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
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 †
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.
