spikes")
Oryza sativa (spikes in a panicle, "panicle")
Genetic basis Edit
Genes that shape inflorescence development have been studied at great length in Arabidopsis. LEAFY (LFY) is a gene that promotes floral meristem identity, regulating inflorescence development in Arabidopsis.  Any alterations in timing of LFY expression can cause formation of different inflorescences in the plant.  Genes similar in function to LFY include APETALA1 (AP1). Mutations in LFY, AP1, and similar promoting genes can cause conversion of flowers into shoots.  In contrast to LEAFY, genes like terminal flower (TFL) support the activity of an inhibitor that prevents flowers from growing on the inflorescence apex (flower primordium initiation), maintaining inflorescence meristem identity.  Both types of genes help shape flower development in accordance with the ABC model of flower development. Studies have been recently conducted or are ongoing for homologs of these genes in other flower species.
Environmental influences Edit
Inflorescence-feeding insect herbivores shape inflorescences by reducing lifetime fitness (how much flowering occurs), seed production by the inflorescences, and plant density, among other traits.  In the absence of this herbivory, inflorescences usually produce more flower heads and seeds.  Temperature can also variably shape inflorescence development. High temperatures can impair the proper development of flower buds or delay bud development in certain species, while in others, an increase in temperature can hasten inflorescence development.   
Meristems and inflorescence architecture Edit
The shift from the vegetative to reproductive phase of a flower involves the development of an inflorescence meristem that generates floral meristems.  Plant inflorescence architecture depends on which meristems becomes flowers and which become shoots.  Consequently, genes that regulate floral meristem identity play major roles in determining inflorescence architecture because their expression domain will direct where the plant's flowers are formed. 
On a larger scale, inflorescence architecture affects quality and quantity of offspring from selfing and outcrossing, as the architecture can influence pollination success. For example, Asclepias inflorescences have been shown to have an upper size limit, shaped by self-pollination levels due to crosses between inflorescences on the same plant or between flowers on the same inflorescence.  In Aesculus sylvatica, it has been shown that the most common inflorescence sizes are correlated with the highest fruit production as well. 
Some species have flower and inflorescence intermediates. In these cases, some reproductive structures of certain flowers appear as transitional between inflorescences and flowers, making it difficult to accurately categorize and identify the structure as one or the other. For example, plants of the genus Potamogeton have inflorescences that appear to be single flowers. 
Doc: Flower Inflorescence NEET Notes | EduRev
What is Inflorescence?
The arrangement of flower on floral axis is called inflorescence.
A flower is a significant part of a plant tailored for reproduction. In addition, it is an essential part of the bouquet, decorations, celebrations, garden, rituals, etc. Among different parts of a plant, the flower is the most attractive part due to its beauty and fragrance.
Let’s learn more about inflorescence and different types of inflorescence.
Types of Inflorescence
Types of Inflorescence
In a plant, flowers may grow either as a single flower or as a group. 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.
In this type of inflorescence the main axis continues to grow and does not terminate in a flower and give off flowers laterally in acropetal manner (Where old flowers are arranged lower side and young flowers are upper side).
This is of following different types :
1. Raceme - When peduncle or (main axis) is elongated and flowers are pedicellate. Eg. Radish, Mustard
When peduncle is branched and each branch bear pedicelated flowers like racemose and are arranged in acropetal manner known as compound raceme or panicle Eg. Gulmohar, Neem.
2. Spike - In it peduncle is elongated but flowers are sessile. Eg.Achyranthes.
When peduncle is branched and each branch bear spike, like infloresence then the small branch having flower is called spikelet and this arrangement is called as spike of spikelet. Eg. in the members of grass family (Gramineae) wheat
3. Catkin/Amentum - In it peduncle is thin, long and weak, and flowers are sessile and unisexual Eg. Mulberry, Betula, Oak.
4. Spadix - In it peduncle is thick, long and fleshy and have small sessile and unisexual flowers covered with one or more green or colourfull bracts.Eg.Colocasia, Maize, Aroids, Palms, Grain of maize is fruit long filamentous threads protruding at the end of a young cob of maize are styles.
