Rhyniophytes †

Earliest true vascular plants

The rhyniophytes are a group of extinct spore-bearing vascular plants that were leafless and rootless plants, with upright branching stems. This group is the earliest known representatives of the tracheophyte clade, possessing true vascular tissue. This group gets its name from the locality from which they are found in Rhynie Scotland. The Rhynie Chert shows exquisitely preserved fossils, providing evidence of the entire life cycle of Rhynia. These plants had ground-creeping rhizomes, that gave rise to upright determinate stems. Unlike most plants of the Devonian, they had adventitious branching with latent "buds" or branches. In addition, this locality provides evidence of the gametophyte phase.

Features

Sporophyte (spore-bearing phase)

Stems

  • Similar to the early polysporangiophytes, such as Aglaophyton, these plants show increasing diversification of stem types. These early plants are constructed with indeterminate and determinate structures like modern plants.

  • Determinate aerial stems: above ground, upright stems which terminate in sporangia for dispersal

  • Indeterminate rhizomes: ground-running, or below ground portions, that creep similar to vegetative propagate the population

    • Vesicular arbuscular mycorrhizae found in the cortex of Rhynia rhizomes

  • Adventitious branching: latent "buds" or branches, which could elongate to make new stems, similar to modern plants.

  • Vascular tissue present, but not the same as eutracheophytes (see S-type tracheids below)

Classification

Embryophytes

└Polysporangiophytes

└Tracheophytes

└Rhyniales †

Rhyniophytes are basal tracheophytes

Geologic Age


Left: Reconstruction of Rhynia gwynne-vaughanii

Below:: Piece of Rhynie chert showing Rhynia axes

Right: Cross-section of a Rhynia axis showing haplostele

Leaves

  • Leafless; assumed by some to have photosynthetic stems and/or rhizome.

  • Boyce (2008) has questioned whether the upright stems were photosynthetic in Cooksonia, which would probably pertain to the rhyniophytes as well.

  • Gametophyte may have been the main photosynthetic portion of lifecycle

Reproductive Structures

  • Spores in sporangia; Homosporous

  • Abscission layer at base; attached to pad of tissue

Gametophytes (gamete-bearing phase)

  • Form genus Remyophyton delicatum

  • This phase may have been the main photosynthetic portion of the plant's lifecycle

  • Dioicous*, bearing male and female gametangia (antheridia and archegonia) on different axes

    • *Note that in gametophytes, the term is "dioicous", not "dioecious" as in sporophytes

  • Gametophyte axes are vascular, unlike all gametophytes of modern pteridophytes (except for Psilotum)

Above (left): Reconstruction of a stand of Remyophyton delicatum; Above middle: Close-up of antheridia of Remyophyton; Above right: Close-up of archegonia of Remyophyton

Diversity

Calyculiphyton blanai †

  • Remy et al. 1991

  • Emsian

  • Compression fossil with elongate axes that terminate in cup-like structures

  • May represent a gametophyte

Celatheca beckii †

  • Hao et al. 1995

  • Pragian of Posongchong Formation of eastern Yunnan, China

  • Leafless axes dividing anisotomously

  • Sterile lateral axes dichotomize two or three times, terminating in recurved tips

  • Fertile lateral axes dichotomize to produce a group of four sporangia

  • Each sporangium exhibits an outer leaf-like bract which folded around the sporangium

  • Celatheca resembles the Australian fossil Yarravia

Eddianna gaspiana †

Eogaspesiea gracilis †

  • Daber 1960

  • Tangled mess of branching axes that reached 10 cm in length, probably from a rhizome

  • Alete spores had thin walls

Eocooksonia sphaerica †

  • Xue et al. 2015

  • Originally Cooksonella (Senkevitsch, 1978; Doweld 2000)

  • Upper Silurian (Pridoli) of Xinjiang, Northwest China and Central Kazakhstan

  • Pseudomonopodial branching pattern, which forms an apparent main axis with lateral dichotomously branching systems.

