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
Branching is isotomous, anisotomous, and even pseudomonopodial
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)
Haplostele with centrarch maturation and S-type tracheids (i.e. annular or helical thickenings made of spongy material)
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
Compression fossil with elongate axes that terminate in cup-like structures
May represent a gametophyte
Celatheca beckii †
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 †
Emsian of Gaspe, Canada
2mm in diameter with well-developed terete S-type xylem
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 †
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 †
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 †
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).
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 †
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)
