This is a clade that includes the clubmosses (lycopsida) and an extinct sister group, the zosterophylls. This group is united by features based on how the xylem matures in the stems, and how the sporangia are arranged on the stems.
Ecology & Form
Sporophyte (spore-bearing) phase
Exarch maturation: xylem matures from the periphery toward the center of stem
This is the synapomorphy for this clade
Isotomous and anisotomous branching is exhibited
Zosterophyllophytes lack leaves, but may exhibit enations
Lycopods exhibit lycophylls or microphylls
Present in advanced forms
Rhizophore (root-like stem) and roots found in lycopods
Halleophyton zhichangense †
Pragian from the Posongchong Formation of eastern Yunnan, China
The plant had leafy aerial stems. The leaf bases completely covered the stems forming rhomboidal to hexagonal patterns, except where spore-forming organs or sporangia were present where the leaves thinned out somewhat.
The tapered undivided leaves curved inwards and appear to have had a central vein.
The sporangia were mixed with leaves and were more-or-less circular in outline, consisting of two valves that split to release the spores.
Halleophyton has similarities with Drepanophycus, but a lack of detailed knowledge of some features of that genus persuaded Li and Edwards to create a new genus for their specimens.
Although considered to be related to the lycophytes, the exact placement of the genus was left open by its authors. Hao and Xue in 2013 listed the genus as a lycopsid.
Ornicephalum sichuanense †
Early Devonian of Sichuan, China
Plant with smooth stems terminating in lax strobili composed of bivalved sporangia inserted helically and supported by long distally curved stalks
Sporangia consist of two unequal valves, the smaller being adaxial and separated from the larger abaxial valve by an almost transverse dehiscence line
Stalk merges with the outer surface of the abaxial valve such that no junction is visible
Yanmenia longa †
Early Devonian, Sichuan Province, China
Herbaceous leafy stems with distal branching isotomous or lateral in opposite pairs
Simple entire persistent leaves with decurrent broad bases and bifacial laminae, almost circular to elliptical in face view. Laminae directed distally
Leaves attached to all sides of stem in a low helix, 6 or rarely 8 per gyre.