RHYNIA

CLASSIFICATION OF RHYNIA

Kingdom :- Plantae

Division :- Pteridophyta

Sub-division :- Psilophytopsida

Class :- Rhyniopsida

Order :- Rhyniales

Family :- Rhyniaceae

Genus :- Rhynia

COMMENTS :-

Rhynia is a fossil member (not found living in the present age), discovered from Rhynichert Beds (or upper Devonian era) in Aberdeenshire of Scotland, by Kidston and Lang in 1917.
The two species R. major, about 40-50 cms in height and R. gwynne-vaughani, about 20 cms in height, found at this station, were well preserved, hence their form and structure are well known.
The plant grew in swampy marshes. It was differentiated into horizontally creeping rhizome and an upright branched shoot without leaves.
There were no roots. Unicellular rhizoids were borne in patches, on underside of the rhizome.
The upright branches were dichotomously branched and gradually tapering. The sporangia terminated these branches.

Rhynia. External features of the plant.

COMMENTS :-

Both aerial branches and rhizome were differentiated into epidermis, cortex and stele.
The epidermis was cuticularized with stomata scattered on the aerial shoot. They were absent from the rhizome.
The cortex was differentiated into outer and inner zone.
The outer cortex was only 1-4 layered and had compact parenchymatous cells.
The inner cortex had spherical cells with large intercellular spaces. The inner cortex is believed to be the chief photosynthetic region of the plant.
The stele was a typical protostele with xylem completely surrounded by phloem.

Rhynia. T.s. of rhizome (a part is shown cellular).

COMMENTS :-

It was nearly oblong in shape, broad at the base and pointed at the apex.
The wall of the sporangium was several layered, of which two could be easily distinguished.
The outer wall was cuticularized and the innermost acted as tapetum.
Inside the sporangium were spores, all of which were of the same size. Spores in tetrads were also seen in some specimens.
Columella was absent from the sprangium.

DIVISION – Pteridophyta
1. True roots generally present (except in Psilopsida),
2. True vascular strand present.
Sub-division :- Psilophytopsida
1. True roots absent.
2. Shoot differentiated into subterranean rhizome and apical portion.
3. Sporangia borne terminally.
4. Homosporous.
Order – Psilophytales
1. Sporophyte dichotomously branched.
2. Sporangia generally borne singly.
Family – Rhyniaceae
1. Rhizoids unicellular, on rhizomes.
2. Aerial portion leafless.
Genus – Rhynia
1. Subterranean portion not corm-like.
2. No columella in sporangia.