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. 2021b)

    • 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. 2021b)

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. 2021b)

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

Partitatheca †

  • Edwards et al. 2012

  • Early Lochkovian (Early Devonian) of Shropshire, England

  • Plants with terminal sporangia dehiscing into four valves

  • Sporangial wall comprising longitudinal files of prominent cells, ±stomata

  • Spores are permanent dyads with multilayered wall

    • Outer layer of wall bears sculpture and surrounds both units of the dyad

  • Subtending axes exhibit stomata and are isotomously-branched

P. splendida †(type)

P. horrida †

P. densa †

P. cymosa †