Plantae--MossesPhylum Bryophyta (Mike Flaherty)

external image Iceland_04_E_1_35-Moss_Lava_Field.jpg(NG)

Diagnostic characteristics- Moss are nonvascular plants that live on land. Nonvascular plants are plants that do not have a real xylem or phloem. This means each moss cell has to fend for its own nutrients and water. Mosses are a type of Bryophyte along with the hepatophyta (liverworts) and anthocerophyta (hornworts).Mosses develop from multicellular embryos that stays connected to the parent plant. This creates both nourishment and protection for the embryo. Also, moss spores normally produce a protonema when they are germinating. This protonema can then generate a mature, gamete-producing structure, called a gametophore when there are sufficient resources. A mature gametophore produces gametes in gametangia. The gametophyte of mosses has stemlike structures that have many leaflike appendages.

Habitats- Mosses prefer to grow in moist areas or in tree bark, since moisture is needed for moss reproduction. “Moss need a moist environment to reproduce because their sperm must swim, which requires water. Moss also rely on a moist environment because they depend on diffusion in order to get water to their cells.” (SD) They are mostly found in the alpine, tropical, temperate, and boreal forests or wetlands. But they can be found in dry or cold areas like mountaintops, deserts and anarctic and arctic tundra because they can lose the majority of their body water without dying, known as dessication. Mosses are commonly found in terrestrial environments where they help to prevent soil erosion. Mosses can be found in fresh water environments, but have not yet been found in salt water ecosystems. In tundras, mosses actually make up 50-90% of the biomass (CSR 3)
Green tree moss
Green tree moss

Moss growing on a tree. This is a symbiotic relationship. (SI) (9)

Major Types- The major types of moss are polytrichum and sphagnum. Polytrichums are commonly called the hairy cap moss. They have complex “leaves” with ridges that help increase the absorption of water. These "leaves" are shaped like sharp lances and are 6-10 mm long. They are arranged spirally to form star like shapes. Many fungi and rotifers live in these leaves.(KL)(1) Sphagnum is often called peat moss and is found in wetlands. Sphagnum is able to form large deposits of an undecayed organic material called peat. There are an estimated 400 billion tons of organic carbon located in the world’s peatlands. Also they are able to inhibit microbial decay in low temperatures and nutrient levels. They have a resistant phenolic compound embedded into the moss’s cell walls to inhibit this decay.
Sphagnum is the only bryophyte economically important. Sphagnum becomes compacted into peat which, in places such as Scandinavia and Ireland, is dried and used as fuel. Sphagnum has a remarkable capacity to absorb and retain water; it can hold 20-30 times its weight of water. The unusual water-holding capacity of Sphagnum derives from the large hyaline cells in the leaves and, in some species, the dead porous cells of the stem. The closely overlapping, spirally arranged leaves of the branches hold water by capillarity. Also due this tremendous water-holding capacity, Sphagnum is used in packing live plants for shipment, is added to soil to improve its water-holding capacity and has been employed as an absorbing material for oil spills. Because of its absorptive capacity as well as its antiseptic properties which result from the capacity of Sphagnum to increase the acidity of its environment, during World War I and Russo-Japanese wars, Sphagnum was used for the manufacture of surgical dressings. Last interesting fact is the Eskimo used Sphagnum to curb diaper rash. (ZS)

Polytrichum (SR) (7)

Sphagnum (SR) (6)

moss.jpg external image Peat-bog-Ireland.jpg
Picture of moss growing in a forrest. (CC) (11 A peat bog in Ireland. A home of Sphagnum moss. (RL)(15)

Basic Anatomy- Mosses are nonvascular plants which mean they do not have xylem or phloem. They must grow close to the ground because of this. Each moss cell is responsible for obtaining its own water and nutrients as well as performing its own photosynthesis. Most mosses are unable to distribute water and organic compounds within thick tissues because they lack conducting tissues. Mosses are anchored to the ground by delicate and colorless tubular single cells or filaments of cells called rhizoid. Mosses contain sporophytes which consist of a foot, a stalk known as a seta, and a spore producing organ known as a sporangium or a capsule. Mosses also have gametophytes that are typically one or a few cells thick. These gametophytes are multicellular haploids.

