Sphenophylls †

Woody, horsetail-like plants

The Sphenophyllophytes are an extinct group of spore-bearing, vascular plants, deriving their name from the wedge-shaped appearance of their leaves (spheno-phyll). They are a controversial group with loose connections to horsetails or ferns, or maybe lycophytes. They were abundant in Pennsylvanian, exhibiting a creeping or climbing habit in over-bank flood plain and lake edge habitats. The sphenophylls may have been under-story shrubs (less then 1 meter) in the arborescent lycopsid forests of the same time period.

Ecology and Form

Creeping or climbing habit
Found in over-bank flood plain and lake edge habitats

Stems

Morphology

Compressions exhibit distinct node/internode arrangement like horsetails
Stems up to 2 cm in diameter
Many orders of branching

Anatomy

Trilobed protostele
- Exarch maturation (similar to lycophytes)
- Mesarch maturation found in some (similar to euphyllophytes)
Some woody tissues
- Unifacial (maybe bifacial) cambium similar to lycopsids
- Cambium was determinate, with limited woody growth
- Secondary growth only in periclinal divisions; not anticlinal to add more cambial initials as stem increases in girth

Leaves

Compression/impression fossils (e.g Sphenophyllum)
Whorled arrangement
Wedge-shaped leaves ("spheno-phyll")
- Origin unknown: microphylls, megaphylls, independent origin?

Reproductive Structures

Sporangia aggregated into loose cones (e.g. Bowmanites)
Sporangia on modified leaves (sporophylls), unlike horsetails
- Sporophyll on a stalk that recurves toward cone axis
Homosporous

Classification

└Sphenophyllales †

Geologic Age

Devonian-Triassic

Diversity

Bowmanites †

Permineralized, spore-bearing cones
Pennsylvanian of USA, Belgium, and UK
B. dawsonii (Taylor 1969, 1970)
B. moorei (Mamay 1959)

Cheirostrobus †

Above: Compression of Bowmanites

Eviostachya †

Problematic Late Devonian cone

Gondwanophyton †

Above: Reconstruction of Eviostachya

Above: Reconstruction of Gondwanophyton

Hamatophyton verticillatum †

Li et al. 1995; Wang et al. 2006
Late Devonian of China
Pseudomonopodial with axial trichomes or spines and nodal whorls of sterile leaves
Leaves are dimorphic and sometimes contain trichomes or spines
When mature, primary xylem is exarch and the secondary xylem lacks parenchyma

Above: Compression fossils of Hamatophyton

Lilpopia †

Conert and Schaarschmidt 1970
Mostly found in Karniowice area, Poland
L. polonica
L. raciborskii
L. crockensis

Peltastrobus †

Cone with sporangium that bore monolete spores

Sphenophyllum †

Parasphenophyllum †

Paratrizygia †

Rotafolia songziensis †

Wang et al. 2005; Wang et al. 2006
Late Devonian of China
Permineralized fertile stems and branches

Sentistrobus †

Trizygia †

Above: Peltastrobus

Above: Reconstruction of Sphenophyllum

Xihuphyllum †

Huang et al. 2016
Upper Devonian Wutong Formation of Zhejiang Province, China
Plant characterized by a hierarchical branching pattern, with robust nodose stems up to 42.5 mm wide and two orders of lateral branches.
Internode width of stems and first-order branches are correlated with the internode length.
Leaves, cuneate, broadly cuneate, or spatulate in shape and highly variable in size, are arranged in whorls at the nodes of stems and branches.
- The leaves reach over 80 mm in length and > 3000 mm2 in area, an unusually large size for Paleozoic sphenopsids
- Xihuphyllum is reconstructed as having a stature 2–3 m in height, and represents an early, large-bodied member within the extinct Sphenophyllales.

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