The Move to Land and Plant Diversity

• More than 280,000 species of plants inhabit Earth today.

• Most plants live in terrestrial environments, including deserts, grasslands, and forests.

• Some species, such as sea grasses, have returned to aquatic habitats.

• Land plants (including the sea grasses) are thought to have evolved from a certain green algae, called charophyceans.

Introduction

What You Need to Live On Land• Supporting Mechanisms

(vascular tissues and lignin)

• Absorptive structures (above and below ground)

• Conducting tissues (Vascular tissues)

• Anti-desiccation Adaptations for Body of plant and Gametes (cuticle and sporopollenin)

• Airborne gamete dispersal

It’s getting hot in here!!!

• There are four main groups of land plants: Mosses (bryophytes), Ferns (pteridophytes), Conifers (gymnosperms), and Flowering plants (angiosperms).

• Multicellular, eukaryotic, photosynthetic autotroph.

• Cell wall of cellulose, storage polysaccharide as starch.

• Chlorophyll a, b, and carotenoids.

• Secrete cuticle to reduce desiccation.

• Most have stomata for gas exchange (except Liverwort)

• Most have seed; embryo with food and protective covering.

• Most have vascular tissues for bulk transport of water and nutrients. Plasmodesmata for transport between cells.

General Characteristics

Non-vascular

aka. Traecheophytes

Naked Seeded Plants

Plants…A Monophyletic

Taxon!

• Land plants share two key ultrastructural features with their closet relatives, the algal group called charophyceans.

The Proposed Ancestors of Land

Plants

• Homologous Chloroplasts. DNA sequences similar, pigments and structure similar.

• Homologous Cell Walls. Formed in similar manner with similar amounts of cellulose. Rosette cellulose-synthesizing complex.

• Homologous Sperm. Some plants have flagellated sperm similar to that of charophyceans.

• Perioxysomes. Help to reduce effects of photorespiration.

• Molecular systematics. Similar nuclear and chloroplast genes.

• Phragmoplasts.

• an alignment of microtubules and Golgi-derived vesicles, during the synthesis of new cross-walls during cytokinesis are perpendicular to cell plate.

• Sporopollenin in charophycean zygote prevents dessication.

• Integral for success of terrestrial plants.

Charophyceans are the green algae most closely related to land plants

• Several characteristics separate the four land plant groups from their closest algal relatives, including:

• apical meristems

• multicellular embryos dependent on the parent plant

• alternation of generations

• sporangia that produce walled spores

• gametangia that produce gametes

3. Several terrestrial adaptations distinguish land plants from charophycean algae

• The elongation and branching of the shoots and roots maximize their exposure to environmental resources.

• This growth is sustained by apical meristems, localized regions of cell division at the tips of shoots and roots.

• Cells produced by meristems differentiate into various tissues, including surface epidermis and internal tissues.

• Multicellular plant embryos develop from zygotes that are retained within tissues of the female parent.

• This distinction is the basis for a term for all land plants, embryophytes.

• All land plants show alternation of generations in which two multicellular body forms alternate.

• One of the multicellular bodies is called the gametophyte with haploid cells.

• Gametophytes produce gametes, egg and sperm.

• Fusion of egg andsperm duringfertilizationform a diploidzygote.

reproductive cell that can develop into a new organism without fusing with another cell.

• Plant spores are haploid reproductive cells that grow into a gametophyte by mitosis.

• Spores are covered by a polymer called sporopollenin, the most durable organic material known.

• This makes the walls of spores very tough and resistant to harshenvironments.

• Multicellular organs, called sporangia, are found on the sporophyte and produce these spores.

• Within a sporangia, diploid spore mother cells undergo meiosis and generate haploid spores.

• The outer tissues of the sporangium protect the developing spores until they are ready to be released into the air.

• The gametophytes of bryophytes, pteridophytes, and gymnosperms produce their gametes within multicellular organs, called gametangia.

