inflorescence

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With inflorescence or inflorescence a branched part of the will shoot axis system called, the flowers on seed plants contributes and is more or from the vegetative part of the plant less clearly defined. Characteristic for this part of the shoot are the type and extent of the branching of the shoot axis , their foliation as well as modifications in the form of elongations, compressions, thickenings, adhesions or reductions of the main and minor axes. Thus, the inflorescence represents an essential part of the habitus of the flowering plant and thus an excellent characteristic for determining the species within a family. Many inflorescences act like a large flower to pollinators , so they are better attracted than with individual flowers. This advantage is especially true if the flowers are small and individually too inconspicuous.

General

For all types of inflorescences , a number of cross-type characteristics can also be found, which appear in almost any combination with one another. They also supplement the naming of the inflorescences and have no influence on the typification.

Foliage

The distinction between the inflorescence as a generative and the vegetative part of the plant is often made on the basis of the different types of foliage:

  • Absence of the sheets in the region of the inflorescence in whole or in part and they are as high leaves formed (bracts) and thus differ from the other arrangement of the leaves, one speaks of an arrangement of the leaves or brakteosen brakteosen inflorescence.
  • In leafy bracts often speaks of a flowering shoot instead of an inflorescence. Since these leaves, despite their foliage -like appearance, also have bract-like characteristics, frondose inflorescence is the more appropriate name.
  • There is also a connecting intermediate form, the frondo-bractose inflorescence.
  • In the inflorescence area, like many woody plants, but also leaves without any bract characteristics can occur. These are small foliage leaves that are derived from the regular foliage leaves through an even series of reduction. One speaks here of frondulosic foliage, the transition to frondose inflorescence is the frondo-frondulosic inflorescence.

  • Reduced brakteose foliage

  • Complete brakteose foliage

  • Frondo bractose foliage

  • Frondose foliage

The outdated, strict division into inflorescence (brakteos) and blooming shoot (frondos) with the different bracts has given way to a classification in which the different forms of inflorescences are defined in a meaningful broader classification with the various leaves as a connecting element. A flowering shoot should therefore always be referred to as a frondose inflorescence.

Terminal bloom

There are two possibilities for the formation of the vegetation tip, namely, whether a terminal bloom forms or not. The presence or absence of a terminal flower in flowering plants is characteristic of entire families.

Closed inflorescence

If the tip of the shoot forms a terminal flower and is consumed as a result, one speaks of a closed or determined inflorescence. The individual petals exactly follow the sequence of the previous leaves ( phyllotaxis ). The terminal flower usually blooms first (precursive unfolding), while the efflorescence of the side flowers is usually promoted from the base to the apex upwards ( acropetal ), often also from the apex downwards ( basipetal ), more rarely to both Sides (divergent). Due to a lack of growth stimuli or as a form of hunger, the inflorescence can only develop in a reduced manner and be completely limited to the terminal bloom.

  • Closed inflorescence with acropetal effloration

  • Closed inflorescence with basipetal effloration

  • Closed inflorescence with divergent effloration

Open inflorescence

If the tip of the shoot continues to form bracts with buds in their axils instead of a flower and ends blindly in a mostly tapered, rudimentary end, then there is an open inflorescence. The established flower buds either all bloom or they lie upwards in ever further reduction up to the undetermined shoot apex, which may even be able to continue to grow (proliferation). The tendency, which is common in plants, that a missing terminal tip is replaced by the closest one (peaking) can also be seen here: the flower below the rudimentary tip of the shoot stands up and appears to become the new terminal flower. If its lateral origin can still be recognized, preferably through a rudiment that is still visible, it is called a subterminal flower, the lateral origin can no longer even be evidenced in terms of evolution, but only in comparison with related species, it is called a pseudoterminal flower.

  • Open inflorescence with complete acropetal effloration

  • Open inflorescence with acropetal effloration with flower buds

  • Open inflorescence with subterminal flower and rudimentary shoot apex

Approach of the branches

Although the type of branching is an elementary distinguishing feature for the various inflorescences, the attachment of the minor axis and its supporting sheet to the inflorescence axis are not relevant for the typification of the inflorescence. The different approaches depend on the position of the leaves .

  • Disperse branching

  • Decussed branch

Metatopy

The side axis carrying the inflorescence or a single flower is always in the axilla of a bract . However, a metatopia (displacement) can also occur, two cases are possible:

  • In concealment, the side axis is partly fused with its axis of descent. This means that the flowers sit much higher on the stem than the associated bracts.
  • In the recalculation, the side axis is partially fused with the stem of the support sheet. The flowers are shifted towards the leaf.

  • Flower and bract

  • Concealment

  • Recaulescence

Classic division

In the classic typology of inflorescences, the type of branching is used to distinguish the main groups . Within this, the type is determined based on the branching of the axes and, above all, their modification.

Simple inflorescences (botryen)

In the simple inflorescence, the branching type is a monopodium , i.e. a main axis with branching minor axes of the first degree (unbranched). Traditionally, this type of branching in inflorescences is called racemous and not monopodial. The basic type is the grape (botry), the other inflorescences can all be derived from it by stretching, compressing, thickening or reducing different parts of the axis. Accordingly, there are often transitional forms that mediate between the clearly developed forms. Inflorescences of this type, together with the truss types, are generally among the best known by name.

