The genus was first erected byLindley andHutton in "The fossil flora of Great Britain",[2] based on material ofCtenis falcata from theJurassic ofYorkshire. This species was latersynonymized withCycadites sulcicaulis, leading to the new combinationCtenis sulcicaulis[3]. Later,Seward,[4]Florin, andHarris[5] added details of the cuticle to the diagnosis of the genus.
Due to the leaves ofCtenis possessing characters unknown in any living cycad,Ctenis is thought to belong to an extinct lineage distinct from modern cycads, with a 2023 analysis finding that the genus wasparaphyletic with respect toDioonopsis andPterostoma, with this group suggested to be the sister group to Cycadaceae, from which they split in thePermian period.[6]
The leaves ofCtenis are once pinnate, and the pinnae have multiple parallel veins that often anastomosize (i.e. fuse together).[7][8] The cuticle ofCtenis has stomata with guard cells arranged in a random fashion, and the stomatal apparatus has often a cuticular ring surrounding the stomatal pit. The cuticular surface is usually striate.
ThoughCtenis-like leaves are known from theLate PermianUmm Irna Formation ofJordan,[9]Ctenis becomes more common from theLate Triassic onwards. In theJurassic, manyCtenis species are retrieved from Europe, North America, and Asia.[10][7] In theEarly Cretaceous,Ctenis is still found in Europe (i.e. in theWealden[11]) and Asia,[12] but from the Late Cretaceous it seems to retreat to more Northern Latitudes in the Siberian region[13] and North America[14] and Southern latitudes in Australia. The last members of this genus are found in theEocene of North America.[8]
Little is known about the ecology of theCtenis-producing plants. However, in theBig Cedar Ridge locality inWyoming (Campanian),Ctenis is found in the fern wetland together with ferns from theDipteridaceae,Gleicheniaceae, andMatoniaceae.[15] This suggests that at least some members of the genus inhabited wet environments with peaty soils.
