Horneophytes †

Ecology & Form

• Probably lived in wet, shore environments; grew on sandy, organic-rich soil in damp to wet locations

• Fossils of chytrids, ancient fungi, have been found in the tissue of Horneophyton

Sporophyte (spore-bearing) phase

Horneophyton lignieri †

• Kidston & Lang 1920; Barghoorn & Darrah 1938

Stems

• Upright axes 20 cm tall (2 mm wide) growing from a prostrate corm-like rhizome

  • The rhizome was probably photosynthetic and perennial

  • The aerial axes "...were probably also photosynthetic, sustaining their own limited growth but contributing little, if any, photosynthate to the rhizome" (Kenrick & Long, 2025)

• These aerial axes exhibit equal-branching (isotomous) in distal branches; slightly anisotomous in proximal axes

• Axis tips terminated by sporangia (see reproduction below)

• Stomata are relatively rare and are enclosed by distinctly modified cells (Hass 1991)

• Plants lacked true vascular tissue; "H. lignieri lacks distinct xylem and phloem tissues... Instead, tissues with transfer cell-like structures are prominent, and both cell type and cell wall development vary with position in the plant" (Kenrick & Long, 2025)

  • "...the conducting strand... consists of a solid core of thick-walled cells that differ fundamentally from the tracheids in early vascular plants. These H-type cells exhibit wall ingrowths that range from intricate labyrinths to simpler papillate protrusions, varying in both position and density within the conducting system. Their strong resemblance to transfer cells suggests a primary role in active solute transport, rather than passive water conduction as in tracheids." (Kenrick & Long, 2025)

Roots

• Horneophyton lacks roots but possesses rhizoids emerging from the corm to anchor to the soil

• Evidence of fungal associations (Strullu-Derrien et al., 2014) in the parenchyma of the cortex

  • • Arbuscules from the glomeromycete, Palaeoglomus boullardii †, similar to the living taxon Glomus.

    • Evidence of a mucoromycete, Palaeoendogone gwynne-vaughaniae †, similar in form to the living taxon Endogone. This fungus has thin, branched hyphae populating the plant's corm, forming thicker, coil-like structures between the cells. 

    • In modern plants, these fungi aid in mineral absorption for the plant

Leaves

• Horneophytes were leafless

• It is assumed that the upright stems were photosynthetic, although this may have been localized for supporting sporangia and spore production.

Reproduction

• Spore-bearing plants with sporangia that are stem-like (cylindrical) and the sporangia are forked

  • Forked sproangia are unique to this group, but some eophytes 

• Bumps or emergences are on the sporangia

• Central column of sterile tissue (=columella) found in the "horn" (=sproangium)

  • Similar (homologous?) to Aglaophyton †, hornworts, and mosses

• Spores were released through a slit at the top of each lobe

  • Spores were trilete meiospores with short conical protuberances

• The chytrid taxon, Rhizophydites matryoshkae †has been found preserved on the spores of Horneophyton (Krings et al., 2021) as a probable parasite