5. 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 inflorescence peduncle is branched, then each branch has flower cluster, then this type of inflorescence is called compound corymb. egPyrus terminalis
6. Umbel - An inflorescence in which the flower stalks are of more or less equal in length, arise from the same point, At the base of flowers stalk, 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.
7. Capitulum/Racemose head (Anthodium) - In it the growth of peduncle is retarded and it become broad, flattened concave or convex. On it small flowers are found. These flowers are called floret.
If all the flower of capitulum are same, then it is called homogamous. If the younger flower are present towards centre and older towards the periphery, than it is known centripetal order. The flowers which are present in centre called disc floret and flowers at periphery are called as ray floret and arrangement of this type is called 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, because all flowers are pollinated at same time. Eg. Sunflower, Zinnia, Marigold.
In this type of inflorescence, the peduncle terminate in a flower. In it the older flowers are present at upper portion and young buds are arranged towards base. This arrangement is called basipetal succession.
1. Uniparous cyme/Monochasial cyme - The peduncle ending in a flower producing lateral branch at a time ending in a flower. It is two types –
(a) Helicoid cyme - When all lateral branches developed on the same side on peduncle then it is called helical cyme.
Eg. Heliotropism, Saraca.
(b) Scorpioid cyme - In this type the lateral branch develops on one side and the other branch will develop opposite to first one, i.e. they lie alternate to each other. Eg.Begonia, Vine.
2. Dichasial or biparous cyme - In this type 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. Bougainvillea, Jasmine, Teak, Mirabilis.
3. Multiparous cyme/Polychasial - In this type peduncle ends in a flower and from the base of it many lateral branches arise, which also terminated in flower, this arrangement now also occur on these lateral branches Eg. Calotropis(madar), Nerium, Asclepias,Some species of croton and Euphorbia.
Special Type of Inflorescence
1. Cyathium - The bracts or the involucre become fused to form a cup-shaped structure on the margin of it secretory glands are found. In the central part of cup-shaped structure a female flowers is found, which mature earlier. Due to the growth of pedicel this come out from the cup-shaped structure. Female flowers are surrounded by small male flowers. These are also found on Pedicel. The male flower, which lie toward centre mature earlier than the flowers which are towards periphery.
This inflorescence is found in Euphorbiaceae family like Euphorbia, Poinsettia, Pedilanthus.
2. Verticillaster- This type inflorescence is found in Labiatae/Lamiaceae family. In this type of inflorescence leaves are arranged in opposite manner on stem. From the axil of each leaf inflorescence develops. From the main axil, lateral axil arises, on which flowers are found. Now from these branches lateral branches developed also. On these branches flowers are found also. In this inflorescence each dichasial chyme changes into monochasial (scorpioid) cyme. Eg. Salvia, Ocimum, Coleus
3. 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
4. Mixed inflorescence – Sometimes flowers are arranged in both racemose and cymose manner on same peduncle called mixed inflorescence.
2 Inflorescence classification according to different parameters
Inflorescence diversity evolves by changes in a few basic parameters: (i) basic branching patterns (ii) differential elongation of the axes (branches) of different orders and (iii) repetition of branching patterns to produce “compound” (double, triple, multiple) patterns. Of the parameters listed above, the basic branching patterns primarily distinguish the different inflorescence “types” and, concomitantly, have led to most of the confusion in terminology.
