Pentoxylales is an extinct order of seed plants known from the Jurassic and Early Cretaceous of East Gondwana.

Discovery

The first specimens belonging to Pentoxylales were reported by Birbal Sahni in 1948 from Jurassic-Cretaceous strata of the

Rajmahal Hills The Rajmahal Hills are located in the Santhal Pargana division of Jharkhand, India. They were located on the northern margin of the Gondwana supercontinent, and its hills are today inhabited by the Sauria Paharia people whilst its valleys are d ...

of northeastern India. Remains have subsequently been reported from New Zealand, Australia and Antarctica. The oldest records of the group date to the Upper Jurassic, though there are unconfirmed Early Jurassic records.

Morphology

Stem

The stem of Pentoxylales, referred to by the morphogenus '' Pentoxylon'', consists of 5 or 6 wedge shaped segments embedded within thin walled

ground tissue The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. # Parenchyma cells have thin primary walls and usually remain alive after they beco ...

Leaves

Leaves of Pentoxylales are of the strap shaped '' Taenopteris'' morphotype shared with other groups of seed plants, while leaves that preserve the cuticle are referred to the morphogenus '' Nipaniophyllum.'' The leaves are up to 20 centimetres long, and have a prominent midrib.

Pollen organs

The pollen organs of Pentoxylales, referred to the morphogenus ''Sahnia'', consist of microsporophylls arranged in tight spirals around or on a cylindrical or dome-shaped receptacle. The base of the pollen organs are surrounded by

bracts In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the An ...

up to 6 mm long. The pollen is monosulcate and approximately 25 µm long.

Seed bearing organs

Seed bearing organs of Pentoxylales, dubbed '' Carnoconites'', which have a central axis or peduncle, which branches into numerous structures that end with an

ovule 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 ...

. The morphology has variously been described as infructescences,

seed cones A conifer cone (in formal botanical usage: strobilus, plural strobili) is a seed-bearing organ on gymnosperm plants. It is usually woody, ovoid to globular, including scales and bracts arranged around a central axis, especially in conifers an ...

, seed-bearing fruits, or female

flowers A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...

. The seeds are apparently sessile.

Whole plant reconstruction

The

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

of Pentoxylales is uncertain. They have been suggested to have been small

trees In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are u ...

. Their liana-like anatomy has also led to suggestions of a habit similar to that of brambles.Howe, J., & Cantrill, D. J. (2001). Palaeoecology and taxonomy of Pentoxylales from the Albian of Antarctica. ''Cretaceous Research, 22'', 779–793.

Phylogenetics

The affinities of Pentoxylales remain obscure, phylogenetic analyses have proposed various affinities with other seed plants groups, including glossopterids and

Bennettitales Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales are among the most common Mesozoic seed plants ...

, but evidence for this is inconclusive, and they cannot be definitively linked with any other seed plant group.

References

{{Taxonbar, from=Q35135259 Prehistoric plant orders Mesozoic plants Prehistoric gymnosperms