Plants and People

Flowers

Why a Flower?

The Reproductive Structure of Flowering Plants:

PerianthPetal: CorollaSepal:Calyx

Flower Anatomy

Calyx: the outer whorl of sepals; typically these are green, but are petal-like in some species.

Flower Anatomy

Corolla: the whorl of petals, which are usually thin, soft and colored to attract animals that help the process of pollination.

The coloration may extend into the ultraviolet, which is visible to the compound eyes of insects, but not to the eyes of birds.

Flower Anatomy

Androecium (from Greek andros oikia: man's house): one or more stamens, each with a filament topped by an anther where pollen is produced.

Pollen contains the male gametes.

Flower AnatomyGynoecium (from Greek gynaikos oikia: woman's house): all the female parts—the pistil(s) with ovule(s) inside.

Flower AnatomyThe basic unit of the female reproductive structure is the carpel. Each physcial body is called a pistil.

A flower may have a single carpel, which is a simple pistil (unicarpellate), or several carpels united in one compound pistil (syncarpous), or a cluster of un-united carpels/pistils (apocarpous)

The sticky tip of the pistil, the stigma, is the receptor of pollen.

The supportive stalk, the style, becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, containing the gametes, housed inside the ovary.

Flower Anatomycarpel

fertilization carpel structure

Evolution of the Carpel

See figures 3.1 and 3.2 in your book

Fruit and Seed FormationA fruit develops from an ovary. A seed develops from an ovule.

Flower Structure Variation

imperfect

perfect

imperfect

Flower Structure VariationOvary Position

A. ovary superior, floral parts hypogynous

B. ovary inferior, floral parts epigynous

C. ovary half-inferior

D. ovary superior, floral parts perigynous, hypanthium cup shaped

Flower Structure Variation

A flower having sepals, petals, stamens, and pistils is complete; if a flower is lacking one or more of these whorls, it is said to be incomplete.

no stamens present = incomplete

incomplete

complete

Inflorescences

An inflorescence is a group or cluster of flowers. It may be branched or unbranched. Modifications can involve the length, variations in the proportions, compressions, and swellings, and the order in which the flowers open.

Usually the modifications have been evolved to optimize the plant’s method of pollen dispersal.

Inflorescences

raceme

umbelcorymb

spike

Inflorescences

catkin

spadix head

Pollen Dispersal by AnimalsBees, Beetles, Bats, Birds, Butterflies, etc…

Symmetry

Flowers that are actinomorphic have "radial symmetry", meaning they can be divided into symmetrical halves by more than one longitudinal plane passing through the axis, much as a pie can be cut into several equal and identical pieces.

Zygomorphic flowers are "yoke shaped” or have"bilateral” symmetry, where flowers can be divided by only a single plane into two mirror-image halves, much like a yoke or a person's face.

Dicot versus Monocot

Dicot Monocot

Lab Objectives1. Flowers are arranged in groups called inflorescences. We will examine some

inflorescences particular to certain families later in the semester. For now, know what an inflorescence is and which ones we looked at today.

2. DRAW a longitudinal section of a typical flower labeling the following parts: receptacle, calyx, sepals, corolla, petals, perianth, pedicel, ovary, ovule, style, stigma, pistil, gynoecium, anther, filament, stamen, and androecium.

3. EXAMINE by dissection the floral material provided making long and cross sections of the flower and its parts. On a separate sheet of paper, SKETCH the flowers and label the parts. Then, FOR EACH FLOWER, answer the following questions:

A. Is the flower actinomorphic (regular) or zygomorphic (irregular)? B. How many sepals are present? Petals? Stamens? Carpels? To count carpels, count

the locules, styles, style branches, and/or the zones of placentation by cross- sectioning the ovary.

C. Is the ovary inferior or superior? D. Is the flower from a monocotyledonous or dicotyledonous plant? E. Is the flower perfect (both sexes present) or imperfect? Complete (all four floral

whorls) or incomplete?