Life on Earth Kingdom Plantae Part 5 Division Anthophyta (Flowering Plants or Angiosperms)

Life on EarthKingdom Plantae

Part 5

Division Anthophyta

(Flowering Plants or Angiosperms)

Division: Anthophyta• Largest group in the Plant Kingdom with

more than 300,000 species• Seed plants with no archegonia produced• Gametophyte generation highly reduced (7

cells and 8 nuclei in the female and 2 cells and 3 nuclei in the male)

• Double fertilization occurs with the formation of endosperm (for nutrition)

Division Anthophyta (cont.)

• Species produce “flowers” which are often showy with colored petals and or sepals (modified leaves)

• Close co-evolution with animal pollinators• Two major classes are recognized:

– Liliopsida (monocots)– Magnoliopsida (dicots)

Monocots vs. Eudicots

• Only one cotyledon in the embryo

• Leaves with parallel veins

• Flower parts in 3’s• Stem with an

atactostele• No true secondary

growth• Pollen monocolpate

• Two cotyledons in the embryo

• Leaves with “net veins”

• Flower parts in 4’s and 5’s

• Stem a eustele• Many with

secondary growth• Pollen tricolpate

Monocots

Includes:

Iris, grasses, palms, orchids, sedges, yuccas, agaves, lilies

Eudicots

Includes:

Poppies, sunflowers, buttercups, oaks, mints, and just about everything else!

Flower Structure

• A “typical” flower has:–petals– sepals– carpels– stamens

Trillium

Variations on Floral Structure

• Primitive flowers are those with many, separate parts with both stamens and carpels

• More “advanced” flowers have undergone “fusion” of parts and reduction in numbers of each part; some have separate male and female flowers

• With these changes other terms are needed to describe these variations

Terminology

• All the petals of a flower = COROLLA• All the sepals of a flower = CALYX• All petals AND sepals = PERIANTH• All stamens = ANDROECIUM• Fused carpels = PISTIL• All female parts = GYNOECIUM

Flower DiagramHypogynous Flower

Arrangement of Floral Parts

• All parts attached below the ovary = SUPERIOR OVARY or a HYPOGYNOUS FLOWER

Arrangement of Floral Parts

• All parts attached above the ovary = INFERIOR OVARY or a EPIGYNOUS FLOWER

Arrangement of Floral Parts

• Flower parts attached to a floral cup or HYPANTHIUM = PERIGYNOUS FLOWER

Epigynous Flower

What parts are present?

• PERFECT FLOWERS have both stamens and carpels

• IMPERFECT FLOWERS produce only stamens (staminate flowers) or only carpels (pistillate flowers)

• COMPLETE FLOWERS have all 4 flower parts (stamens, carpels, petals, sepals)

• INCOMPLETE FLOWERS lack one or more parts

Floral Symmetry

Actinomorphic = radial symmetry

Zygomorphic = bilateral symmetry

How are the flowers arranged on the plant?

• The flowering branch is called the inflorescence

• Many types of arrangements are known (umbel, cyme, corymb, raceme, spike, panicle, and HEAD)– The HEAD is found in members of the

sunflower family (Asteraceae)– Composed often of TWO flower types = DISC

FLOWERS and RAY FLOWERS

Head of aSunflower

Ovary

The HEAD Inflorescence

Ray flower

Disc flowers

Other Inflorescences

Penstamon (a thyrse)

Daucus (a compound umbel)

Lilac (panicle) and Delphinium (raceme)

Life Cycle of Angiosperms(In the Ovule)

• Surrounded by the integuments, the megaspore mother cell (2N) undergoes meiosis producing 4 megaspores

Life Cycle of Angiosperms(In the Ovule)

• Three of the four megaspores die, and one functional one divides 3 times by mitosis forming 8 nuclei (N)

• Cell walls are formed making 7 cells with 8 nuclei (mature embryo sac or female gametophyte)

Life Cycle of Angiosperms(The Female Gametophyte)

EGG CELL

SYNERGID CELLS

ANTIPODAL CELLS

POLAR NUCLEI

Angiosperm Life Cycle(Lily variation: one of many)

• Meiosis produces 4 megaspore nuclei• Three of the nuclei FUSE (3N)• Two mitotic divisions follow forming the

final female gametophyte (embryo sac)• The (3) antipodal cells are triploid• The synergid cells and egg are haploid• One polar nucleus is 3N, the other 1N

Lilium (4-nucleate stage)

Lilium Female Gametophyte

EGG CELL

SYNERGID CELLS

ANTIPODAL CELLS

POLAR NUCLEI

Lilium (8-nucleate stage)

Life Cycle of Angiosperms(In the Anther)

• Microspore mother cells (2N) undergo meiosis to form microspores (N)

• Microspores divide once by mitosis forming pollen grains (male gametophytes)– TWO cells are present (tube cell and a

generative cell)– outer wall (with sporopollenin) is the exine and

the inner wall is the intine

Lilium anther (xs)

Mature Pollen Grains

Generative Cell

Tube Cell

ragweed pollen grain

Exine of Lilium Pollen

Life Cycle of Angiosperms(Pollination)

• Pollen grains are released from the anther and carried (pollination) to the carpel/pistil of the flower or different flower

Life Cycle of Angiosperms(Toward Fertilization)

• Pollen grain germinates and a pollen tube extends down through the style leading to the ovule

• The generative cell divides and two sperm nuclei are released into the ovule

Life Cycle of Angiosperms(Fertilization)

• One sperm nucleus fuses with the egg nucleus and this zygote will grow to become the embryo

• The other sperm nucleus fuses with the polar nuclei forming the primary endosperm nucleus which develops into the endosperm

• This process is called DOUBLE FERTILIZATION

Double Fertilization

sperm nucleiegg nucleus

n polar nucleus

3n polar nucleus

Summary

• Therefore, the embryo (the next sporophyte generation) is diploid (2N)

• The endosperm tissue, used for nutrition of the embryo, is 3N (2 polar nuclei + sperm nucleus)

• Endosperm may be 5N (or other N’s) as in Lilium (3N polar nucleus + 1N polar nucleus +1N sperm nucleus)

Summary (cont.)

• The integument layers, which surround the female gametophyte mature to become the seed coat

• Ovule (with the embryo and endosperm) becomes the seed

• The ovary of the flower matures to become the fruit