Tuesday, January 4, 2011

Selaginella denticulata, the moss fern

Ferns of the genus Selaginella, along with Lycopodium and Isoetes are the most primitive vascular plants and oldest currently exist on Earth, as appeared about 150 million years before dinosaurs, in the Carboniferous period. Their evolutionary ancestors, the Lycophyta, reach the size of large trees with a trunk and woody branches covered with leaves up the stem. They lived on coastal wetland soils in a tropical climate, making it easier to reproduce by spores. The remains of these extraordinary plants became our largest deposits of coal.

Selaginella denticulata sprouting vigorously in February on the substrate held between several stones from a wall facing north patch in the shade of some oak trees.

The Selaginella denticulata looks like a moss ground cover with dorsoventrally flattened stems, creeping, bearing four rows of ovate leaves denticulate edge of different sizes according to their position: the two lateral rows are higher than the ridges. Is sterile and fertile stems stems with sporangia called strobili. Its genome has 18 chromosomes.

Their creeping growth and ground cover allows you to live and colonize many habitats, provided they are cool and shaded, but with enough light, avoiding direct sunlight, surfaces and cracks of rocks and stones, as an epiphyte on trunks and branches of old trees with rough bark and a bit of substrate in the form tufted floor covering permanently wet, etc. .. Along with lichens, liverworts and true mosses with which it shares the same habitat, plant substrate is formed by decomposition of the older layers and juxtaposition of a new one every year, growing on decomposed layer of the previous year.

Shoots of Selaginella denticulata crawling over the surface of a moist, shaded boulder in October. Several of the outbreaks, generally the most vigorous and erect, are fertile and are called strobili, which means an outbreak with sporangia. The two photos above are made in the Valley of Soller on the island of Mallorca.

Selaginella denticulata carpeting dripping rock on the island of Madeira in May. This species is distributed throughout the Mediterranean and Macaronesia, except the Cape Verde archipelago.

The leaves of sterile shoots, like the left, are called microphyllous. Those of the strobili or fertile outbreaks, such as the right, are called microsporophyllus if surrounding a microsporangium with male microspores and megasporophyllus if surround a  megasporangium  with female megaspores.

Details of microphyllous, equivalent to the normal pinnae of a fern, seen under a microscope at 40 magnification.

Small spines or denticles over the edge of the microscope micrófilo at 100 magnification. These spines give the name of "denticulata".

Roots of Selaginella denticulata, called rhizophores, allowing you to look hard at low substrate on which they live and penetrate into the crevices of the rocks looking for nutrients and moisture. These are very useful rhizophores spread Selaginella, which multiplies easily booting an outbreak in a pot and planting it, for example, a bonsai as if it were moss. (Double click on the photo to enlarge)

Macro image of a strobilus or fertile outbreak with the male red sporangia or microsporangia in the distal and the female yellow sporangia or megasporangia in the proximal part.

Male microsporangia a vivid red containing microspores grouped in fours, ie what is called a tetrads. Picture taken at 40 magnification.

Tiny spores curious male with triangular structure (trilete). Have recently dispersed red color, which changes to brown earth to rust. Photo taken at 400 magnification.

Female megasporangia a bright yellow lemon with three or four large megaspores inside. I shoot so that they can be cut with a scalpel or the leaves finely megasporoplyllus around them. Picture taken at 40 magnification.

Female megaspores of Selaginella denticulata under the microscope at 40 magnification. Are ten times larger than the male spores or microspores.

One of the previous megaspores view at 400 magnification, the same gains as in the photo of the male microspores. It is very striking difference in size.

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