Zygopterid ferns †

Ecology & Form

Stem

• Stems that were mostly herbaceous with  small amounts of wood (secondary growth)

• Most plants were small, but some reached 3 m in height 

• Main axis is protostele (radial) 

• Secondary growth comes from a unifacial (one-sided) cambium, unlike woody (lignophyte) plants

  • Only wood (secondary xylem) produced; not secondary phloem [this is analogous to the unifacial cambium of the lepidodendrids)

  • Secondary growth only in periclinal divisions (adding girth)

  • No anticlinal division observed which would add more cambial initials as stem increases in girth

• Periderm has been observed in the rhizome of Zygopteris (Scott 1912; Phillips and Galtier 2005)

Leaf

Morphology

• The rachis is radially symmetrical in x.s., unlike the bilaterally symmetrical arrangement in true ferns 

  • Referred to as a phyllophore (Phillips 1974)

• Etapteroid type: three-dimensional fronds that were quadriserate  (=pinna in four ranks or rows); open peripheral loops

• Clepsydroid type: two-ranks of primary pinna, similar to modern ferns, with an hour-glass, H-shaped (clepsydroid) anatomy; closed peripheral loops

• The pinnae are small and planated

• Ultimate pinnae have dichotomizing veins.

Anatomy

• Rachis trace can be C-, E-, H-, I-, X, or Y-shaped

• Phyllophore exhibits bipolar primary strands, sometimes with peripheral loops

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Reproduction

• • Fertile fronds have clusters of sporangia that replace pinnules

  • Sporangia are elongate and produced in large clusters on abaxial surface

Diversity

Alloiopteris †

• Potonié 1897

• A. arkansana; A. plumosaeformis; A. winslovi

Asterochlaena †

• Corda 1845 

• Permian

• Stem, 8cm in width, with deeply-lobed primary xylem and shoot-born roots and phyllophores with clepsydroid anatomy

• Leaf traces arise from the lobes to become hourglass-shaped

Asterochlaenopsis kirgisica †

• Sahni 1930

• Permian of Siberia

• Stem with cylindrical stele and a mixed pith

Austroclepsis australis  †

• Sahni 1932

• Tournaisian of Australia

• Tree fern with 30 cm wide "false stem" with numerous stems with leaves and roots

Biscalitheca †

• Mamay 1957

• B. kansana; B. musata; B. suzanneana

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Brittsia †

Clepsydropsis †

• Unger 1856

• Small, C-shaped pinna traces and peripheral loops with little parenchyma (Phillips & Galtier 2005)

• C. bertrandi; C. campbelli; C. chaneyi; C. leclercqii; C. titan

Corynepteris †

Dernbachia brasiliensis †

• Rössler & Galtier 2002

• Permian of Brazil

• Small tree fern with 6-18 cm in diameter with large actinostele surrounded by a narrow cortex extending into leaf bases and root mantle

• Leaf traces depart stele as oval traces and become π-shaped; leaves arrange in pseudowhorls

Diplolabis †

Ellesmeris † 

• Hill et al. 1997

• Early Late Devonian (Frasnian) of southern Ellesmere Island, Canadian Arctic Archipelago.

• Plant occurs in an Archaeopteris-dominated flora preserved in the Nordstrand Point Formation (Mid-Late Frasnian) near Bird Fjord.

• The plant has a pinnate vegetative system with three branch orders and laminate sphenopteroid pinnules.

• Primary pinnae usually diverge from the main axis in distichous pairs (quadriseriate), but can depart singly (biseriate).

• Each primary pinna bears a basal catadromic aphlebia. 

• Anatomically, the plant exhibits a mesarch bipolar protostele that is ribbon- to clepsydropsoid-shaped in the main axis. 

• Primary pinna traces are also initially bipolar and crescent-shaped, but may become four-ribbed before dividing into a pair of bipolar traces.

Nemejcopteris †

Protoclepsydropsis †

Symplocopteris †

Yulebacaulis †

Zygopteris †