Cooksonia

Sonia Cook, reconstruction

• Worldwide

Cook Sonia is a fossil plant genus that is mainly known from the Silurian. Their representatives are therefore one of the oldest known land plants.

Features

Cook Sonia were only a few inches high. The naked axes were dichotomously ( dichotomous ) branches, possessed stomata and had an outer ring of thickened cells ( Sterom ). Sporangia were terminal ( terminal), the spores were thick-walled. The axes possessed genuine vessels ( tracheids ).

System

The genus Cook Sonia is traditionally made to the Rhyniophyta. However, it is highly polyphyletic: while some species are basal representatives of Eutracheophyten, Cook Sonia is near the Bärlapppflanzen Cambrensis. Some types are:

• Cook Sonia pertonii among others from the late Silurian ( Pridolium ) of Hertfordshire, England, or the early Devonian ( Lochkovian ) of Shropshire, England, known. The stem axis may be unbranched, naked and have an outer layer of thick-walled cells ( Sterom ). There are not received water-conducting cells. The epidermis of the axis are elongated slit openings. The epidermal cells of the sporangium are rounded or angular. Sporangia are oval, while wider than high. They are terminal and have no discernible opening structures. The microspores are trilet ( three-rayed scar ). Cook Sonia pertonii stands as well as the following way quite at the base of Eutracheophyten ( cf. cladogram in vascular plants ).

• Cook Sonia caledonica is inter alia from the Lochkovian of Angus, Scotland, known. The axes are naked and evenly dichotomously branched at least four times. Anatomy or cuticle are not known. Sporangia are oval to kidney-shaped, are terminally and may open into two equal flaps. Spores and gametophyte are unknown.
• Cook Sonia Cambrensis has been described from fragmentary fossils of the lower Red Marl Group of Freshwater East Bay, Dyfed, Wales, from the late Silurian ( Pridolium ). The axes are naked and at least once evenly branched dichotomously. Anatomy, stomata or cuticle properties are not known. The sporangia are circular to elliptical and are terminal. Opening mechanisms are not known.
• Cook Sonia hemisphaerica was described from the lower Old Red Sandstone of Shropshire, England, from the Lochkovian. The axles are up to 6.5 centimeters long, naked and branch out at least once uniformly dichotomous. The axle diameter is about 1.5 mm. Sporangia are semi-spherical to elliptical and are terminal. The stomata are not known. The microspores are spherical, smooth, and 23 to 35 microns in diameter.

• Cook Sonia banksii was only in 2002 from the Lower Devonian ( Lochkovian ) of Shropshire, England described. The spore -containing area is included here in the extended peak region of the axis. The cavity is lined by a smooth, non-cellular layer. Significantly cells are found only on the sporangia edge. The spore count Avitus to Ambitisporites.

Temporal and geographical distribution

Cook Sonia was found in Wales in deposits from the Middle Silurian ( Ludlow ) and are therefore up to 423 million years old. Sonia Cook -like sporangia from Ireland are dated to the Wenlock ( 428 million years). The finds date back to the Lower Devonian Emsian, which ended 397 million years ago.

Fossils of the genera were found virtually worldwide, but mostly in areas of the former continent Laurasia, such as the U.S., Canada, Scotland, the former Czechoslovakia, Wales, Libya and Siberia. Finds some of South America are rare.

Botanical history

The genus was named by William Henry Lang by Isabel Clifton Cookson, a paleontologist.

Documents

• Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study. Smithsonian Institution Press, Washington, D.C. 1997, pp. 324-326. ISBN 1-56098-729-4
• Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants. Prentice Hall, Englewood Cliffs 1993, pp. 191f. ISBN 0-13-651589-4