''Nilssonia'' is a genus of fossil foliage traditionally assigned to the Cycadophyta either in
Cycadales
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 ...
or their own order Nilssoniales, though the relationships of this genus with the Cycadales have been put into question on chemical grounds.
Taxonomy
The genus was erected by
Brongniart under the name ''Nilsonia'' based on material from the
Hettangian of
Scania
Scania, also known by its native name of Skåne (, ), is the southernmost of the historical provinces (''landskap'') of Sweden. Located in the south tip of the geographical region of Götaland, the province is roughly conterminous with Skåne ...
. The spelling of the name (a dedication to
Sven Nilsson) was later corrected to ''Nilssonia''. The diagnosis of the genus, initially based on the pinnate ''Nilssonia brevis'', was later amended to include entire-margined and irregularly segmented species as well as information on the cuticle.
Description
''Nilssonia'' leaves can have
entire margins, irregularly dissected margins or clearly divided
leaflets. The lamina or the leaflets are attached to the
midrib or
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 ...
on the 'upper' (