Drepanophytes †

Geologic Age

• Late Silurian - Late Devonian (Early Mississippian)

• Baragwanathia † is the oldest known drepanophyte

• Their height of diversity was the Early Devonian

• Hestia may have been one of the last drepanophytes

Classification

   └Eutracheophytes

    └Lycophytes

     └Lycopsida

      └Drepanophycales †

Ecology & Form

• Herbaceous plants growing in wetland environments

Stems 

Morphology

• • Upright stems with isotomous & anisotomous branching; probably determinate shoots

  • Small lateral buds on aerial axes

  • Prostrate rhizomes that were presumably indeterminate

Anatomy

• Vascular plectostele or actinostele

• Exarch in maturation

• Asteroxylon has a four-lobed (star-shaped) vascular stele

Roots

• Long-lived, below-ground root-bearing axes producing large clones that helped the plants survive frequent sediment burial in well-drained soils within a seasonal wet-dry climate zone

• Asteroxylon possessed both root-bearing axes (rhizophores?) and quasi-roots (Hetterington et al., 2021)

Leaves

• Leaf-like enations in some (e.g., Asteroxylon), microphylls in other taxa (e.g., Drepanophycus)

  • In Asteroxylon enations, the vascular trace (xylem/phloem) stops at the base of the enation and does not enter it

Reproduction

• Reniform (kidney-shaped) sporangia

• Not associated with a sporophyll as in derived lycopods

• Not aggregated into cones

Hestia eremosa †

• Bateman et al., 2007

• Lower Carboniferous (Tournasian) from Oxroad Bay, East Lothian, Scotland

• Axes of apparently herbaceous lycopsid, up to 5 mm in diameter. 

• Stele ranging from 40% of axial diameter in small axes to 20% in larger axes, radial, exarch, stellate

  • 7–10 rounded lobes separated by moderate to deep troughs, each lobe expanding slightly to strongly radially before terminating in a single protoxylem strand

  • Metaxylem tracheids of broadly similar diameter except where approaching the protoxylem strands, 20–35 μm in diameter, scalariform pits partly infilled with perforated sheets; 

  • Protoxylem tracheids are also scalariform but lacking perforated sheets, 5–12 μm in diameter

  • Dense inner cortex more or less contacts protoxylem strands, separated by narrow cylindrical void from wider (17–23% of axial diameter) outer cortex

• Small, tangentially expanded leaf traces of ca 15 narrow tracheids emitted in alternating helices, probably penetrating microphyllous leaves