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 and sperm during fertilization form a diploid zygote. 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 harsh environments.

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.