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PLANTS PART IV

EVOLUTIONARY INNOVATIONS IN PLANTS

Series of Adaptations

  1. Non-Vascular Plants

  2. Seedless Vascular Plants

  3. Seed Plants (Gymnosperms)

  4. Seed Plants (Angiosperms)

GYMNOSPERMS

  • Overview:

    • Gymnosperms appear early in the fossil record approximately 305 million years ago.

    • They dominated Mesozoic terrestrial ecosystems from 251 to 65.5 million years ago.

    • Gymnosperms were better suited to drier conditions than non-vascular plants.

Ecological Role

  • Served as food for herbivorous dinosaurs.

  • Recent fossil discoveries indicate that gymnosperms were pollinated by insects over 100 million years ago.

  • Angiosperms began to replace gymnosperms near the end of the Mesozoic era, around 66 million years ago.

Dominance in Current Ecosystems

  • Presently, most terrestrial ecosystems are dominated by angiosperms, though conifers are still prevalent in specific regions, such as:

    • Northern latitudes

    • Boreal forests

PHYLA OF GYMNOSPERMS

Phylum Overview

  • Gymnosperms are classified into four phyla:

    1. Cycadophyta (cycads)

    2. Ginkgophyta (one living species: Ginkgo biloba)

    3. Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia)

    4. Coniferophyta (conifers such as pine, fir, spruce, larch, and redwood)

Phylum CYCADOPHYTA

  • Characteristics:

    • Palm-like leaves

    • Large cones

    • Possess flagellated sperm (unlike most seed plants)

    • Once abundant during the Mesozoic; currently, few species exist, many of which are endangered.

PHYLUM GINKGOPHYTA

  • Key Facts:

    • Contains a single extant species, Ginkgo biloba.

    • Also possesses flagellated sperm.

PHYLUM GNETOPHYTA

  • Composition:

    • Includes three genera: Gnetum, Ephedra, and Welwitschia.

    • Species exhibit variation in appearance; some thrive in tropical climates, while others adapt to desert conditions.

PHYLUM CONIFEROPHYTA

  • Overview:

    • Largest of the gymnosperm phyla.

    • Most conifers are evergreens, allowing them to photosynthesize year-round.

Examples of Conifers

  • Notable species include:

    • Douglas fir

    • Sequoia

    • European larch

ANGIOSPERMS

  • Characteristics:

    • Produce flowers and fruit as reproductive structures.

    • Most widespread and diverse of all plant groups with approximately 250,000 species (making up 90% of extant plant species).

PHYLUM ANTHOPHYTA

  • Definition:

    • The single phylum of angiosperms.

    • Flowers are specialized structures for sexual reproduction.

    • Many species are pollinated by animals; some rely on wind for pollination.

FLOWER STRUCTURE

  • Overview:

    • Flowers are specialized shoots with up to four types of modified leaves known as floral organs:

    1. Sepals: Enclose the flower

    2. Petals: Typically brightly colored to attract pollinators

    3. Stamens: Produce pollen

    4. Carpels: Produce ovules

Detailed Anatomy of Floral Organs

  • Stamen:

    • Composed of two parts:

    • Filament: The stalk component

    • Anther: The part that produces pollen

  • Carpel:

    • Composed of three parts:

    • Ovary: Located at the base, it holds the eggs

    • Style: The structure leading to the stigma

    • Stigma: The sticky surface that receives pollen

COMPOSITION OF FLOWERS

Types of Flowers

  • Can be categorized as complete or incomplete:

    • Complete Flowers: Contain all four organ types.

    • Incomplete Flowers: Lack one or more of the organ types.

Symmetry in Flowers

  • Flowers can exhibit different types of symmetry:

    • Radial Symmetry: Symmetrical around center (e.g., daffodil).

    • Bilateral Symmetry: Symmetrical on one side (e.g., orchid).

FRUIT

  • Formation and Function:

    • Fruits form when the ovary wall thickens and matures, serving to:

    • Protect seeds

    • Aid in dispersal

    • Fruits can be classified into two categories:

    1. Fleshy Fruits

    2. Dry Fruits

Mechanisms for Seed Dispersal

  • Mechanisms of dispersal include:

    • Explosive Action: Seeds are ejected from the fruit.

    • Animal Dispersal: Seeds within edible fruits are eaten and later excreted.

    • Wind and Water: Seeds can be carried to new locations via wind or water.