''Nilssoniopteris'' is an extinct form genus of leaves belonging to the

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 were amongst the most common seed plants of th ...

. Leaves are slender and often entire-margined (smooth-edged), though some species have dissected leaves with numerous small segments extending down to the

rachis In biology, a rachis (from the [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachi ...

of the leaf. ''Nilssoniopteris''-like leaves are distinguished by their syndetocheilic

stomata In botany, a stoma (: stomata, from Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spa ...

, indicating bennettitalean affinities. Similar "taeniopterid" leaves are placed in the genus '' Nilssonia'' if their stomata are instead haplocheilic (indicating

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...

affinities), or ''

Taeniopteris ''Taeniopteris'' is an Extinction, extinct form genus of Mesozoic vascular plant leaves, perhaps representing those of Cycad, cycads, Bennettitales, bennettitaleans, or Marattiales, marattialean ferns. The form genus is almost certainly a polyphy ...

'' if 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 ...

is not preserved. Leaves of ''Nilssoniopteris vittata'' from the Middle Jurassic of England are associated with bisexual '' Williamsoniella'' reproductive structures.

References

Prehistoric plant genera Bennettitales Permian plants Triassic plants Jurassic plants Cretaceous plants Prehistoric plants of North America {{Cretaceous-plant-stub