Transport of Materials- Most moss cells collects their own nutrients and performs its own photosynthesis. Since they are nonvascular, mosses lack both a xylem and phloem. Moss has a stem-like structure that has many leaf-like appendages. These leaf-like structures are generally only one cell thick and normally lack a cuticle.
Water and nutrients are absorbed by all parts of the plant. This is why they are found in places with a consistent supply of water. Mosses have rhizoids instead of roots. These are branched threads. These threads absorb water. They are also used to anchor the plants. Rhizoids are always multi-cellular and can be extensive. (LW) (14)

Reproduction- Moss contain sporophytes that are green and photosynthetic when they are young but turn a brownish red color when they are about to release their spores. The sporophyte of moss disperses very large amounts of spores. Spore production and meiosis take place in the spore capsule called the sporangium. When these spores are released they may grow and germinate into gametophytes by a process called mitosis. These spores generally produce a one cell thick filament called protonema. When the protonema has enough resources they produce buds that have tissue producing meristems. These meristems are then able to create a structure call a gametophore. A gametophore is a gamete-producing structure. Along with the protonema, gametophores make up the gametophyte body of mosses. The female gametophytes of the moss are known as archegonia and the male gametophytes are known as antheridia. The sperm cell of a moss reaches and fertilizes the egg by swimming through a film of moisture to the archegonium. Then the now diploid zygote divides and develops within the archegonium into an embryonic sporophyte by mitosis. Afterwards the sporophyte develops a long stalk which grows from the archegonium and is attached to and nutritionally dependent on the archegonia. The tip of this stalk is called a sporangium which is where the spores develop. And the spores are able to scatter when the lid of the sporangium pops off. These spores are then able to form protonemata through mitotic division. Finally, the protonemata grow and differentiate until they form sexually mature gametophytes.
(YA)(5)Some moss species hardly ever produce spore capsules, and produce asexually instead . The bulbs, corms, tubers and rhizomes are all parts of certain plants which can grow into new plants by asexual reproduction. There are several different methods in which moss can reproduce asexually such as: when the stem of a large clump of moss dies back, resulting the clump becoming individual plants, or when bits of the stem or even a single leaf from the moss plant are accidentally broken off these bits can then regenerate to form a new plant. Some mosses produce “brood bodies”, which are specialized structures that are actually used to determine the type of moss species.
In Bryophytes, the gametophyte is the dominant, larger, longer living generation, as opposed to the sporophyte. The sporophyte never detaches from the gametophyte to form its own plant, it stays permanently attached to the gametophyte. (JS) (16)

A diagram of the reproductive cycle of mosses. (ZXU)(2)\

external image moss.jpg
Life Cycle of mosses (GR)(4)

Environmental Adaptations- Moss along with the other bryophytes were the only plant that existed for the first one million years that terrestrial communities have existed. Moss are able to survive in harsh environments because the can lose most of their body water without dying. They can then reactivate and rehydrate once moisture becomes available in the environment again. Mosses have large water absorbing cells that allow mosses to absorb up to twenty times its own weight in water. The sphagnum moss releases acidic and phenolic compounds that reduce bacterial activity. Also, Moss disperses its spores through air or water and do not have fruit that animals can eat. One of the main reasons that bryophtes were able to colonize on land was the emergence of the cuticle. The cuticle, a waxy substance that covers the stem like structures and the spores of some species, allows the moss to retain its water. Less water escapes through transpiration with a cuticle. The cuticle also can act as a layer of protection from harmful chemicals and UV radiation. (ORS 12 &13)

Review Questions:

Explain the reproductive cycle of mosses & what happens at each stage?
What are the diagnostic characteristics of Sphagnum moss? (MC)
What characteristics contribute to the success of mosses adapting to their environment? Why is the cuticle so beneficial for bryophytes? (AK)
Mosses are considered to be hearty plants because of there ability to grow in a variety of habitats. Which of their characteristics and/or body systems have helped them to achieve this ability. Explain. (CW)

Reece, Jane B., and Neil A. Campbell. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2009. Print.
2. (ZXU)
3. (CSR)
4. (GR)
5. (YA)
8. (ZS)
10. (NG)
12. (ORS)
13. (ORS)
14. (LW)
15. (RL)
16. (JS)