Kingdom Plantae: MossesSruti Parvataneni
Diagnostic Characteristics
Mosses are part of the phylum Bryophyta, in the kingdom Plantae. Three phyla in the plant kingdom, Phylum Hepatophyta, Phylum Anthocerophyta, and Phylum Byophyta, are known as bryophytes. Most bryophytes are known as non-vascular plants because they don't have cells that are joined into water and nutrient-transporting tubes, i.e. vascular tissue. Bryophytes evolved from algal ancestors, and were probably the first plants that were terrestrial. There are about 12,000 existing species of moss: they are the most common type of bryophyte. They are also the type of bryophyte that is most closely related to vascular plants. They are part of the plant kingdom, so mosses are multicellular, eukaryotic, photosynthetic autotrophs. They form the soil in sucession.(rj)
Notice that the bryophytes, or non-vascular plants appeared before the vascular plants. Green algae is the ancestor of all terrestrial plants.

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Mosses are terrestrial plants, though they lack many of the terrestrial adaptations that vascular plants possess.
They are most common in moist and wet habitats because they lack conducting tissue which can distribute the water
and nutrients within the thick tissues. Also, the moss gametophytes are usually only a few cell layers thick, so they
are found near water and dissolved minerals, and they grow very close to the ground, only a few inched tall. Mosses
are anchored to the ground by rhizoids (in mosses, filaments of cells) which are not made of tissues, lack specialized
cells which can transport water or organic compounds, and do not help mineral or water absorption. So, they are not like
vascular plant roots. Mosses especially depend on the wind dispersion of their moss spores, which are haploid in nature
and are fertilized to create moss individuals wherever they land. Moss diversity and wide distribution can be attributed to
spore dispersion. Moss survive best in moist alpine, boreal, temperate, and tropical forests and wetlands because of the
ample supply of water. On the other hand, mosses are able to live in cold or dry environments because of their ability to
lose much of their water capacities without dying, and their ability to reactivate and hydrate their cells when water is available again. Thus, mosses live in more extreme environments such as mountaintops, the arctic and antarctic tundra, and deserts. (Similar conditions most likely faced moss ancestors: the earliest land plants.) Furthermore, moss cell walls have certain tools named phenolic compounds which absorb dangerous amounts of UV and other short-length radiation present in deserts and high altitudes and latitudes.

Mosses are found in almost every habitat: from deserts, streams to the Arctic. (AR)

Moss in an unlikely desert environment (JP)
Moss in an unlikely desert environment (JP)

In some polar lakes, moss covers the lake bottom to great depths. In Artic and Antartic lakes, these mosses are often the only multicellular plants present! (IL)

Major Types
The major and most common types of moss are the Polytrichum and the Sphagnum.
A common form of the moss is the "hairy cap" moss Polytrichum. It has more complex "leaves" with ridges that help absorb sunlight better because they are coated with cuticles. It also possesses conducting tubes at the center of its "stem" to transport water and organic compounds. So, it is capable of growing quite tall (up to 2 meters high): it seems to be an exception in the class of moss.
In addition, the Sphagnum moss is a wetland moss that forms peat, which is large deposits of undecayed organic material. The regions where sphagnum moss forms are called peat bogs, and the high-latitude boreal regions inhabited by this moss are called peatlands. Sphagnum moss does not decay readily because of the phenolic compounds (mentioned earlier) that it contains in its cell walls. It also secretes phenolic (containing phenol, a caustic, poisonous, crystalline compound) and acidic substances which help reduce surrounding bacterial activity. Peat bogs typically have low temperatures and nutrient levels, so microbial decay is prevented. Sphagnum moss used to be used by aboriginal people for diapers, and as natural antiseptic packaging for wounds. In modern times, it is used as a soil conditioner and for packaging plant roots in shipments. The moss is used so often because of its ability to absorb 20 times its weight in water when it is dry: it has huge, dead, water-absorbing cells.

