Plants and People Flowers

Why a Flower?

The Reproductive Structure of Flowering Plants: Perianth Petal: Corolla Sepal: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 Anatomy

Gynoecium

(from Greek

gynaikos oikia

: woman's house): all the female parts—the

pistil(s) with ovule(s) inside

.

Flower Anatomy

The 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 Anatomy carpel

fertilization carpel structure

Evolution of the Carpel

See figures 3.1 and 3.2 in your book

Fruit and Seed Formation

A fruit develops from an

ovary

. A seed develops from an

ovule

.

Flower Structure Variation

imperfect perfect imperfect

Flower Structure Variation

Ovary 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.

raceme

Inflorescences

spike corymb umbel

spadix

Inflorescences

head catkin

Pollen Dispersal by Animals

Bees, 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 Objectives

1. 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?