Callistophytaceae

Callistophytaceae Temporal range: Carboniferous–Permian PreЄ Є O S D C P T J K Pg N
Reconstruction of the plant Callospermarion pusillum (permineralized ovules), Idanothekion callistophytoides (pollen organ), Dicksonites pluckenetii (leaves), Callistophyton poroxyloides (stem), and Vesicaspora shaubergeri (pollen) from the Pennsylvanian Calhoun Formation of Berryville, Illinois.
Scientific classification
Kingdom:	Plantae
Division:	†Pteridospermatophyta
Order:	†Callistophytales
Family:	†Callistophytaceae
Genera
Callospermarion ovule Idanothekion pollen organ Dicksonites leaves Mariopteris leaves Callistophyton permineralized wood Vesicaspora pollen

The Callistophytaceae was a family of seed ferns (pteridosperms) from the Carboniferous and Permian periods. They first appeared in late Middle Pennsylvanian (Moscovian) times, 306.5–311.7 million years ago (Ma) in the tropical coal forests of Euramerica, and became an important component of Late Pennsylvanian (Kasimovian-Gzhelian; 299.0–306.5 Ma) vegetation of clastic soils and some peat soils. The best known callistophyte was documented from Late Pennsylvanian coal ball petrifactions in North America.

The relatively slender stems (fossil genus Callistophyton) had a eustele with a well-developed zone of secondary wood, and unlike most (but not all) other Palaeozoic pteridosperms, showed axillary branching. These characters strongly point to its having been a scrambling or climbing plant. A characteristic feature of the stems is the presence in the cortex of spherical secretory structures. Similar structures have also been found in associated ovules, pollen-organs and foliage, and were one of the main lines of evidence on which the reconstruction of the plant was based (compare with similar evidence used to reconstruct the Lyginopteris-bearing fossil plant).

The small ovules (fossil genus Callospermarion) with the characteristic secretory structures have an integument that was only fused to the nucellus in the basal part of the ovules and so superficially resemble medullosalean ovules. Unlike the Medullosales, the ovules appear to be bilaterally symmetrical, although details of the vasculature suggest they were in fact evolved from plants with radially symmetrical ovules. The apical part of the nucellus has a lagenostome-like projection, which breaks down to form the pollen chamber. The full ontogeny of these ovules has been worked out in some detail and seems to be essentially similar to that seen in modern-day gymnosperms, including the use of a pollen drop to help capture and draw the pollen into the pollen chamber and a pollen tube to deliver the generative nucleus. The ovules were borne on the underside of pinnules that did not differ significantly in form from those of the purely vegetative fronds.