Tag Archives: Bryophyta

Friday Fellow: Pellucid Four-Tooth Moss

by Piter Kehoma Boll

It’s time to go back to the tiny ones, the mosses. The third species of this group to be featured here is called Tetraphis pellucida or the pellucid four-tooth moss. Found in the northern hemisphere, this species is common in deciduous forests and grows almost exclusively on decaying wood of coniferous trees.

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The general appearance of the pellucid four-tooth moss on a decaying log. Photo by Hermann Schachner.*

The pellucid four-tooth moss can have two different modes of reproduction: sexual and asexual. The sexual reproduction occurs in a way similar to that found in most mosses. The asexual one, however, is somewhat peculiar and happens through the production of propagules called gammae. Gemmae can occur along a stalk, being called stalk gemmae, or inside a cup formed by three to five large leaves, a structure called gemmae cup. Gemmae from both stalks and cups are propelled by the power of raindrops. What is interesting is that the type of gemmae structure seems to be related to the inclination of the surface in which the moss grows. From a horizontal surface to one with an inclination of about 18°, cups are more common, possibly because a water drops falling inside a cup propels the gemmae with great speed upward. On surfaces with inclinations above 18°, stalks are more common, as a cup lying on its side wouldn’t be very useful, and water can wash down gemmae from stalks more easily.

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A closer look showing several gemmae cups. Photo by Hermann Schachner.

Regarding dispersal, spores from sexual reproduction seem to be able to move farther away from the mother, but they are not as successful in germinating and occupying a new substract as gemmae. Thus, the different reproduction modes seem to help this amazing little moss to spread by adapting to the most adequate means.

However, when other moss species arrive at the substrate, the pellucid four-tooth moss is rapidly replaced. It has, therefore, a very low success when competing with other species. How can it be one of the most common species in its habitat then? Well, it is so because the specialized propagules of the pellucid four-tooth moth allow it to quickly colonize newly-formed substrates, which arise from the common disturbances on the forest floor. No other species can colonize that quickly, but as they can easily dislodge our fellow, there is an endless struggle to survive. The pellucid four-tooth moss relies on disturbance to go on.

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References:

Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. I. Population density and reproductive mode. The Bryologist 94(3): 255-260. https://doi.org/10.2307/3243962

Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. II. Differential Success of Sexual and Asexual Propagules. The Bryologist 94(3): 284–288. https://doi.org/10.2307/3243966

Kimmerer, R. W. (1993) Disturbance and dominance in Tetraphis pellucida: a model of disturbance frequency and reproductive mode. The Bryologist 96(1): 73-79. https://doi.org/10.2307/3243322

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Friday Fellow: Field Hornwort

by Piter Kehoma Boll

Three weeks ago our Friday Fellow was a moss, being the third non-vascular plant to be introduced. And before going back to vascular plants, let’s take a look at another non-vascular fellow from the only non-vascular division that was not yet introduced here, the hornworts.

The species I chose to start the participation of hornworts is the field hornwort, Anthoceros agrestis.

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A piece of soil with the field hornwort growing on the top. Photo by Wikimedia user BerndH.*

As with other hornworts, the field hornwort has a dominant gametophyte phase which appears as a small flattened plant growing very close to the soil. The sporophyte grows over it and has the form of an elongate vertical horn, hence the name hornwort.

Found in Europe and North America, the field hornwort usually grows in wet places and is often surrounded by  mosses. Its gametophyte has some internal cavities filled with muscilage that are a favorite place for species of cyanobacteria of the genus Nostoc to grow. This association is what makes hornworts acquire their slight bluish tinge.

The field hornwort has the smallest genome of all non-vascular plants studied until the present and because of that it has been cultivated to serve as an interesting model organism.

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ResearchBlogging.orgReferences:

EOL – Encyclopedia of life. Field Hornwort. Available at <http://eol.org/pages/399515/overview&gt;. Access on May 18, 2017.

