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

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

Discovery

The first specimens belonging to Pentoxylales were reported by

Birbal Sahni Birbal Sahni Royal Society, FRS (14 November 1891 – 10 April 1949) was an Indian paleobotanist who studied the fossils of the Indian subcontinent. He also took an interest in geology and archaeology. He founded what is now the Birbal Sahni Ins ...

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 dom ...

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 Form classification is the classification of organisms based on their morphology (biology), morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncer ...

Pentoxylon 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 t ...

'', 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 Epidermis (botany), dermal nor Vascular tissue, vascular. It can be divided into three types based on the nature of the cell walls. # Parenchyma cells have thin primary walls and ...

Leaves

Leaves of Pentoxylales are of the strap shaped '' Taenopteris'' morphotype shared with other groups of seed plants, while leaves that preserve the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

are referred to the morphogenus '' Nipaniophyllum.'' The leaves are up to 20 centimetres long, and have a prominent

midrib This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

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, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

up to 6 mm long. The pollen is

monosulcate Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

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 fe ...

. 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 In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particula ...

, 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 mechani ...

. 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 A liana is a long- stemmed, woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the canopy in search of direct sunlight. The word ''liana'' does not refer to a ta ...

-like anatomy has also led to suggestions of a habit similar to that of

brambles A bramble is any rough, tangled, prickly shrub, usually in the genus ''Rubus'', which grows blackberries, raspberries, or dewberries. "Bramble" is also used to describe other prickly shrubs, such as roses (''Rosa'' species). The fruits inclu ...

.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