Bryophytes- Nonvascular Plants •
•
Bryophytes are small plants that typically grow in moist areas. The bryophytes that are most familiar to you are probably mosses, which can be found growing in forests all over the world. Bryophytes have several common characteristics: The gametophyte generation is the dominant, or most visible, generation. Bryophytes need water from rain or dew in order to reproduce.
Bryophytes- Nonvascular Plants
The water content of the plant body is about equal to that of the environment. When conditions are dry, the plants dry out, but don’t necessarily die. When conditions are wet, the plants begin to grow again.
Bryophytes- Nonvascular Plants Bryophytes, which are organized into three phyla, all have certain characteristics in common: - The gametophyte is the dominant phase of the life cycle.
Bryophytes- Nonvascular Plants Structures called antheridia produce sperm, and the archegonia produce eggs. They require water for reproduction so the sperm can swim to the egg. The structure of the plant body is simple and typically lacking vascular tissue like xylem and phloem. They release their spores from elevated sporangia.
Phylum Hepatophyta - Liverworts •
•
•
Liverworts can be flat, lobed plants like the one in the diagram, or they can be leafy and look more like mosses. Liverworts got their name because people in the Middle Ages thought the lobed liverworts looked like the liver from a person. Wort is an old word for “plant,” so liverwort literally means “liver plant.”
Phylum Hepatophyta - Liverworts •
Liverworts - Structure and Form The simple, flattened bodies of lobed liverworts are called thalli. The thallus of a lobed liverwort is different on the top and the bottom. - The top surface has pores that are used for gas exchange. The pores remain open at all times. - The lower surface has little root-like structures called rhizoids that are made from single cells. Rhizoids help anchor the liverworts to the ground. Some liverworts also have multicellular scales on their bottom surface.
•
Phylum Hepaticophyta - Liverworts Some thallose liverworts, such as Marchantia, have a fairly complex internal structure. The pores lead into airy pockets called air chambers that contain little stacks of photosynthetic chlorenchyma cells. Layers of nonphotosynthetic parenchyma cells form the bottom of the thallus.
Section of Marchantia Thallus - Liverworts
Life Cycle of Liverworts •
•
Liverworts begin as haploid spores. When a spore lands in a moist environment, it begins to grow by mitosis, producing a filament of cells called a protonema. One cell, called the apical cell, continues to produce new cells by mitosis to form a haploid thallus. Sexual reproduction occurs when the haploid thallus produces gametangia called antheridia and archegonia.
Life Cycle of Liverworts •
•
•
Antheridia produce sperm. Antheridia are little chambers on the surface of the thallus that become filled with many sperm cells. Archegonia produce eggs. Archegonia are little vase-like structures that form on the surface of the thallus. Each “vase” contains an egg cell at the bottom. Because the thallus of liverworts is already haploid, sperm and eggs are produced by mitosis, not meiosis.
Life Cycle of Liverworts •
•
•
When water is available, the sperm use their flagella to swim to the eggs of a different liverwort plant and fertilization occurs, producing a diploid zygote. The zygote divides by mitosis to produce an embryo that develops into the diploid sporophyte. Liverwort sporophytes are small club-shaped are small club-shaped structures that grow out of the archegonia that they were formed in.
Life Cycle of Liverworts •
•
•
Cells within the sporophyte called spore mother cells divide by meiosis to produce spores, completing the liverwort life cycle. Liverworts can also reproduce asexually by gemmae, little groups of cells seen in cuplike structures called gemmae cups. The gemmae can be splashed out of the cup by rain drops and grow into a new plant.
Asexual Reproduction of Marchantia - Liverworts
Life Cycle of Liverworts- Marchantia
In Marchantia, the antheridia and archegonia are lifted up on little stalks, producing umbrella like structures called gametophores. –phor means to carry, and these structures will carry gametes.
Life Cycle of Liverworts- Marchantia
• The male gametophore is called the antheridiophore. The top of the antheridiophore in Marchantia looks like a flat disk. • The female gametophore is called the archegoniophore. The top of the archegoniophore in Marchantia looks like the top of a palm tree.
Life Cycle of Liverworts- Marchantia •
•
The sporophyte that develops after fertilization is designed to produce spores and then eject them over a wide area. The sporophyte has three main regions: The foot attaches the sporophyte to the archegoniophore.
Life Cycle of Liverworts- Marchantia The seta is a short thick stalk that suspends the rest of the sporophyte from the archegoniophore. The capsule is the main part of the sporophyte
Life Cycle of Liverworts- Marchantia •
•
Cells found in capsule….. Elaters- long, pointed cells that change shape rapidly, helping to eject spores; change shape in response to changes in humidity, twisting and untwisting to push out spores
Life Cycle of Liveworts - Marchantia •
•
Calyptra- layer of cells that protects sporophyte until it is mature, breaks open at maturity Spore mother cellsundergo meiosis to produce spores.
Leafy Liverworts Leafy liverworts….. • are often abundant in tropical forests and in fog belts. • Always have two rows of partially overlapping “leaves” whose cells contain distinctive oil bodies. • “Leaves” often have folds and lobes.
Leafy Liverworts •
Archegonia and antheridia are produced in cup-like structure. At maturity, sporophyte capsule may be pushed out as the seta elongates. Germinating spore produces a protonema.
