rhynia

Also found on some early plants such as Rhynia, where they are hypothesized to aid in photosynthesis.

As Rhynia major the species had been placed in the rhyniophytes, but no alternative higher level classification was proposed for the new genus.

According to the cladogram, the genus Rhynia illustrates two steps in the evolution of modern vascular plants.

Genera such as Rhynia have a similar life-cycle but have simple tracheids and so are a kind of vascular plant.

A. major was first described by Kidston and Lang in 1920 as the new species Rhynia major.

(The other species of Rhynia,R. gwynne-vaughanii, was not affected.)

The Rhynia plant was small and stick-like, with simple dichotomously branching stems without leaves, each tipped by a sporangium.

Three genera were initially included, Rhynia, Horneophyton and Psilophyton.

As the diagnosis of Rhynia was that it was a vascular plant, he created a new genus, Aglaophyton, for this species.

Accordingly he transferred it to a new genus as Aglaophyton, leaving R. gwynne-vaughnii as the only species of Rhynia.

Currently, Rhyniopsida includes the genera Huvenia, Rhynia, and Stockmansella, all from the Devonian.

A centrarch (protoxylem in the center of a metaxylem cylinder) haplostele is prevalent in members of the rhyniophyte grade, such as Rhynia.

Colonized fossil roots have been observed in Aglaophyton major and Rhynia, which are ancient plants possessing characteristics of vascular plants and bryophytes with primitive protostelic rhizomes.

In 1917 Kidston and Lang found the remains of an extremely primitive plant in the Rhynie chert in Aberdeenshire, Scotland, and named it Rhynia.

So while Silu-Devonian plants such as Rhynia and Horneophyton possessed the physiological equivalent of roots, roots - defined as organs differentiated from stems - did not arrive until later.

From a carpet of moss-like gametophytes, the larger Rhynia sporophytes grew much like simple clubmosses, spreading by means of horizontal growing stems growing rhizoids that anchored the plant to the substrate.

Like those of Aglaophyton major, Horneophyton lignieri and Nothia aphylla the gametophytes of Rhynia are dioicous, bearing male and female gametangia (antheridia and archegonia) on different axes.

Evidence of the gametophyte generation of Rhynia has been described in the form of crowded tufts of diminutive stems only a few mm in height, with the form genus name Remyophyton delicatum.

The simple form echoes that of the sporophyte of mosses, and it has been shown that Rhynia had an alternation of generations, with a corresponding gametophyte in the form of crowded tufts of diminutive stems only a few millimetres in height.

The class was established in 1917, under the name Psilophyta, with only three genera (Rhynia, Horneophyton and Psilophyton) for a group of fossil plants from the Upper Silurian and Devonian periods which lack true roots and leaves, but have a vascular system within a branching cylindrical stem.