Sphagnum Moss
Sphagnum Moss

Polytrichum Moss
Polytrichum Moss

Basic Anatomy
As discussed earlier, mosses are nonvascular plants, so they lack the lignified vascular tissue which enables other land plants to transport water and nutrients in tubes within itself. Lignin is a coating present in vascular plant xylem (a type of transport tissue in vascular plants). Moss grows close to the ground because of the absence of a vascular tissue and the fact that its "leaves" are usually only one to a few cell layers thick and lack a cuticle to keep moisture lacked in. They are anchored to the ground by rhizoids, filaments of cells, which, unlike land plant roots, do not assist in water or nutrient transport.
Mosses contain gametophytes and sporophytes. Gametophytes are multicellular, haploid structures which undergo alternation of generations and produce gametes (sperm and egg). Alternation of generations is expanded upon in the "Reproduction" section. The gametophytes have stem-like structures and leaf-like projections one cell thick. The few-cell structure of moss' gametophytes allow for the transfer of water and nutrients because the cells are located near the materials the plant needs. Gametophytes are the dominant phase of the life of moss, and are larger than the sporophytes, which are present only part of the time a moss lives. Sporohytes are diploid and perform meiosis. Meiosis is a type of cell division that results in two daughter cells each with half the number of chromosomes of the parent cell. Most importantly, sporophytes produce spores: reproductive cells that can develop into multicellular organisms through mitosis without fusing with other cells. Mitosis is a type of cell division that results in two daughter cells each identical to the parent. Sporophytes rely on the gametophytes to which they're attached for sugars, amino acids, minerals, and water.
Next, the sporophyte is made of the foot, the seta, and the sporangium (also called the capsule).
The materials from the parent moss are gathered by the foot, transported (conducted) by the seta, which elongates to the capsule. This capsule uses the resources to produce spores and disperses the spores with the aid of the wind. Mosses have the simplest sporophytes that become tan or brownish-red as they prepare to release their spores. A Spore that begins to germinate develops into a protonema: a green, branched, one-cell-thick filament that is able to absorb water and nutrients efficiently due to its large surface area. Then, the protonema produces buds containing meristems, which produce the mature, gamete-producing structure called a gametophore. The protonema and the gametophore compose the gametophyte body of a moss.

The organism that we identify as moss is actually moss in its gametophyte generation phase, which is its dominant phase. (MR; Source 17)

Mosses do not produce flowers, but in many species of Mosses, the Antheridia, the male reproductive organ, looks like a green flower head. (AR)

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Note the bigger, more conspicuous appearance of the gametophyte.
Note the bigger, more conspicuous appearance of the gametophyte.

Transport of Materials
Since mosses do not have the xylem and phloem (vascular tissue) that vascular plants do, they exchange materials directly with the outside environment with their one-cell to a few cells-thick leaves. Polytrichum is an exception, as stated earlier, and possesses conducting tissues in the center of its “stem”, which helps transport materials throughout the moss. Their "leaves" are actually single-cell thick leaf-like appendages, but without cuticles, so water cannot be conserved. Even the rhizoids which anchor moss to the ground do not help in any water or nutrient transport.

Some mosses have water transport cells called hydroids and fat solute conducting cells called leptoids. The reliance on diffusion restricts moss size. (PS Source 15)

When the bryophyte gametophores mature, they produce gametes in the gametangia, the reproductive organ of bryophytes. Eggs are produced in the female reproductive organ, the archegonia, while sperm are produced in the antheridia, the male reproductive organ. The antheridia and archegonia are types of the gametangia and are protected by tissues (not vascular). The sperm must travel to the female plant, as the two organs are located with their respective gender of plant. So, they are released into a water film when they reach the female plant, and make their way to its archegonia with the aid of chemical attractants. The eggs of the archegonia are not reelased, but when the sperm finally reach the eggs, a zygote forms (gametes fuse) and stays within the female gametangia. The sporophyte develops from the zygote, receiving nutrients from the parent through the placental nutrient cells. In bryophytes, the offspring develop from multicellular embryos that remain attached to the "mother" plant, which nourished and protects the embryos. The capsule releases its calyptra, a protective cap of gametophyte tissue, when the moss sporophytes are ready to release their spores. Therefore, the upper part of the capsule, the peristome, is now uncovered and controls the dispersion of spores, so they are released at a gradual rate. This is an adaptation by the mosses to take advantage of the changing winds. After the spores are released, the responsibility of spore dispersion is left completely to the air currents. Once the spores land, they germinate by mitosis, forming the small, green protonemata, as discussed earlier. Then, the protonema create buds with meristems, which produce the mature, gamete-producing structure called a gametophore. The protonema and the gametophore compose the gametophyte body of a moss.

Eggs come in two forms, they are either small and also released into the water where they are eventually found by a sperm. Or else they are larger and retained within the animals body, in ooecia in those forms that have them. These are then fertilized by sperms that are brought in on the feeding current. In this later case the larvae are released after they hatch. These larvae can swim but do not feed. They swim towards the light at first then after a few hours they swim away from the light, down to the sea floor to look for a suitable substrate to start a new colony on. Most species of Bryozoans practice some form of brood care such as this.The eggs of those species which do not brood their eggs, are much smaller (about 1 tenth the size) and much more numerous than the eggs of those species which do brood their eggs. Having been fertilized in the open sea they become part of the plankton. Here they hatch into a 'Cyphonautes' larvae which spends 1 to 2 months in the plankton feeding and growing until they too are large enough to descend to the substrate and start a new colony. (RW)(MS 14)

external image lifecyclemoss.ethan.jpg(AP)

Mosses can also reproduce asexually. Asexual reproduction occurs through the process of fragmentation. During fragmentation any part of the gametophyte plant is capable of regenerating the protonemal phase followed by a mature gametophyte. Leaves, stems and rhizoids will all produce new protonema if the environment is favourable. (RW)

