Examine the materials in the lab, becoming familiar with modes of pollination, the factors that are directly involved in the interaction between plants and animal pollinators, and the ramifications of pollination on the reproduction of flowering plants.

The basic structure of a flower is depicted in the drawing above. There are four series of floral parts, usually arranged in whorls, each with its own set of functions. Evolutionary botanists regard a flower as a highly modified stem axis around which are arranged a series of modified leaves. In some floral parts it is easy to visualize their leaf-like nature, but in others it takes some extra study to understand the origin of these organs from leaf-like ancestors.

The sepals (collectively the calyx) is the lowermost whorl (painted green). In real life, too, they are most commonly green and leaf-like, and function to protect the entire flower in the bud as its other parts are developing. As the flower opens the calyx often folds out of the way.

The petals (collectively the corolla) constitute the second whorl of parts of a flower (painted red). Their primary function is to attract animal pollinators via a visual signal, such as color, pattern, and shape. Neither the calyx nor corolla are involved directly in production of gametes; however, their roles are critical to the success of the reproductive process in flowering plants.

The stamens constitute the third whorl of floral parts. Each generally consists of a stalk-like filament tipped by an anther. The anthers (painted yellow)areis the structures in which the pollen grains are produced.

The female part of the flower (the pistil) consist of three parts: The ovary (painted blue), the chamber that contains the ovules/seeds; the style, the tissue through which the pollen tube cell grows to the vicinity of the ovules; and the stigma, the receptive tissue that recognizes legitimate pollen and promotes the germination of the pollen grain.

Examine the selection of fruits on display and determine the carpel number for each species. Are the carpels here free or fused together?

With over 250,000 species of flowering plants, you wouldn’t expect each one to have identical flowers. Indeed, there are numerous variations on the general theme described above, yet it is still amazing that all flowers can be viewed as a modification of this typical pattern.

To see examples of these features, click on the links:

(1) Number of parts

The number of parts of each organ series can vary considerably among species, but rarely varies within a species. Given this information, and referring back to the lab on Classification, how would you rate the general value of numbers of flower parts as a taxonomic character? Note that the numbers of parts in different series vary independently from each other. That is, just because a calyx in a species has a certain number of parts doesn’t mean that the number of petals will be the same. Examples:

numerous perianth parts (i.e., of an undetermined number) - Illicium
5-merous corolla - Ipomoea; Polemonium
4-merous corolla - Ixora;
3-merous perianth - Tricirta

(2) Fusion of parts

Fusion of parts is a common source of floral variation. Like parts may be fused (e.g., sepals fused to sepals, carpels fused to carpels), and unlike parts can be fused (e.g., stamens can be fused to the corolla). Furthermore, the extent to which parts are fused to each other can also vary considerably. Note that the fusion of parts can alter the shape of the flower.

(3) Loss of series

Another “option” for floral variation is the complete loss of one or more series of floral organs. For example, as you’ll see below, many flowers lack a corolla of any kind. Evolutionary biologists regard the lack of a series as the evolutionary loss of this series.

(4) Sexuality

A special variation on the pattern described in “C” above is the lack of one or the other gamete-producing series. This produces unisexual flowers, and has profound implications on the reproductive biology of species possessing this pattern

Stated simply, pollination in flowering plants is the process beginning with the departure of pollen from the anther and ending with its deposition on a stigma. Note that pollination is not the same as fertilization. Pollination must occur prior to fertilization. In non-flowering seed plants, pollination involves deposition of pollen at or near the micropyle of an ovule.

Movement of pollen from one plant/flower to another requires some agent - generally wind or an animal (although water can also be included). When a non-animal vector is responsible for pollen movement, pollination is termed Abiotic. When an animal is the agent of movement, pollination is termed Biotic.