2.1 Branching patterns: The two extreme forms, racemose and cymose, and their combination in the thyrse, and the developmental sequences racemose → cymose and dichasial → monochasial
Two basic contrasting branching patterns that occur in inflorescences are racemose and cymose. In the racemose pattern (Fig. 1), the main (first-order) axis (branch) has a variable (not limited) number of lateral (second-order) branches, but there are no higher-order branches. Thus, what is fixed is the number of branching orders (not more than two thus, only first order and second order) and what is variable (not limited) is the number of second-order branches. In a racemose pattern, the main (first-order) axis can be terminated by a flower (closed, determinate inflorescence) or not (open, indeterminate inflorescence). In contrast, in the cymose pattern (Fig. 1), the first-order axis (branch) never has more than two second-order axes (branches) and never more than two extrafloral leaves (phyllomes). However, the second-order branches can branch one or more times in the same way. Thus, what is fixed is the number of lateral branches of each axis (not more than two) and what is variable (not limited) is the number of branching orders. In a cymose pattern, the first-order axis is commonly terminated by a flower, but there are also cases without a flower (see below). The cut-off between two and three next-order branches for a distinction between the two major branching patterns makes sense because the occurrence of one and two next-order branches is very common, whereas three are much more rare. This is because of the common presence of one or two prophylls in branching systems, which function as pherophylls for branches of the next higher order. A cymose branching complex is called a cyme. If in a cyme all branching axes have two lateral branches, it is a dichasium, whereas if all axes have only one lateral branch, it is a monochasium (Fig. 1). A cyme can also consist of dichasial and monochasial parts, in which case branching as a rule begins dichasial and ends monochasial (Fig. 1). The definition of cyme and cymose used here was introduced by Wydler (1851) and elaborated by Troll (1957, 1964) (see also D. & U. Müller-Doblies, 1987 ). Unfortunately, in American and British texts the words “cyme” and “cymose” are often not used in this sense, but have been vaguely defined (sometimes based on the centrifugal vs. centripetal opening of flowers or the presence vs. absence of a terminal flower Rickett, 1944, 1955 ), which has caused much confusion (see above).
The two contrasting extreme branching patterns, racemose and cymose, and their combination in the thyrse. For the sake of simplicity only branches (without pherophylls and prophylls) are shown. In addition, flowers that terminate the branches are not shown in the two extreme branching patterns because the branches of the lower-most order may or may not terminate in a flower.
In both racemose and cymose patterns, the plant is flexible in the number of flowers it can produce per inflorescence. To increase flower number in the racemose pattern, the main axis becomes longer and produces more lateral flowers, whereas in a cymose pattern more branching orders are produced. Where do these two patterns occur? In an inflorescence, ramification usually starts in a racemose fashion to expand and expose flowers in the lowest-order branch and then second- or higher-order branches may become cymose (racemose → cymose). As a rule, it does not proceed the other way around. Thus, cymose ramification is secondary in development. The term “cyme” cannot be used for an entire inflorescence because the main axis of a flowering shoot regularly has more than two phyllomes it can only be used for partial inflorescences (i.e. subunits of the branching system of an inflorescence Troll, 1964 , pp. 33, 102). Such an inflorescence with racemose primary branching and cymose secondary branching is a thyrse if open (i.e. if not terminated by a flower) or a thyrsoid if closed (i.e. if terminated by a flower). The term “thyrse” was first defined by de Candolle (1827) and more strictly by L. & A. Bravais (1837) and later by Troll (1964) . For a thyrse or thyrsoid that has only one or two cymes so that its flower-bearing terminal part looks like a cyme, the term “brachium” (monobrachium or dibrachium) has been proposed ( D. & U. Müller-Doblies, 1987 ). However, a brachium often occurs together with more richly branched thyrses and thus may represent one end of a spectrum of forms in a species and so a special term is not useful (e.g. Troll & Weberling, 1989 , fig. 29, Saponaria pulvinaris). Thus, it can simply be called a thyrse with only one or two cymes. To call it a cyme, as unfortunately has sometimes been done, contradicts the definition of a cyme as having not more than two phyllomes on each axis order (see above). Another unfortunate use of terms is indeterminate for racemose and determinate for cymose (e.g. Prenner et al., 2009 ). An indeterminate axis lacks a terminal flower, whereas a determinate system has a terminal flower. However, racemes as most usefully defined can have a terminal flower (botryoids) and, conversely, cymes often lack a terminal flower on their first-order axis (e.g. in some Betulaceae and Fagaceae Abbe, 1974 Fey & Endress, 1983 ). If a branching unit has not more than one or two (lateral) flowers, a distinction between racemose and cymose cannot be made unless it can be shown to be evolutionarily derived from a more richly branched ancestor in which the pattern is clear.
