Plant Science Portal 
First Vascular Land Plants (2)
 Plant Evolution Tour: Part IV of XV

Although Cooksonia evolved earlier, many consider Rhynia to be the first true vascular terrestrial plant.

Rhynia species, like Cooksonia was an upright plant with dichotomous branching. It was a little taller than Cooksonia, otherwise it was fairly similar.

Rhynia was leafless (as was Cooksonia) and photosynthesis was carried out by all of the green cells in the stems. Unlike Cooksonia, Rhynia had both a phloem for movement of nutrients as well as a xylem for water transport and supporting cortical cells.

Rhynia qwynne-vaughanii fossils have been recovered from the Rhynie Chert in Scotland, UK, which date back to about 400 Ma. Rhynia qwynne-vaughanii grew to about 18cm in height, based on the fossil record and was stabilised by a series of rhizomes from which rhizoids emerged.
An illustration of Rhynia qwynne-vaughanii as interpreted by D.S. Edwards in 1980. The colours are purely speculative.
Another important group of plants in the late Silurian and early Devonian (400 Ma) were the Zosterophylls which included genera such as Zosterophyllum.

Like Rhynia, Zosterophyllum was preserved in the Rhynie Flora of Scotland - an important site of perfect petrifaction of specimens of both genera. Because of this, it is known in explicit detail.

Species of Zosterophyllum such as Z. divaricatum were significant because they had laterally borne sporangia, which means that the sporangia developed along the branches either directly or by attachment to short stem. This species grew to about 30cm and had distinctive H-type branching.
Rhynia gwynne-vaughanii: transverse section of stems. Photo by Hans Steur, used with permission.
Cooksonia, Aglaophyton and Rhynia did not have any leaves however Zosterophyllum did - they were in the form of small scale-like appendages to the stem which became larger, broader and flatter. This effectively expanded the photosynthetic area and gave these plants an advantage.

Zosterophyllum and the Zosterophylls led to Baragwanathia, the Club Mosses, and the Lycopods which are all discussed later on Adam Dimech's Plant Evolution Tour.

After the Palaeozoic Era (235 Ma) the Zosterophylls declined and today are survived by only four genera; Isoetes (Quilworts), Lycopodium, Selaginella (Club Mosses) and Phyloglossum.

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