  • Specimens demonstrate terminal sporangia with a central body and a border with four to eight elongate-triangular emergences

Hedeia †

  • Cookson 1935

  • Early Devonian from Victoria, Australia, Kazakhstan and China

  • Erect axes terminating in corymbose clusters of erect sporangia

  • H. corymbosa (Cookson 1935)

  • H. parvula (Jurina 1969)

  • H. sinica (Hao 1998)

Huvenia kleui †

  • Hass and Remy 1991

  • Pragian of the Rhenish Massif

  • Leafless axes that appear to be flattened and branch dichotomously

  • The strand of conducting tissue contains simple tracheids

  • The sporangia are borne on the ends of short branching stems (sporangiophores) rather than terminating main stems as in some other early land plants

  • The gametophyte of this plant may be Sciadophyton

Monnowella bennettii †

  • Morris & Edwards 2014

  • Early Devonian (Lochkovian) of Welsh Borderland, UK

  • Axes with isotomous or weakly anisotomously branching

  • Single sporangia terminating unbranched laterals

  • Sporangia were terminal and ellipsoidal

Above: Monnowella bennettii † (from Plate II, Morris & Edwards 2014)

Rhynia gwynne-vaughanii †

  • Kidston & Lang 1917

  • From the Rhynie chert in Aberdeenshire, Scotland

  • Rhizomatous plant with upright isotomous axes

  • Possible deciduous lateral branches were used to disperse laterally over the substrate and stands of the plant may therefore have been clonal populations

Above: Reconstrcution of Rhynia gwynne-vaughanii †

Salopella †

S. australis † Tims & Chambers 1984

  • Late Silurian (Ludlovian) - Early Devonian (Pragian) of Victoria, Australia

  • Axes with at least 2 dichotomies (0.9-2.4 mm wide)

  • Plants at least 145 mm tall

  • Sporangia 6.5-14.0 mm long and 1.3-2.0 mm wide

S. cf. marcensis (Edwards et al. 1994).

Salopella

Above: Plate 32 (Tims & Chambers 1984) of Salopella australis

Sciadophyton †

  • Remy et al. 1980

  • Early Devonian compression fossils

  • Gametophytes of rhyniophyte plant, bearing gametangia

  • Axes that radiate from a basal corm-like thallus that terminate in cup-like structures

  • Possibly the gametophytes of either Stockmansella or Huvenia (Kenrick et al. 1991, Remy et al. 1993), but it may be the gametophyte stage of several land plants

  • Sc. laxum ((Dawson 1871; Steinmann 1928)

  • Sc. palustre (Istchenko 1965)

  • Sc. steinmannii (Steinmann; Kräusel and Weyland 1930)

    • This species is thought to belong to the sporophyte Zosterophyllum rhenanum

Above: Compression fossil of Sciadophyton

Steganotheca striata †

  • Edwards & Rogerson 1979

  • Silurian (Ludlow) of Powys, Wales (Edwards & Rogerson 1979)

  • Plant exhibiting elongate sporangium terminating a short length of parallel-sided, unbranched axis.

  • The diagnostic features of S. striata sporangia, the obliquely running striations and the terminal thicker lens-shaped region are usually clearly visible.

  • In the majority of specimens the distal region persists, the organic material of the main body of the sporangium has flaked off leaving dark strands adhering to the rock surface

Above: Plate 1 (Edwards & Rogerson 1979) showing Steganotheca striata sporangium showing surface striation

Stockmansella †

  • Fairon-Demaret 1986

  • S. langii † (Fairon-Demaret 1985)

    • Ribbon-like axes bear lateral sporangia.

    • The sporangia are fusiform and attached to the axis by a pad of tissue, circular in outline, which most probably functioned as an abcission layer.

      • Sproangia dehisce along a specialized longitudinal slit which is clearly distinguishable from the more or less numerous splitting lines.

    • The conducting strand is composed of helically strengthened S-type, cylindrical elements which are of various diameters

  • S. remyi (Schultka and Hass 1997)

    • Eifelian (youngest member of Rhyniaceae)

  • The gametophyte of this plant may be Sciadophyton

Yarravia †

  • Lang & Cookson 1935

  • Pragian of Victoria, Australia

  • Axes 2 to 2.5 mm in diameter, and up to 7.5 cm in length.

  • No examples of branching or anatomy known

  • The sporangia born radially in groups of 5-6 at the ends of axes.

  • Base of sporangia are fused together, but tips may be free; the entire structure can be described as a synangium

  • Y. oblonga (Lang & Cookson 1935)

    • In Y. oblonga, the synangium (the group of fused sporangia) was longer than wide, being about 7 mm long by 1.25 mm wide. The tips of the sporangia were free and appear to consist of tissue not containing spores.

  • Y. subsphaerica (Lang & Cookson 1935)

    • The synangium of Y. subsphaerica was significantly larger and as long as wide, being about 1 cm in length and width. The tips of the sporangia were less prominent

  • Y. minor (Danzé-Corsin 1956)

  • Y. gorelovii (Ananiev 1960)