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Sphenostrobus thompsonii
Sphenostrobus thompsonii Levittan, Bargh. Amer. J. Bot., 35(6): 353. 16 Jul 1948
- Name
- Sphenostrobus thompsonii
- Rank
- Species
- Generic Name
- [Genus] Sphenostrobus
- Authors (Pub.)
- Levittan E. D.
Barghoorn E. S.
- Publication
- Sphenostrobus thompsonii: a new genus of the Spenophyllales? [1948/7]
- Journal
- American Journal of Botany
- Volume
- 35
- Issue
- 6
- Page number
- 353
- Year
- 1948
- Fossil Status
- cones
- Stratigraphy
- Moscovian
- Strat. comment
- Des Moines Series
- Location
- D. Shuler Mine, Walnut Township, Dallas County, Iowa, USA
- Paleoregion
- Laurussia (Laurentia)
Data for Holotypus
- Repository
- Harvard University, Cambridge, Mass., USA
- Repository Number
- 46 peel sections: No. 50,001 to 50,046
- Diagnosis
- A small cone about 9 mm. in diameter and in excess of 15 mm. in length. The axis is about 1.25 mm. in diameter. The vascular cylinder is in the form of a tetrarch protostele, exarch in development and devoid of a pith. Secondary growth is absent. The protoxylem consists of a few strands of spiral or annular elements. Metaxylem tracheids exhibit scalariform or multi- seriate circular bordered pits. Sporophylls 16 per whorl, basally united to form a complete collar. Sporophylls thickened centrally in a radial direction, their laterally fused margins producing radiating interpedicellar grooves. Sporophylls with free tips, the laminae of which extend upward for two to three nodes, producing an intri- cate strobilus. Bases of the sporophylls inserted on the axis at an angle of 900. Sporophylls successively superposed. Sporangia are elongated sac-like structures about 2 mm. in length, 0.8 mm. in width and 1.6 mm. in height. There are 16 sporangia to a single whorl. Sporangia are borne sessile, and are attached by their inner ends; they alternate with the sporophylls and rest in the grooves of the subtending sporophyllar disc. The cone is apparently homosporous with spores averaging 95 ,u in diameter. Perisporium and spines absent. A net-like reticulum with minor folding characterizes the exine. Triradiate scars present.
