''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 are among the most common Mesozoic seed plants ...

. 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 grc, ῥάχις [], "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 c ...

of the leaf. ''Nilssoniopteris''-like leaves are distinguished by their syndetocheilic stomata, 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 with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or f ...

affinities), or '' Taeniopteris'' if the cuticle is not preserved.

References

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