Inflorescence Terminology (Part 1)

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Botany 115 Terminology

Inflorescence Terminology Part 1

Inflorescence Terminology Part 2
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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.

Flowers & Multiple Fruits Of The Mulberry Family

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).

Putrid Arums That Attract Flies
The Flynapping Arum Of Sardinia
Largest & Most Foul-Smelling Arums

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.

See Spathe Bracts Of The Chilean Wine Palm

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