Land Plants – The Angiospermswww.onacd.ca

Characteristics of Angiosperms

• Are the most widespread land plants

• Comprised of 250,000 to 400,000 known species

• Are vascular plants with more specialized xylem and phloem

• Produce reproductive structures known as flowers

• Have a reduced male gametophyte (3 cells) and a reduced female gametophyte (7 cells) which decreases the time needed in which to reproduce

Flowers• Reproductive organ of the angiosperm• Designed to attract insects and other pollen bearing animals to

aid in the best pollen transfer and dispersal

•Pistil

Stamen• Stamen

• i. Composed of a filament and anther with two pollen sacs.

• ii. In pollen sacs, microspores become pollen grains.

• iii. Stamens usually grouped around pistil.

Pistil• i. Usually in center of flower.

• ii. Stigma is enlarged sticky knob to collect pollen.

• iii. Style is slender stalk.

Flowers• Ensure fertilization of the ovule

and possible development of fruit containing seeds

• Arise most commonly from the shoot or the axil of a leaf

• Most flowers are hermaphroditic but often are structured in a way that prevents self fertilization

• Have sepals and petals- sepals are usually green and leaf-like and protect the bud of the flower as it grows

- petals are often colored and delicate structures that attract pollinators by color, scent and nectar

An orchid…..Note: We usually use a lily to show the anatomy of a flower as it is a complete flower.

In different flowers the structures will vary in their appearance or may not be visible at all.

An iris…..Try to

label the parts of this iris on your own!

•Pistil = Carpel

Why Flower?• . Unlike gymnosperms, flowers attract

pollinators to carry pollen from flower to flower.

• c. Flowers and pollinator have co-evolved; for example: blue, yellow, and ultraviolet colors are within range of bee sight and pattern may lead bee to nectar at flower base.

• d. While bee collects nectar and pollen for food, pollen is also inadvertently carried to next flower.

Imperfect Flowers• An imperfect flower is a flower that has

only male parts or female parts.

• A perfect flower has both male and female parts on the flower.

Incomplete Flowers

Incomplete flowers are missing one or more of the

four main parts of a flower:

sepals, petals, stamens or pistil

Reproductive structures of flowersMALE PARTS

– Comprised of one or two whorls of stamens• Stamen is the filament topped by an anther

• The structure of the stamen often allows for specialized pollination and prevents self fertilization

• Produce microspores in the stamens which undergo meiosis to produce pollen which covers the anthers

FEMALE PARTS– Comprised of one or more pistils

• Pistil is made up of the stigma (sticky tip), style (stalk through which the pollen tube grows) and the ovary

• Produce megaspores in the ovule which undergo meiosis to produce the egg cell

Lily pollen

Microscopic anther with pollen grains

Ovule

Flower parts

Ovule inside a flower Stigma Pollen on anther Stigma, Style, 6 stamens

Cactus flower pollen

Angiosperm Life Cycle : The LilyNOTES

Double Fertilization occurs in angiosperms: each pollen

grain contains two sperm. One sperm (N) fertilizes the egg (N) and goes on to form the zygote (2N). The other sperm fertilizes the 2 polar nuclei (2N) in the embryo sac and goes on to

produce the endosperm (3N)

Endosperm is the highly nutritive tissue that provides

food for the embryo, cotyledons and young seeding

*Remember that seeds often are enclosed by fruit in angiosperms

Double Fertilization• Forming the endosperm (3N)

Seed Anatomy

Monocotyledons “Monocots”MONOCOT

Examples Grasses, grains, lilies, daffodils, tulips

Cotyledon # One, single

Leaf veins are Parallel

Vascular tissue (xylem and phloem) arranged in

Bundles

Roots are Fibrous (adventitious)

Flower parts occur in

Multiples of 3, (trimerous)

Secondary growth?

Rare

Approximately 23% of all Angiosperms are

Monocotyledons

Dicotyledons “Dicots”DICOT

Examples Maple, Oak, Elm, Sunflowers, Roses

Cotyledon # 2, double

Leaf veins are Networked

Vascular tissue (xylem and phloem) arranged in

Rings (forms annual rings in stems viewed in cross section of a stem/trunk)

Roots are Taproots

Flower parts occur in

Groups of 4 or 5

Secondary growth?

Frequent

Approximately 75% of all

Angiosperms are Dicotyledons

Dicot Seedling

Fruit• i. Include: milkweed pods, peas and

beans, tomatoes, oranges, watermelon, etc.

• ii. Function to disperse seeds using wind, gravity, water, and animals to area suitable for germination.

Why are angiosperms more successful than gymnosperms in a land environment?

• Angiosperm seeds are better protected• Herbaceous, soft tissues are able to

survive 1 to a few years• Angiosperms can go from seed to seed in

less than one year as opposed to the years this may take in gymnosperms

• The xylem cells in angiosperms are more efficient than in gymnosperms

• Pollination is more successful as angiosperms are not simply reliant upon the wind. This increases the occurrence of cross fertilization which in turn increases genetic variety

Pollination

Pollination is often achieved through the use of insects that are attracted to certain colors, structures or scents on the flower. The orchid below is called a Bee orchid and has evolved to actually look like a female bee.

Obviously, it is pollinated specifically by bees.

Economical and Ecological Importance

Economical Importance• Imperative to the field of agriculture in the form of

both product and feed for animals• Human food source• Wood, paper, fiber (cotton, flax, hemp)• Used in the production of some medicines• Decorative landscaping, florist industry• Perfumes and beauty products

Ecological Importance• Food and habitat for wildlife• Soil retention

Leaf Anatomy