Lecture 16: Angiosperms

Flower

structure of modified leaves—>some are sporophylls

• basis of modern taxonomy

• grouping together species with similar floral characteristics

Fruit

seed bearing structure, ovary tissues encircle the ovule

angio=case

sperm=seed

Ovary

tissues that encircle the ovule

Albian-Aptian gap

Dominant plant Gymnosperms-Angiosperms (over 35 MY)

• soil condition changed to favor angiosperm species

• gymnosperms are limited to more extreme environments where angiosperms can’t thrive

  • angiosperms have short growing seasons so won’t do well in cold areas

Angiosperm Dicots

aka eudicots (largest group)

Characteristics:

• 2 cotyledons (upon germination)

• netted venation in leaves

• Unique organization of stem, root, leaf tissues

• taproot mainly

• flower petals in multiples 4-5

Dicots: Asteraceae

Sunflower family

• largest plant family

Flower shape:

• radially symmetrical

• petals are modified smaller flowers with ovules

Dicots: Fabaceae

legume family- 3rd largest

Fruit shape:

• bean “pod” (called legume)

• any plant with legume=Fabaceae family

Legume

bean “pod”

Dicots:Cucurbitaceae

Cucurbit family

• some are important commercial crops!(melon, cucumber, squash)

Fruit characteristics:

• three chambers with row of seeds on the interior

Cucurbit

fruit structure: 3 chambers with row of seeds on the interior

Dicots: Rosaceae

rose family

• many are commercial crops!

  • almost all fruit trees!

  • apples, pears, cherries, etc

• Flowers:

• - radially symmetrical flowers with MANY petals

Angiosperm Monocots

2nd largest group

Characteristics:

• 1 cotyledon upon germination

• parallel venation in leaves

• unique organization of stem, root and leaf tissues

• fibrous root system

• flower parts in multiples of 3

Monocots: Orchidaceae

Orchid family

Characterized by:

• showy bilaterally symmetrical flowers

• tiny seeds with no endosperm

Monocots: Poaceae

Grass family

Characteristics:

• reduced flowers

• mainly wind pollination

  • flowers don’t need to be showy

• long, narrow leaves

• Apical shoot meristem at the BASE of the shoot

  • NOT the tip

  • because herbivores duh

Magnoliid

only one family: Magnoliaceae

Magnoliid: Magnoliaceae

simplified flowers

• examples of early angiosperms

Includes magnolias

Basal angiosperms

aka ANITA (acronym of 5 families)

• Representative of earliest forms of angiosperms (debatable)

• Water lilies and Hellebores

ANITA

Acronym of 5 basal angiosperms families

• Amborellaceae

• nympheales

• austrobaileyales

Male lifecycle

Similar to gymnosperms

• single celled microspore produced

• microspore undergoes mitosis

  • forms pollen (multicellular haploid organism)

Difference: fertilization aspect

• pollen lands on stigma of flower

• Pollen grain germinates

  • pollen tube extends down style to micropyle

• generative cell releases 2 sperm cells

  • sperm cells=male gamete

Angiosperm lifecycle-Female

VERY different from gymnosperms

• after production of initial megaspore

Differs in

• presence/absence of archegonia

• structures produced by gametophyte

• Ovule contents

• Most common type of pollination

• what is fertilized by sperm cells

Within the flower:

• mother diploid cell—>meiosis

  • 4 daughter cells, 3 die, 4th=megaspore

• megaspore → mitosis→ DIRECTLY produces female gametophyte

  • NO archegonia

• further mitosis: single egg produced, +other cells to develop seed

  • Synergids, antipodals, the central cell with the polar nuclei

Angiosperm Lifecycle

Pollination RIGHT after fertilization

Double fertilization

Each pollen cell releases: 2 sperm cells

• One sperm cell

  • fertilizes egg

  • becomes zygote

• Other sperm cell

  • fertilizes zygote

  • becomes endosperm

Stigma

part of male lifecycle

Style