''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
The Hettangian is the earliest age and lowest stage of the Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (My ...
of
Scania
Scania, also known by its native name of Skåne (, ), is the southernmost of the historical provinces of Sweden, provinces (''landskap'') of Sweden. Located in the south tip of the geographical region of Götaland, the province is roughly conte ...
. 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
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 ...
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' (