Cheirolepidiaceae

Cheirolepidiaceae (also spelled Cheirolepidaceae) is an extinct family of conifers. They first appeared in the Triassic, and were widespread during most of the Mesozoic era. They are united by the possession of a distinctive pollen type assigned to the form genus Classopollis. The name Frenelopsidaceae (as a separate family) or "frenelopsids" has been used for a group of Cheirolepidiaceae with jointed stems, thick internode cuticles, sheathing leaf bases and reduced free leaf tips. The leaf morphology has been noted as being similar to that of halophyte Salicornia. Several members of the family appear to have been adapted for semi-arid and coastal settings, with a high tolerance of saline conditions. Cheirolepidiaceae disappeared from most regions of the world during the Cenomanian-Turonian stages of the Late Cretaceous, but reappeared in South America during the Maastrichtian, the final stage of the Cretaceous, increasing in abundance after the K-Pg extinction and being a prominent part of the regional flora during the Paleocene, before going extinct. The habit of cheirolepidaceous confers is likely to have varied widely, from large trees (some with trunks over 3 metres thick at their base) to shrubs. Their architecture is poorly known, though some are thought to have had decurrent spreading crowns, while others had conical crowns. Many seem to have plagiotropic lateral branches that developed in whorls. The relationships of Cheirolepidiaceae to other conifers are uncertain. A close relationship with Araucariaceae and Podocarpaceae has been proposed, based on the similarities of their reproductive structures. At least some species of Cheirolepidiaceae have been suggested to have been pollinated by insects, due to the construction of the reproductive organs and the fact that insects have been found associated with Classopolis pollen grains. The family name Hirmeriellaceae is a junior synonym of Cheirolepidiaceae.