• A female gametangium, called an archegonium, produces a single egg cell in a vase-shaped organ.

• The egg is retained within the base.

• Male gametangia, called antheridia, produce many sperm cells that are released to the environment.

• The sperm cells of bryophytes, pteridiophytes, and some gymnosperms have flagella and swim to eggs.

• A sperm fuses with an egg within an archegonium and the zygote then begins development into an embryo.

Fig. 29.9b

1. The three phyla of bryophytes are mosses, liverworts, and hornworts

• Bryophytes are represented by three phyla:• phylum Hepatophyta -

liverworts

• phylum Anthocerophyta - hornworts

• phylum Bryophyta - mosses

• Note, the name Bryophyta refers only to one phylum, but the informal term bryophyte refers to all nonvascular plants.

2. Phylum: Bryophyta (Mosses)Peat bogs used as energy resource, antiseptics,

commercial cropland (cranberry/blueberry)

Gametophyte generation dominant.

Most lack conductive tissues; small, rely on diffusion.

Leaf-like tissues lack cuticle, easy water absorption. (few exceptions)

Bryophyte spores germinate in favorable habitats and grow into gametophytes by mitosis.

The gametophyte is a mass of green, branched, one-cell-thick filaments, called a protonema.

Rhizoids are used for anchorage.

Rhizoids are not composed of tissues.

They lack specialized conducting cells.

Life Cycle of

Typical

Bryophyte

Hornwort

Liverwort

Male Gametophyte

Female Gametophyte

• Modern vascular plants have food transport tissues (phloem) and water conducting tissues (xylem) with lignified cells.

• Have true roots, stems, and leaves.

• Sporophyte generation is dominant and is independent of the parent gametophyte.

• The gametophytes are tiny plants that grow on or just below the soil surface.

• This reduction in the size of the gametophytes is even more extreme in seed plants.

• The first vascular plants, pteridophytes, were seedless.

Traecheophytes: Vascular Plants

• A heterosporous sporophyte produces two kinds of spores.

• Megaspores develop into females gametophytes with archegonia. Produce eggs.

• Microspores develop into male gametophytes with antheridia. Produce sperm.

• A homosporous sporophyte produces one kind of spore that develops into a gametophyte with both antheridia and archegonia on the same structure.

• The seedless vascular plants, the pteridophytes consists of two modern phyla:

• division Lycophyta - lycophytes

• division Pterophyta - ferns, whisk ferns, and horsetails

• These phyla probably evolved from different ancestors among the early vascular plants.

Seedless Vascular Plants

Division: Lycophyta• Club Mosses. Formed forests during Carboniferous

period.

• low-growing understory plants and epiphytes. Most common in wet tropics.

• Leaves each have a single unbranched vein therefore called a microphyll. (Leaves with branched veins are called megaphylls.)

• Special leaves called sporophylls produce a sporangium on top, near the point where they attach to the stem.

• Most species are homosporous, produces a single type of spore.

• This spore develops into a bisexual gametophyte with both archegonia (female sex organs) and antheridia (male sex organs).

Division: Sphenophyta

• One extant genus, Equisetum. Known as horsetail, foxtail, or scouring rush.

• Stores silica in cell wall.

• form underground stems known as rhizomes

• At the tips of reproductive branches are the "cones," or strobili

• Homosporous

Strobilus, spore producing structure

Stem, Internode

Leaves

Lycophyta. The Psilophytes

Division: Pterophyta• Most dominant seedless,

vascular plant.

• large megaphyllous leaves (fronds) with an extensively branched vascular system. Often divided into “leaflets” or pinnae.

• produce clusters of sporangia, called sori, on the back of green leaves (sporophylls)

• Homosporous.

sporangia

indusium

Life Cycle of a Typical Fern

sperm produced in an antheridium must travel through a film of water in order to reach the egg of

an archegonium to form zygote.