Eophytes

Eophytes are an ancestral and transitional group of land plants that were recently named (Edwards et al. 2021a; Edwards et al. 2021b). They had branching sporophytes, with food-conducting cells, but lacked water-conducting cells. Thalloid fossils associated with the branched forms may be female gametophytes that transferred nutrients to the sporophytes. It is possible that the sporophytes were non-photosynthetic, and obtained nourishment from the gametophyte through transfer cells.

Form & Ecology

Eophytes were very small plants that possessed a distinctive combination of transitional features for early land plants
Fossils are formed of charcoal, which was a product of one of the earliest incidences of wildfire in the geological record (Edwards & Axe 2004; Glasspool et al. 2006)

Sporophyte (Spore-bearing phase)

Stem

The sporophyte phase of the life cycle was simple, comprising bifurcating axes measuring < 1 mm in diameter
Eophytes had an internal vascular system composed of food-conducting cells and a plicate epidermis with occasional stomata (Edwards et al., 2021)
- These plants did not have water-conducting cells which arose with the protracheophyte aglaophytes

Leaves

Leafless aerial axes

Roots

Unknown, but assumed to be rootless with rhizoids at least in the gametophyte

Reproduction

The axes bore terminal, valvate sporangia, in which permanent polyad spores developed
These spores are known as permanent cryptospores in the dispersed fossil record

Gametophyte (gamete-forming phase)

Thalloid fossils in the locality are found in association with these branched sporophyte forms
These thalloid fossils were composed almost entirely of cells with labyrinthine ingrowths, which were probably transfer cells, based on comparison with modern embryophytes
These also were present in sporophyte fossils where they were associated with putative food-conducting cells
It is quite possible that these thalloid forms are female gametophytes that were providing nutrients to the sporophytes

Above: Two hypotheses on the relationships among living bryophytes (hornwort, liverwort, moss) and tracheophytes ("Trach") with the most significant support in molecular phylogenetic analyses (Puttick et al., 2018). FCC = food-conducting cells; WCC = water-conducting cells; "Aglo" = Aglaophytes; Eo = Eophytes (from Fig. 8, Edwards et al., 2021)

Classification

Embryophytes

└Polysporangiophytes

└Eophytes †

Geologic Age

Early Devonian (Lochkovian) of the Welsh Borderland
Probably arose during the Early or Middle Ordovician, based upon cryptospores

Above: Fertile specimens of eophytes from Welsh borderland (from Fig. 2, Edwards et al. 2021)

Above: Labyrinthine network of elongating and branching wall ingrowths fusing with neighboring ones (from Fig. 4, Edwards et al., 2021)

Partitatheca †

Edwards et al., 2012
Early Lochkovian (Early Devonian) of Shropshire, England
Plants with isotomously-branched sporophytes
Plants with terminal sporangia dehiscing into four valves
Sporangial wall comprising longitudinal files of prominent cells, ±stomata
Spores are permanent dyads (sometimes permanent tetrads) with multilayered wall
The outer layer of the wall bears sculpture and surrounds both units of the dyad
Subtending axes exhibit stomata

P. cymosa †

Edwards et al., 2012
Fusiform sporangium, at least 1.05 mm long and 0.43 mm wide, splitting into four valves
Spores, 31–36 mm wide, with sparse sculpture of spines forming star-shaped rosettes or with occasional fusion between adjacent elements
Spores assigned to Cymbohilates cymosus

P. densa †

Edwards et al., 2012
Plant with bullet-shaped terminal sporangium at least 1.35 mm and 0.6 mm wide dehiscing into valves
Spores with crowded spinous sculpture are permanent dyads
Spores assigned to Cymbohilates horridus complex but to a new morphon not recognized in the dispersed spore record

P. horrida †

Edwards et al., 2012
Elongate sporangium at least 0.9 mm long and 0.5 mm wide, with rounded tip, splitting into four valves
Spores, 49–58 mm diameter, with sculpture of spines, sometimes in groups, joined by ridges at their bases to form an irregular reticulum
Spores assigned to Cymbohilates horridus var. horridus

P. splendida †(type)

Edwards et al., 2012
Globular sporangium at least 850 mm wide, dehiscing into four valves.
Occasional stomata, 30 mm long by 10 mm wide, on proximal parts of the wall.
Spores with complex multilayered ultrastructure and spinous sculpture, 58–68 mm in diameter, are permanent dyads.
Spores assigned to Cymbohilates horridus var. splendidus Richardson

Page updated

Google Sites

Report abuse