BOTANY LABORATORY PRACTICALS (PLANT ANATOMY AND MORPHOLOGY) - O.A. SHEVCHUK - 2014

THE FLOWER

TOPIC 8. STRUCTURE AND CLASSIFICATION OF INFLORESCENCES

General Remarks. Only a few plants bear solitary flowers (such as poppy, magnolia, tulip, etc.); more commonly, flowers are grouped along a common axis to form an inflorescence.

An inflorescence is a cluster of flowers arranged on a floral axis (peduncle) in a specific pattern. Based on their branching patterns, infflorescences are divided into two major groups: indeterminate (or monopodial) and determinate (or sympodial).

Monopodial inflorescences are characterized by an indeterminate (unlimited) growth of the main axis. They can be simple, when flowers are borne singly on the axis in the axils of bracts or on pedicels, and compound, when the lateral axes of the first order bear simple inflorescences. Types of simple indeterminate inflorescences include: raceme - an inflorescence in which flowers with pedicels of nearly equal length are arranged alternately along the main axis (bird cherry, lily of the valley); spike - an inflorescence bearing sessile flowers along the main axis (plantain, sedge, birch); spadix - an inflorescence with a thickened, fleshy axis bearing sessile flowers (female inflorescence of maize); corymb - an inflorescence in which flowers with pedicels of varying lengths are arranged along the main axis such that all flowers lie in roughly the same horizontal plane (pear, apple). Umbel has a greatly shortened axis where flowers with pedicels of almost equal length radiate from a single point (primrose, onion). HEAD (capitulum) is an inflorescence with a shortened and somewhat expanded axis bearing sessile or short-pedicelled flowers (beech, clover). Head/basket - an inflorescence with a flattened, disk-like expanded axis bearing sessile flowers surrounded by an involucre of one or more rows of bracts (dandelion, sunflower).

Types of compound indeterminate inflorescences: compound spike - an inflorescence where simple spikes are arranged along the main axis (rye, wheat); panicle - an inflorescence where the main axis bears simple racemes or corymbs (lilac, oat); compound umbel features lateral axes that terminate in simple umbels (carrot, dill).

Determinate inflorescences exhibit a different branching pattern - sympodial: in a dichasium, the lateral axes are opposite; in a pleiochasium, they are whorled; and in a cincinnus and bostryx, they are spiral.

Inflorescences make small flowers much more conspicuous to insect pollinators, while in anemophilous (wind-pollinated) plants, they enhance the capture of wind-borne pollen. The evolutionary development of various inflorescence types should be viewed as an adaptation for cross-pollination.

Objective: to familiarize oneself with MODERN CONCEPTS OF inflorescences, their origin, and biological significance; to study the Classification and Structure of inflorescences, and to learn how to identify inflorescence types.

Materials and equipment: live and preserved material, as well as herbarium specimens of species from the following families: Plantaginaceae, Salicaceae, Rosaceae, Papilionaceae, Compositae, Gramineae, Primulaceae, Euphorbiaceae, hand lenses, dissecting needles, charts.

Tasks

1. Examine and study the set of herbarium specimens representing simple monopodial inflorescences.

2. Examine and study the set of herbarium specimens of compound monopodial inflorescences, and determine the type and name of each inflorescence.

3. Study the set of herbarium specimens with determinate inflorescences.

Label the drawings and draw Conclusions.

Conclusion

Self-Assessment Questions

1. What is an inflorescence?

2. Do all plants form inflorescences? What are the advantages of plants with inflorescences over those with solitary flowers?

3. What is the difference between simple and compound inflorescences?

4. How can a sympodial inflorescence be distinguished from a monopodial one?

5. Into what two groups can simple inflorescences be divided?

6. What are the Characteristic Features of each type of simple and compound inflorescence?

7. What are the inflorescences called in which flowers with pedicels of varying lengths are arranged along the main axis?

8. What is the inflorescence called that has sessile flowers arranged along an elongated main axis?

9. Name all the types of determinate inflorescences.

10. To which type do inflorescences characterized by indeterminate growth of the main axis belong?

11. What is the inflorescence called that features a disc-like expanded axis and sessile flowers?