Life on Earth
Kingdom 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
• 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
vs.
Eudicots
• 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 Diagram
Hypogynous 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 a
Sunflower
Ovary
The HEAD Inflorescence
Ray
flower
Disc
flowers
Other Inflorescences
Daucus (a compound umbel)
Penstamon (a thyrse)
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
POLAR
NUCLEI
ANTIPODAL
CELLS
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
POLAR
NUCLEI
ANTIPODAL
CELLS
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
Tube Cell
ragweed pollen grain
Generative Cell
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
egg nucleus
sperm nuclei
3n polar nucleus
n 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