Rarely, there are specialized inflorescences that are difficult to categorize in the way explained in this section. For instance, the inflorescence form of Geranium (Geraniaceae), called “geranioid” by Schroeder (1987) , can formally be seen as a multiple thyrse. However, it is somewhat special and, rather than searching for the “best fitting” general name, for a better understanding it would be more useful to compare these inflorescences primarily with those of other Geraniaceae that are less unusual.
There are several specialized terms for monochasial partial inflorescences depending on the three-dimensional pattern of ramification (e.g. scorpioid and helicoid cymes, cincinnus, bostryx, rhipidium). I will not deal with these forms here because they are subordinate to the main types. These forms have been reviewed comprehensively by Buys & Hilger (2003) .
2.2 Relative length of primary and secondary axes in racemose inflorescences
In contrast with basic branching patterns, the classification of different relative lengths of axes (branches) shows how, in a system of two branching orders, different inflorescence shapes arise by differential elongation of axes of different orders (Fig. 2). This classification focuses purely on racemose inflorescences, whereas inflorescences with racemose and cymose subunits (thyrses) are not further subdivided based on differential axis length.
Most common forms of racemose inflorescences by variation of relative length of primary and secondary axes in the region of ramification: raceme (both long) spike (primary long, secondary short) umbel (primary short, secondary long) head (both short). In all four cases, variants with and without a terminal flower of the main axis can be distinguished.
In this context, if all axes (branches) of the first and second order are elongate, the inflorescence is a raceme (a botryum if open and a botryoid if closed). If the first-order axis is elongate and the second-order axes are short, the inflorescence is a spike (a stachyum if open and a stachyoid if closed). If the first-order axis is short in the branching region and the second-order axes are elongate, the inflorescence is an umbel (a sciadium if open and a sciadioid if closed). If all axes are short in the branching region, the inflorescence is a head (a capitulum or cephalium if open and a cephalioid if closed see also D. & U. Müller-Doblies, 1987 ).
2.3 Repetition of basic (branching) patterns in racemose inflorescences and the case of the panicle
Repetition of basic branching patterns within an inflorescence is another pathway to higher-order branching (Fig. 3). If, in a racemose branching system, flowers are replaced with racemose partial inflorescences of the second order, the inflorescence is a double (or compound) raceme (diplobotryum) if open or, correspondingly, a diplobotryoid if closed a diplostachyum if open or a diplostachyoid if closed etc. Even more complex multiple compound patterns are possible, such as a triple raceme, a quadruple raceme etc. Especially complex are inflorescences of Euphorbia, in which the well-known module, the cyathium, is a thyrsoid. In turn, numerous cyathia are commonly arranged in a thyrsoid. Thus, the entire complex is a compound thyrsoid ( Müller-Doblies et al., 1975 ). Compound racemes exhibit an additional dichotomy, depending on whether all racemose partial inflorescences are lateral (homothetic compound raceme i.e. all racemes of the same axial order) or whether there is also a terminal raceme (heterothetic compound raceme i.e. racemes of different axial orders Troll, 1964 ). Typhaceae exhibit especially complex multiple compound racemose inflorescences that have been studied in great detail by Müller-Doblies (1969, 1970) .
Repetition of basic branching patterns in racemose inflorescences and the case of the panicle.
