The Callistophytaceae was a family of seed

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except ...

s (

pteridosperms The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") is a polyphyletic group of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus ''Elkinsia'' of the late Devonia ...

) from the Carboniferous and

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

periods. They first appeared in late Middle

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the International Commission on Stratigraphy, ICS geologic timesca ...

(Moscovian) times, 306.5–311.7 million years ago ( Ma) in the tropical

coal forest Coal forests were the vast swathes of wetlands that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times.Cleal, C. J. & Thomas, B. A. (2005). "Palaeozoic tropical rainforests and their e ...

s of

Euramerica Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

, and became an important component of Late Pennsylvanian (Kasimovian-Gzhelian; 299.0–306.5 Ma) vegetation of

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rock ...

soils and some peat soils. The best known callistophyte was documented from Late Pennsylvanian

coal ball A coal ball is a type of concretion, varying in shape from an imperfect sphere to a flat-lying, irregular slab. Coal balls were formed in Carboniferous Period swamps and mires, when peat was prevented from being turned into coal by the high am ...

petrifactions in North America.Rothwell, G. W. (1981). "The Callistophytales (Pteridospermopsida). Reproductively sophisticated gymnosperms." ''Review of Palaeobotany and Palynology'', 32: 103-121.

Description

Stems

The relatively slender stems (fossil genus ''Callistophyton'') had a

eustele In a vascular plant, the stele is the central part of the root or stem containing the tissues derived from the procambium. These include vascular tissue, in some cases ground tissue (pith) and a pericycle, which, if present, defines the outermost bo ...

with a well-developed zone of secondary wood, and unlike most (but not all)Hamer, J. J. & Rothwell, G. W. (1988). The vegetative structure of ''Medullosa endocentrica'' (Pteridospermopsida). ''Canadian Journal of Botany'', 66: 375-387. other Palaeozoic pteridosperms, showed axillary branching.Rothwell, G. W. (1975). "The Callistophytaceae (Pteridospermopsida): I Vegetative structures." ''Palaeontographica, Abteilung B'', 151: 171-196. 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).

Ovules

The small

ovules In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the '' integument'', forming its outer layer, the '' nucellus'' (or remnant of the megasporangium), and the ...

(fossil genus ''Callospermarion'') with the characteristic secretory structures have an

integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind. Etymology The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...

that was only fused to the

nucellus In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the '' integument'', forming its outer layer, the '' nucellus'' (or remnant of the megasporangium), and the ...

in the

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

part of the

and so superficially resemble medullosalean

. Unlike the

Medullosales The Medullosales is an extinct order of pteridospermous seed plants characterised by large ovules with circular cross-section and a vascularised nucellus, complex pollen-organs, stems and rachides with a dissected stele, and frond-like leaves. ...

, the

appear to be bilaterally symmetrical, although details of the

vasculature The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

suggest they were in fact evolved from plants with radially symmetrical

. The

apical Apical means "pertaining to an apex". It may refer to: * Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features l ...

part of the

has a lagenostome-like projection, which breaks down to form the pollen chamber. The full

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

of these

has been worked out in some detail and seems to be essentially similar to that seen in modern-day

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s, 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.Rothwell, G. W. (1980). "The Callistophytaceae (Pteridospermopsida): II Reproductive features." ''Palaeontographica, Abteilung B'', 173: 85-106. The ovules were borne on the underside of pinnules that did not differ significantly in form from those of the purely vegetative fronds.

Synangia

The pollen-producing organs (fossil genus ''Idanothekion'') consisted of small, radially symmetrical synangia, with each pollen-sac having a longitudinal dehisence structure.Millay, M. A. & Eggert, D. A. (1970). ''Idanothekion'' gen. n., a synangiate pollen organ with saccate pollen from the Middle Pennsylvanian of Illinois. ''American Journal of Botany'', 57: 50-61. Like the ovules, the synangia were attached to the underside of pinnules that did not differ significantly in form from those of the purely vegetative fronds, and so can give a superficially similarity to fertile fern fronds. Unlike ferns, however, these pollen-organs produced monolete, bisaccate pollen (fossil genus ''Vesicaspora'') bearing some similarity to the pollen of many conifers.

Foliage

The foliage, which is the part of these plants most widely-found as

macrofossil Macrofossils, also known as megafossils, are preserved organic remains large enough to be visible without a microscope. The term ''macrofossil'' stands in opposition to the term microfossil. Microfossils, by contrast, require substantial magnific ...

s, consists of fronds with a basal dichotomy of the main rachis, each branch producing pinnately divided segments, but with no pinnae attached below the dichotomy.Galtier, J. & Béthoux, O. (2002). Morphology and growth habit of ''Dicksonites pluckenetii'' from the Upper Carboniferous of Graissessac (France). ''Geobios'', 35: 525-535. Such fronds, when found as adpressions, are known as ''Dicksonites''. The pinnules tend to be tongue-shaped or somewhat lobed, and can closely resemble pinnules of

Lyginopteridales The Lyginopteridales were the archetypal pteridosperms: They were the first plant fossils to be described as pteridosperms and, thus, the group on which the concept of pteridosperms was first developed;Oliver, F. W. & Scott, D. H. (1904). "On th ...

fronds such as ''Mariopteris''. Distinguishing the fronds of these two orders of pteridosperms can in fact be very difficult unless the pinnules are fertile, although generally the pinnule lamina of ''Dicksonites'' fronds tend to be somewhat vaulted, whereas ''Mariopteris'' pinnules are usually flatter.

Distribution

Occasional ''Vesicaspora'' pollen grains and fragments of ''Dicksonites''-like fronds occur in early Moscovian (middle Westphalian) strata, especially in intra-montane basins. However, callistophyte foliage and pollen suddenly become relatively widespread and abundant in Euramerican floras in late Moscovian (late Asturian) floras. This increase in callistophyte abundance is one of the indexes to the base of what is called the ''Dicksonites plueckenetii'' Subzone,Cleal, C. J. & Thomas, B. A. (1994). Plant fossils of the British Coal Measures. Palaeontological Association, London. which marks a significant phase in the continent-wide changes to the wetland ("coal swamp") vegetation that took place in late Moscovian times in response to a combination of tectonics-induced landscape changes and climate change.Cleal, C. J. & Thomas, B. A. (2005). Palaeozoic tropical rainforests and their effect on global climates: is the past the key to the present? ''Geobiology'', 3: 13-31.. The increase in abundance of the callistophytes coincided with a decline in abundance and diversity of the Lyginopteridales, which occupied very similar ecological niches and were very similar in general habit. It seems possible, therefore, that the reproductively more sophisticated callistophytes were able to out-compete and replace the Lyginopteridales. The Callistophytaceae flourished in Euramerica through Late Pennsylvanian times, eventually becoming extinct as this part of Pangaea became arid at the start of Permian times. They extend through the Permian of China and include anatomically preserved ovules of ''Callospermarion'', vegetative foliage of ''Emplecopteris triagularis'', male organs of Norinotheca and ovulate fronds of Norinosperma, and stems of Calistophyton. Callistophytales appear to be victims of the Permo-Triassic extinction event in 'Cathaysia'.Seyfullah, L. J. and Hilton, J. (2011). Callistophytalean pteridosperms from the Permian floras of China. Palaeontology 54: 287–302.

References

{{Taxonbar, from=Q5022813 Pteridospermatophyta Carboniferous plants Permian plants Prehistoric plant families Carboniferous first appearances Permian extinctions