Rhyniophyta

Rhyniophyta
Cooksonia , reconstruction
Temporal occurrence
Upper Silurian ( Pridolian ) to Upper Devonian ( Famennian )
418 to 359 million years
Locations
Rhynie Chert ( Aberdeenshire ) u. a.
Systematics
without rank: Chloroplastida without rank: Charophyta without rank: Phragmoplastophyta without rank: Streptophyta Empire : Plants (Plantae) Department : Rhyniophyta
Scientific name
Rhyniophyta

The Rhyniophyta are a group of extinct plants that are at the base of the vascular plants . They have no leaves, their bare axes branch out forked (dichotomous).

features

The Rhyniophyta have forked (dichotomous) branched shoot axes that do not form leaves. The sporangia are located at the end of the shoot (terminal). The sporangia are ellipsoidal to branched. The axis has a cylindrical protostele as a conductive tissue. The protoxylem is inside (endarch). As far as is known, the spores are all morphologically the same. Therefore it is believed that the species were isospore .

Systematics

The Rhyniophyta were established by Harlan P. Banks (1913-1998) when he recognized that the psilophytes are an extremely heterogeneous group. When dividing the psilophytes, he formed the Rhyniophyta, which in 1992 had the following size:

• Rhyniophytina
  • Rhyniales
    • Rhyniaceae
      • Cooksonia
      • Rhynia gwynne-vaughanii
      • Uskiella
    • Rhyniophytoidae
      • Eogaspesia
      • Steganotheca
      • Salopella
      • Eorhynia
      • Hedia
      • Yarravia
      • Caia
      • Dutoitea
  • incertae sedis
    • Aglaophyton major
    • Horneophyton
    • Taeniocrada decheniana
    • Renalia
    • Nothia
    • Hicklingia
    • Huia
    • Hsua
    • Stachyophyton

The Rhyniophyta, as established by Banks, and as they were described by Taylor and Taylor in 1993, are clearly a polyphyletic group. Some representatives are not even vascular plants. Other representatives, such as some Cooksonia species, are scattered on the basal branches of the vascular plants. Kenrick and Crane established the following cladogram of the basal branches of the vascular plants on the basis of cladistic analyzes:

Polysporangiophytes	Vascular plants    Real vascular plants (eutracheophytes)   Rhyniopsida    Stockmansella      Rhynia      Huvenia      Aglaophyton   Horneophytopsida    Caia      Horneophyton      Tortilicaulis

Kenrick and Crane therefore no longer recognize the Rhyniophyta as a systematic unit, but only place some of their representatives in new groups. Kenrick and Crane put Hsua to the cysterophylls. Aglaophyton is the sister group of vascular plants.

Horneophytopsida

They are the sister group of the clade of aglaophyton and vascular plants. They are the most basic group of the polysporangiophytes.

They have branched sporangia. This characteristic distinguishes it from all other plants. The external shape of the sporangium is very similar to the vegetative axis. Small, multicellular outgrowths sit on the surface of the sporangia. The features are mainly based on the well-preserved Horneophyton fossils . Kenrick and Crane identified two other genera, which they put due to the branched sporangia to the Horneophytopsida. The group thus includes the following members:

• Caia
• Horneophyton
• Tortilicaulis

Rhyniopsida

Rhynia gwynne-vaughanii , reconstruction

The Rhyniopsida are a small group of vascular plants. They are the sister group of all other vascular plants. The branching does not take place in one plane (planar), however, in contrast to higher plants, no regular pattern can be seen. They have a special way of forming adventitious branches: small semicircular outgrowths form on the axes, the vascular bundles of which are not connected to that of the main axis. The sporangia sit at the end on a special tissue cushion (English "pad"). The tracheids are of the S-type that occurs only here: The cell wall is two-layered with a thin inner layer made of non-degradable material and an outer spongy layer. On the entire inner surface there are small, plasmodesmata- sized holes in the cell wall.

According to Kenrick and Crane, the Rhyniopsida comprise the following genera:

• Huvenia
• Rhynia
• Stockmansella

Temporal spread

The oldest finds are those of Caia from the Pridolium , the highest series of the Silurian , which began about 418 million years ago. The most recent finds are from Taeniocrada , which are attributed to the Upper Devonian, which ended 359 million years ago. The Rhyniopsida in the sense of Kenrick and Crane are limited to the Devonian.

Other representatives

Representatives of the Rhyniophyta, some of which have only been poorly researched, are briefly discussed below:

• Uskiella is known from the Siegenium of South Wales. They are bare, evenly forked shoots with ellipsoidal sporangia. The sporangia wall is several layers of cells thick. In the longitudinal direction they have a series of thin-walled cells along which the sporangium ruptures. The spores are alet (have no scars), are 28 to 42 micrometers in diameter and have a two-layer sporoderm.
• Dutoitea is known with several species from the Lower Devonian of South Africa. In the middle of the axis they have a thin median line that could be a vascular bundle or a central strand of a moss plant.
• Steganotheca from the Upper Silurian is around five centimeters tall and branched several times, with each branch ending in a sporangium. Tracheids could not be detected.
• Of Hedia corymbosa , only the distal ends of dichotomously branched axes are known, which have long sporangia at the ends. The finds come from the Lower Devonian.
• In Yarravia , the individual sporangia are combined into simple synangial groups.
• Salopella are dichotomously branched branches, each with a terminal sporangium. The spores are trilet (have a three-pointed scar).
• Taeniocrada from the Lower to Middle Devonian are vascular plants whose axes are flattened, i.e. not cylindrical. They are dichotomously branched, the terminal sporangia are three to seven millimeters long. Some sporangia are also laterally (lateral). The fossils appear in dense mats and have no stomata on the axes. It is viewed by some researchers as an aquatic plant.
• Huvenia from Devonian also has flattened axes. Outgrowths sitting at the forks are interpreted as rhizophores. The sporangia are twisted and stand on their main axes near branches on pads called sporangiophores.
• Renalia hueberi from the Lower Devonian of Gaspé (Quebec) is up to 30 centimeters high and consists of a pseudomonopodial main axis on which dichotomously branching side branches sit, which end in kidney-shaped sporangia. This form of sporangia refers to the Zosterophyllophyta , in the vicinity of which they are also placed by Kenrick and Crane.
• Nothia has bare axes and pear-shaped sporangia. Kenrick and Crane place them near the Lycopodiopsida .

supporting documents

• Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study . Smithsonian Institution Press, Washington DC 1997, pp. 319f. ISBN 1-56098-729-4
• Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants . Prentice Hall, Englewood Cliffs 1993, pp. 191-203. ISBN 0-13-651589-4

Individual evidence

1. ↑ Kenrick, Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study , 1997, part of Fig. 4.31.
2. ↑ Kenrick, Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study , 1997, p. 134.
3. ↑ Kenrick, Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study , 1997, Table 7.5.
4. ↑ after Taylor and Taylor, 1993, pp. 192-195, 201-203.