A special case is the panicle (panicula see Wydler, 1851 Čelakovský, 1893 Pilger, 1921 Troll, 1964 ). In a paniculate ramification pattern, there is neither limitation in the number of branching orders nor in the number of flowers within one branching order. Because this pattern is in no way extreme, it is more difficult to describe than the racemose or cymose patterns. Each branch terminates in a flower. Branching is often richest at (or close to) the base of the main branch, where it can encompass several branching orders. Moving up the main branch, branching becomes successively less rich (encompassing fewer branching orders) and the uppermost lateral branch may consist of a single flower. A panicle could be described as a multiple compound botryoid with continuously decreasing flower numbers on the branches of the second-order and continuously decreasing branching orders towards the apex of the inflorescence. A paniculate pattern is in some way intermediate between a cymose and a racemose pattern. It is not cymose because each branch can have more than two lateral branches of the next higher order, and it is not racemose because it has branches of more than two branching orders. It differs from a compound botryoid because, moving up the first-order branch, the second-order branches do not abruptly change from second-order botryoids to single lateral flowers. Examples of groups with panicles are in Malvaceae-Sterculioideae, Hydrangeaceae, and Oleaceae ( Troll, 1969 ).
The arrangement and distribution of flower in the axis of plant is called inflorescence. The supporting stalk in inflorescence is known as peduncle. The supporting stalk of individual flower is called pedicel.
Solitary terminal is the inflorescence in which single flower of the terminal part of growth.
Solitary axillary: If single flower develops from the axis of leaves and branches of plant, then the inflorescence will be solitary axillary.
Based on the mode of distribution and origination of flower, in plant, inflorescence can be categorized as:
In this type of inflorescene, the main axis of inflorescene does not terminate in flower but continuous to scene does not terminate in flower but continuous to grow and fives flowers laterally. The flower at lower or outer side is older and upper or inner flowers are younger. It is termed as arrangement of flowers in zeropetal or centripetal succession.It is of further following types:
In this inflorescene, the main axis is long and bears laterally flowers of equal length. E.g. mustard.
It consists of a long laterally like in racemose. E.g. Amarenthus, etc
- Catluin or Amentum:
In catluim, the flowers are arranged like that of spike but consists of more compactly arranged and unisexual flowers. The axis is long and pendulous. All the flowers of certain mature at the same time and fall as a unit. E.g. Mulberry,etc.
It is also like spike but axis is fleshly and whole axis is enclosed by one or more large bracts called spathes. E.g. banana. The upper part of it consists of flowers.
The arrangement of flowers in corymb is like in spike but the main axis is short and the pedicals of flowers are of varying length so that they are on the same level. E.g. candytuft. In some cases, the main axis is long and upper flower form corymb whereas lower form raceme. E.g. mustard.
It consists of a very short axis. All the flowers have long stalk arising from the same point e.g. Cantella.In some cases, a flower is represented by an umber and is called compound umbel. It is foung in Coriandrum.
- Head or capitulum
In this inflorescene, the main axis is compressed and forms a convex structure called receptacle. On the receptacle, sessile less flowers (florets) are arranged in a centripetal order. The whole inflorescene is surrounded by an involucre of bracts. The members of family compositae like sunflower, marigold, etc bear it.
The main axis ends in a flower and only are lateral bud grows and again ends in a flower. It is of two types:
What cymose and racemose?
in a typical raceme the main axis is elongated and bears laterally a number of flowers. each flower has a pedicel or stalk e.g,cassia fistula(amaltas).
it is a racemose infloresence in which the main axis is elongated raceme but the flowers are sessile are sessile i.e., without pedicel (stalk). eg. Achyranthus(puth kanda) and bottle brush.
it is the spike that usually bears only pistillate or staminate flower e.g. mulberry and willow.
in corymb the main axis is comparatively short and stalks of the lower flowers ere longer than upper younger ones. Therefore all the flowers lie at the same level e.g. Iberis(candytuft).
In this type of inflorescence, main axis is shortened. Flowers are stalked. Pedicels are of equal size, therefore, all the flowers seems to be arising from nearly the same level e.g. Hydrocotyl(brahmi booti), and Onion etc.
in some cases a number of umbels are persent on the tip of the main axis such a compound inflorescence is called umbel of umbel of compound umel e.g carrot.
- Secondary buds always develop on the same side of the stem: helicoid cyme or bostryx