The equivalent of sperm in Mosses is antherozoids. (AR)

In the sporophyte phase, the moss develops a food for an anchor and getting food and nutrients, as well as a sporangium, a capsule holding the mother cells as they undergo meiosis. The sporangium looks like a little brown pod that sprouts from the moss. (LPE)

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Above is a diagram of a moss embryo. (CP source 8)

Life Cycle of Polytrichum

This is another diagram that details the life cycle of a typical moss plant. The more the merrier! (MR; Source 18)
This is another diagram that details the life cycle of a typical moss plant. The more the merrier! (MR; Source 18)

Environmental Adaptations

Mosses are a type of bryophyte, and were probably the Earth's only terrestrial plants for the first 100 million years that terrestrial communities existed. Perhaps to encounter the harsh and extreme conditions of Earth's atmosphere then, moss have adapted mechanisms to help them survive with little water. Mosses can lose most of their body water without dying, and then rehydrate and reactivate their cells when moisture becomes available. This is why they can survive in extreme conditions, like at high altitudes, and deserts, all the while preferring moist and wet environments. Moreover, the peristome of a moss is an adaptation that helps in the organized and gradual dispersion of moss spores, so that the changing wind conditions are accounted for and taken advantage of. Plus, the peristome teeth, usually composed of cell wall remnants, respond to changes in the humidity of the atmosphere, and help in controlled dispersion.

Calliergon giganteum, also known as the Artic moss, is an example of a specie which has evolved to better suit its environment. This plant's long life and it's short growth is a product of the harsh winter conditions as well as the short growing conditions. (RK)

Mosses came before both angiosperm and gymnosperm. One adaptionmade by mosses to its environment was the ability to reproduce with spores,
reproductive structures that are adapted not only for dispersal but also surviving for extended periods of time in unfavorable conditions. (MB)
Spores do have certain advantages in that they are so lightweight, wind can carry them for long distances. The downfall of the spore, however, is ironically the result of its tiny size. Because spores are so small, they cannot store as much food for developing mosses. (VN)
Mosses lack a vascular tissue or stem and are in shady areas. (MP)

Here are some nice summary videos: :)

Mosses are not well represented in the fossil record, in part because their soft tissue cannot be well preserved. However, the earliest identifiable fossil is from the early Carboniferous period, which was about 320 million years ago. (MR; Source 17)

Review Questions:
1. How is it advantageous for mosses to act as soil? (JS)
2. How have mosses adapted, in terms of their anatomy and other apparent characteristics, to survive under harsh conditions with little water? (TB)
3. What is the best habitat for mosses to grow? (MM)
4. How do polytrichum and sphagnum mosses differ? (Matt B)
5. Identify and explain the major types of mosses. (CM)
6. Identify the differences between a Gametophyte and Sporophyte and describe how the two are essential for reproduction. (ZJ)


AP Biology: Learn The Moss Life Cycle - YouTube. YouTube - Broadcast Yourself. Web. 23 Oct. 2011. <>.

"Bryophytes of Stanley Park | Some Basics of Bryophytes." Web. 23 Oct. 2011. <>.

Campbell, Neil A., and Jane B. Reece. "Campbell Biology." Pearson Education, Inc. Web. 23 Oct. 2011. <>.

Conrad, Jim. "Mosses." Backyard Nature with Jim Conrad. 05 Oct. 2009. Web. 23 Oct. 2011. <>.

Fenwick, David. "Polytrichum Species - Haircap Mosses (Moss Images)." APHOTOFLORA - Part of the A-P-H-O-T-O Wildlife Stock Image Libraries. Web. 23 Oct. 2011. <>.

Investigating Woodland Moss - Exploring Oak Woodland (5/6) - YouTube. YouTube - Broadcast Yourself. Web. 23 Oct. 2011. <>.

Reece, Jane B. "Chapter 29: Plant Diversity I: How Plants Colonized Land." Biology: Sixth Edition. By Neil A. Campbell. 6th ed. San Francisco: Benjamin Cummings, 2002. 575-94. Print.

8. (CP) (RW) (AR)

9. "Mosses." Backyard Nature with Jim Conrad. Web. 11 Nov. 2011. <>. (VN) (LPE)

10. (AP)
11. (MP)
12. "Amazing Arctic Moss.",, (10/29/01)
13. (RW)
Kosasihiskandarsjah. "Moss Reproduction - YouTube." YouTube - Broadcast Yourself.Web. 13 Nov. 2011. <>.
(MS) (JP- picture)

15. (IL)

17. "Moss." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Science In Context. Web. 3 Dec. 2011.18. Life history of mosses. N.d. INTRODUCTORY BIOLOGY II. East Stroudsburg Univeristy, n.d. Web. 3 Dec. 2011. <>.