Lycophytes

Ecology & Form

Sporophyte (spore-bearing) phase

Stems

• 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

Leaves

• Zosterophyllophytes lack leaves, but may exhibit enations

• Lycopods exhibit lycophylls or microphylls

Roots

• Present in advanced forms

• Rhizophore (root-like stem) and roots found in lycopods

Reproductive Structures

• Sporangia are lateral along stem (not terminal as in rhyniophytes or cooksonioids)

  • Kidney-shaped (reniform) in shape

• Sporangia associated with the adaxial side of a leaf (sporophyll) in lycopods

Halleophyton zhichangense †

• Li & Edwards 1997

• 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.