Compound inflorescences

In the case of a compound inflorescence (complex inflorescence), a simple inflorescence represents the base. However, its flowers are each replaced by a partial inflorescence (partial inflorescence). This can be racemous or zymically branched. Then it is divided into two groups.

Partial racemic inflorescences

Double botrya

If the flower is replaced by partial inflorescences of the same basic structure, a corresponding double botryum (dibotryum) is obtained. For example, a double grape is a grape whose flowers have been replaced by one grape each. If this only happens to the lateral flowers, the homeothetical form is obtained; if the main axis also forms a cluster, the heterothetical form is obtained. The flowers of the partial inflorescences can in turn be replaced by further partial inflorescences, resulting in a new level of branching. However, this always only happens with the underlying structure. Depending on the number of repetitions, one speaks of the dibotryum and tribotryum, later only generally of the pleiobotryum.

Panicle and relatives

In the panicle, the entire inflorescence and the partial inflorescence are always closed with a terminal flower . The partial inflorescences are increasingly stronger and irregularly branched towards the bottom. The side branches are called monads (one flower), diads (two flowers) or triads (three flowers) according to their number of flowers; if they are strongly branched like an independent panicle, they are called special panicles. Overall, this results in a cone shape. With a corresponding stretching of the side branches, this appearance gives way to a flat or slightly arched shape, the umbrella panicle, and with greater overstretching a funnel-shaped appearance in the case of the spirals. If a panicle is depleted of branches, it looks like a grape, only a possibly remaining branched branch and, above all, the terminal flower that is always present make it clear that it is a panicle without a doubt. Because of the similarity to the grape (botrys) one speaks of botryoid (in the case of spike-like form, stachyoid). With the loss of the terminal bloom, the path to reduction to grapes is finally complete.

Zymous partial inflorescences

In the zymous partial inflorescence, or cymes for short, the branching type is a sympodium . The main axis ends with a flower, the secondary axes branching off from the pre-leaves often peak over the terminal flower, branch out further and then also end with a flower. Depending on the number and type of branches that arise from an axis, the various partial inflorescences are distinguished:

The types with two bracts occur in the dicotyledonous , rarely in the monocotyledonous , a previous sheet the other way round in the monocotyledonous and rarely in the dicotyledonous.

Since the structures cannot be clearly distinguished from one another in the side view, the schematic structure is also shown from above.

Thyrsus

If several cymes form the inflorescence on a racemous main axis, one speaks of a thyrsus. The main axis is of the type a grape, ear or head-like compressed. Terminal flowers are not always present.

  • Thyrsus with dichasium cymes

  • Thyrsus with winding cymes

  • Thyrsus with double-wound cymes

If the zymous partial inflorescences are in turn replaced by thyrses, analogous to the special panicles of special thyrses, one obtains, as with the double botryses, double thyrses or pleiothyrses. Similarly, a distinction is made here between homeocladic and heterocladic forms, simple thyrses are always homeocladic.

  • Homeocladic thyrs with apical reduction

  • Heterocladic thyrs

  • Disjoint heterocladic thyrs

  • Pleiothyrse

Cymoid

Even if the partial inflorescences are zymically branched, the underlying structure is always racemous. So there are no zymous inflorescences. By appropriately reducing the structure, however, the entire inflorescence can appear purely zymose. One then speaks of a cymoid. Starting from the closed thyrsus forms, all cymes except for the terminal ones are not formed. Depending on the number of remaining cymes, there are monochasial, dichasial or pleoichasial cymoids. The impoverishment of cymes is intensified by acrotonic promotion. If the axes of the pleiochasium, which already shows an umbel-like character, are completely reduced, with the exception of the flower stalks, the result is a cerebral umbel that can only be recognized as such by the terminal flower that blooms first.

  • Dichasial cymoid

  • Double coiled cymoid

  • Double screw cymoid

  • Coiled or fuzzy cymoid

  • Helical or sickle-shaped cymoid

Curiosities

literature

  • Wilhelm Troll : The inflorescences; First volume. Gustav Fischer, Stuttgart 1964.
  • Wilhelm Troll: The inflorescences; Second volume, first part. Gustav Fischer, Stuttgart 1969.
  • Wilhelm Troll: Practical introduction to plant morphology. Gustav Fischer, Jena 1957.
  • Bernhard Kausmann: Plant Anatomy . Gustav Fischer, Jena 1963.
  • Focko Weberling: Morphology of the flowers and the inflorescences (= phytology. Classical and modern botany in individual representations ). Eugen Ulmer, Stuttgart 1981, ISBN 3-8001-3426-8 .
  • Peter Leins, Claudia Erbar: Blossom and Fruit. Morphology, evolutionary history, phylogeny, function and ecology . 2nd, completely revised edition. Schweizerbart, Stuttgart 2008, ISBN 978-3-510-66046-9 .

Web links

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