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علوم گیاهی - Inflorescence

Inflorescence

پنجشنبه 8 تیر 1391 04:37 ب.ظ

نویسنده : عسکر اله قلی

 Inflorescences

The sum of all flowers of a plant is called inflorescence. Inflorescences exist in many different forms and shapes, so in this week's “Article of the Weel” I want to show the basic and common variants of inflorescences. I'll not show all of them, but only the main types.

So first, let us check out some basic terms. When you look at an inflorescence, you have maybe noticed, that some of them are ending into a terminal flower and others not. In Botany we speak of a monotelic(closed) inflorescence in first case and of a polytelic (opened) inflorescence in the second

It's also makes a different, if an inflorescence only consists of single flowers or in turn are compounded of small inflorescences by itself. First we look at inflorescences, which consist only of single flowers.

I. simple Inflorescences

a) ear: the ear is possible the most simple type of an inflorescence. Here, the flowers are sitting directly into the axil of their bracts. Ears can be found at some species of the Poaceae (e. g. the Genus ofHordeum), but also at the Genus Plantago. A cone is also a variant of an ear.

b) raceme: the raceme is not very different from the ear. The only difference is, that the flowers of a raceme are sitting at the end of a short stalk, growing from the axil of a bract. This type of inflorescence can be found e. g. at the Genus of Viccia.

c) umbel: At the umbel, the flowers also are sitting on a stalk. All stalks starts at the same point of the shoot axis. The bracts of the flowers often forms a such called involucrum. So the whole inflorescence looks like a umbrella. Umbels are the typical character for the Apiaceae family, which is also calledUmbeliferaceae. Be careful, because sometimes, a raceme is formed like an umbrella (e. g. at Capsella bursa-pastoris L.), but this are no real umbels, because here the stalks are not starting at the same point.

Sometimes, an umbel consists of smaller umbels. This is a double-umbel (d)

e) & f): catkin: a catkin in basically no more than an inverted and hanging ear or raceme. This type of inflorescence is typical for many genera of our native trees like Alnus, Populus or Salix.

note: in this picture the small bracts of 
the spadix and the head 1 has not be draw

g) spadix: A spadix is a special type of an ear, but here, the floral axis is thickened and cylindrical. Spadices can be found e.g. at Zea mays L. (corn) and the most species from the Araceae. They are also typical for the Genus Typha (bullrush or corndog grass) of the Typhaceae.

e) head 1: The first type of the head-formed inflorescence is similar to the spadix. The transition is fluently indeed. The flora axis is also thickened but more jolted. This inflorescence is typical for the TrifoliumGenus (e. g. Trifolium medium ssp. medium L. in this Blog)

f) head 2: The second head inflorescence is the characteristic inflorescence of the Asteraceae family (with species like common daisy, common dandelion or the sun flower). Here the floral axis is compressed even more than the first head type. The flowers are sitting directly at this floral axis and their bracts are forming a involucrum.

II. compounded inflorescences

O.k. Folks, now it becomes complicated. In the previous inflorescences we always have a single flower per bract. But sometimes, a inflorescence is multi-branched, that means instead of a flower it has smaller floral axis, growing out from the axial of the bracts.

In this case it depends on how the inflorescence is branched. First, we have two basic types again: the panicle and the cyme.


a) panicle: At a panicle, a new floral axis grows from a single bract. This axis can be branched by itself. The branching doesn't follow a strict scheme and flowers can grow everywhere. A panicle is always monotelic.

b) cyme: If the successive branches follows a scheme, we speak of a cyme. If there is only one new axis per branching, we call it a monochasium. With two new axis per branching, we called dichasium.

Now we subdivide the monochasial and dichasial cymes into three types again.



c) thyrse: A thyrse is simply a inflorescence with dichasial cymes as branches. The inflorescence of Aesculus hippocastanum L. (conker tree) is a good example for a thyrse

d) depranium: A depranium is a monochasial cyme. Here, the floral axis are helical applied towards the main axis.

e) rhipidium: The rhipidium is basically the opposite of the depranium. The successive floral axis grow in a zigzag pattern. The inflorescence of the tomato is e. g. a rhipidium


An inflorescence may be defined as a cluster of flowers,
all flowers arising from the main stem axis or peduncle:


1. Cyme


2. Umbel


3. Inflorescence Types



4. Catkin: Inflorescence With Unisexual Flowers

Left: Male (staminate) catkin from the white mulberry (Morus alba), a fruitless variety commonly planted as a shade tree in southern California. Right: An individual male flower containing four stamens, each with an anther and a filament. At the base of each filament is a fleshy green sepal. Male trees are known as "fruitless mulberry" because they do not produce messy fruits that stain clothing and walkways. Since mulberries are wind-pollinated, male trees produce copious pollen which can raise havoc with hay-fever sufferers.

Female catkin from a variety of black mulberry (Morus nigra). Mulberry flowers are produced in a catkin, with male and female catkins on different trees. Male flowers have four stamens while female flowers consist of single pistil tightly enveloped by four inconspicuous sepals. Each carpel or pistil (also referred as a gynoecium) consists of a forked stigma, a short style and a spherical ovary. Each ovary (carpel) becomes a drupelet and the ripened cluster of drupelets (syncarp) is called a multiple fruit. In the aggregate fruit of a blackberry, all the drupelets of the cluster (syncarp) come from a single flower. Seedless, parthenocarpic fruits may be produced without pollination by male trees.