Szövényi, P., Frangedakis, E., Ricca, M., Quandt, D., Wicke, S., & Langdale, J. (2015). Establishment of Anthoceros agrestis as a model species for studying the biology of hornworts BMC Plant Biology, 15 (1) DOI: 10.1186/s12870-015-0481-x

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Friday Fellow: Spreading Earthmoss

by Piter Kehoma Boll

If you still think mosses are uninteresting lifeforms, perhaps you will change your mind after knowing the spreading earthmoss, Physcomitrella patens.

Found in temperate regions of the world, except for South America, but more commonly recorded in North America and Eurasia, the spreading earthmoss grows near water bodies, being one of the first species to colonize the exposed soil around pools of water. Although widely distributed, it is not a common species.

Physcomitrella_patens

The spreading earthmoss growing on mud. Photo by Hermann Schachner.

Since the beginning of the 1970s, the spreading earthmoss has been used as a model organism, especially regarding gene manipulation. Differently from what occurs in vascular plants, the dominant life phase in mosses is the gametophyte, an haploid organism, meaning it has only one copy of each chromosome in its cells. This is an ideal condition for the study of gene expression, as the activation or inactivation of a gene is not hindered by a second one in another copy of the chromosome in the same cell.

Physcomitrella_patens_ecotypes

Physcomitrella patens growing in the lab. Credits to the Lab of Ralf Reski.*

By controlling gene expression in the spreading earthmoss, researches can track the role of each one of them in the plant’s development. Comparing these data with that known from flowering plants, we can have a better understanding of how the plant kingdom evolved.

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ResearchBlogging.orgReferences:

Cove, D. (2005). The Moss Physcomitrella patens Annual Review of Genetics, 39 (1), 339-358 DOI: 10.1146/annurev.genet.39.073003.110214

Schaefer, D. (2001). The Moss Physcomitrella patens, Now and Then PLANT PHYSIOLOGY, 127 (4), 1430-1438 DOI: 10.1104/pp.127.4.1430

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Friday Fellow: Silvergreen Moss

ResearchBlogging.orgby Piter Kehoma Boll

Found throughout most of the world, you probably have encountered this fellow many times in your life, but did not pay any attention. After all, it is just a moss!

Scientifically known as Bryum argenteum and popularly named silvergreen moss, this tiny little fellow lives on cracks of stones, walls and sidewalks, thus it is also known as sidewalk moss. It usually forms small lumps composed by many plants growing tightly together. The small leaves of each plant are also tightly packed together, giving it the appearance of a small piece of wool thread. The tip of the plant usually have a silver tinge that may be more or less intense, hence the name silvergreen moss.

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This is the general appearance of the silvergreen moss. Lumpy and soft. Photo by flickr user harum.koh*

As with all mosses, the green tapestry that forms the main part of the silvergreen moss are gametophytes, haploid organisms that are either male or female. The males produce a male gamete that swims towards a female plant and fertilizes its gamete. As a result, a new sexless plant grows on the top of the female, the so-called sporophyte. You can see the sporophytes as small stalks with a bag on the end.

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A bunch of sporophytes growing on top of the gametophytes. Photo by Paul van de Velde.*

Extracts of the silvergreen moss has shown antimicrobial activity, being effective against several species of bacteria and fungi, making it a promising candidate for the development of new medicines.

Living from the poles to the equator, the silvergreen moss has a huge ability to adapt to extremes of temperature, humidity and altitude. It also shows a considerably high tolerance to heavy metals, and that is most likely the reason why it is so common along roads.

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References:

EOL – Encyclopedia of Life. Bryum argenteum. Available at < http://eol.org/pages/864280/overview >. Access on September 29, 2016.

Sabovljevic, A., Sokovic, M., Sabovljevic, M., & Grubisic, D. (2006). Antimicrobial activity of Bryum argenteum Fitoterapia, 77 (2), 144-145 DOI: 10.1016/j.fitote.2005.11.002

Shaw, A., & Albright, D. (1990). Potential for the Evolution of Heavy Metal Tolerance in Bryum argenteum, a Moss. II. Generalized Tolerances among Diverse Populations The Bryologist, 93 (2) DOI: 10.2307/3243622

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