Sagenopteris

Sagenopteris is a form genus of leaves belonging to the extinct seed plant order Caytoniales, spanning from the Middle Triassic to Late Cretaceous.

Description

Sagenopteris has two pairs of palmately arranged leaflets with anastomosing venation and a prominent midrib, which are all attached to the apex of a petiole. Mature leaves are generally lanceolate to oblanceolate, the edges are generally entire, slightly undulating, and occasionally lobed or dentate, the cuticle is somewhat thick, and the stomata are only present on the underside of the leaflets. According to Xu et al. 2024, the stomata are characterised by "guard cells with a flat surface and a sunken region around the aperture; guard cells typically surrounded by a single ring of weakly modified neighbouring cells in an anomocytic arrangement".
Different organs attributed to the same original plant can be reconstructed from co-occurrence at the same locality and from similarities in the stomatal apparatus and other anatomical peculiarities of fossilized cuticles.

Sagenopteris phillipsii may have been produced by the same plant as Caytonia nathorstii and Caytonanthus arberi.

Species

The following species have been described:

Sagenopteris colpodes
Sagenopteris elliptica
Sagenopteris mclearni
Sagenopteris nilssoniana
Sagenopteris oregonensis
Sagenopteris phillipsii
Sagenopteris trapialensis
Sagenopteris variabilis
Sagenopteris williamsii

In a 2024 review, only 5 species, Sagenopteris acuminata, S. colpodes, S. hallei, S. phillipsii and S. pualensis were considered valid.

Distribution

Fossils of Sagenopteris have been registered in:
;Triassic
Argentina, China, Germany, Greenland, Italy, Japan, Kyrgyzstan, the Russian Federation, Sweden, Tajikistan, Ukraine, United States.
;Jurassic
Afghanistan, Antarctica, Argentina, Azerbaijan, Belarus, Canada, China, Colombia, Georgia, Germany, Greenland, India, Iran, Italy, Japan, Kazakhstan, Kyrgyzstan, Mexico, Peru, Poland, Romania, the Russian Federation, Tajikistan, Turkmenistan, Ukraine, the United Kingdom, United States, and Uzbekistan.
;Cretaceous
Spain, Belgium, Canada, Greenland, the Russian Federation, and the United States.