5. Spadix: Inflorescence Of The Arum Family (Araceae)

The spadix is the characteristic inflorescence of the remarkable arum family (Araceae). It consists of a thickened, fleshy axis (spike) bearing clusters of sessile, apetalous, unisexual flowers. The small unisexual flowers are packed together along the lower region of an erect, phallus-like central spike, typically with male flowers above the female. The upper region of the spadix is usually devoid of flowers. Male (staminate) flowers consist of numerous stamens packed together, while female (pistillate) flowers consist of numerous individual pistils. Individual flowers are reduced to a single stamen or pistil (gynoecium). The spadix emerges from a vase-shaped or funnel-like modified leaf or spathe which is often brightly colored. The spadix of some arums emits a putrid odor that attracts carrion flies for pollination.

The spadix of some aroids produces a remarkable amount of heat during cold weather. In fact, the temperature of the spadix can be up to 30 degrees Celsius above a cool air temperature of 10 degrees Celsius. This may stimulate the activity of pollinator insect visitors and help to vaporize the stench of the flowers. The heat mechanism may involve male flowers packed around the spadix. In some species in which the upper part of the spadix is sterile (flowerless), the heat mechanism appears to be in the cells of this sterile tissue. Like heat-producing tissue in mammals, the cells in these flowers rapidly oxidize lipids and carbohydrates, thus releasing heat. Heat production in aroids is discussed in a fascinating article by R.S. Seymour in Scientific American, March 1997.

The bizarre Malaysian Amorphophallus paeoniifolius. An enlarged, inflated, flower-bearing spadix protrudes from the vase-shaped spathe. Clusters of yellow male flowers (stamens) can be seen above the whitish stigmas of female flowers (pistils).


Inflorescence Definitions

Note: Inflorescences with youngest flower at the end of the main axis (rachis) are called "indeterminate" (i.e. terminal bud continues to produce new flowers). Inflorescences with oldest flower at the end of the main axis are called "determinate" (i.e. terminal bud stops growing and lateral flowers are produced from axillary buds.)

  • Solitary: A single flower on a caulescent or acaulescent stem.

  • Spike: Unbranched inflorescence with sessile flowers (no pedicels).

  • Raceme: Unbranched inflorescence with flowers on pedicels.

  • Panicle: A branched or compound raceme (i.e. main rachis with branches bearing flowers on pedicels).

  • Corymb: Flat-topped inflorescence with youngest flowers at the end of main axis or rachis.

  • Cyme: Flat-topped inflorescence with oldest flowers at the end of main axis. [Includes simple, compound and scorpioid cymes.]

  • Umbel: Flat-topped inflorescence with all the pedicels arising from a common point. [Includes simple and compound umbels.]

  • Catkin or Ament: A spike-like inflorescence of unisexual, apetalous flowers, often pendent and falling as a unit. This is the typical inflorescence of willow (Salix), cottonwood (Populus), oak (Quercus), alder (Alnus) and birch (Betula). All these species belong to a polyphyletic group of angiosperm families known as the Amentiferae.

  • Spadix: A thick, fleshy spike of unisexual, apetalous flowers, often surrounded by a vase-shaped or funnel-like modified leaf or spathe which is often brightly colored. The male flowers are typically clustered above the female flowers on an erect, phallus-like spike. This is the characteristic inflorescence of the arum family (Araceae).

  • Spathe: A leaf-like bract or sheath that envelops an inflorescence. In the arum family (Araceae), the vase-shaped or funnel-like spathe is often brightly colored. The most remarkable spathe surrounds the inflorescence (spadix) of the corpse flower (Amorphophallus titanum), so named because of the stench of the blossom. Native to equatorial tropical rain forests of Sumatra, Indonesia, this amazing plant attracts flies for pollination. At its maximum development, the spadix may be 8 feet tall (2.4 m) with a huge vase-shaped, pleated spathe over 4 feet (1.2 m) tall and 12 feet (4 m) in circumference. The deciduous spathe of palm inflorescences may be several feet long and quite woody. In fact, the fallen spathes of coconut palms (Cocos nucifera) are boiled, dried and waxed to produce a beautiful boat-shaped bowl.

Spathe bowls from the coconut palm (Coco nucifera). Fallen spathes are boiled, dried and waxed to produce these sleek, shiny black bowls



Inflorescence Types




Spike an elongate, unbranched, indeterminate inflorescence with sessile flowers.
Spikelet a small spike, characteristic of grasses and sedges.
Raceme an elongate, unbranched, indeterminate inflorescence with pedicelled flowers.
Panicle a branched raceme.
Corymb a flat-topped raceme with elongate pedicels reaching the same level.
Compound Corymb a branched corymb.
Umbel a flat-topped or rounded inflorescence with the pedicels originating from a common point. Umbels can be determinate or indeterminate.
Compound Umbel a branched umbel, with primary rays arising from a common point, and secondary umbels arising from the tip of the primary rays.
Capitulum
(or head)
a dense vertically compressed inflorescence with sessile flowers on a receptacle and subtended by an involucre of phyllaries, characteristic of the Asteraceae. Heads can be determinate or indeterminate.
Thyrse a many-flowered inflorescence with an indeterminate central axis and many opposite, lateral dichasia; a mixed inflorescence, with determinate and indeterminate shoots



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آخرین ویرایش: شنبه 10 تیر 1391 06:40 ب.ظ