Where the specimen has been identified to a previously described form a formal Linnaean binomial is used. A Linnaean binomial consists, as the term 'binomial' suggests, of two parts: a genus name (e.g. Metasequoia) and a name that, in combination with the genus name, is unique to the species (e.g. Metasequoia occidentalis). This second name is called the species epithet. Sometimes when an epithet is not needed, such as when we want to refer to all species in a given genus, only a genus name will be given. Where we can identify a fossil to a genus but not to a particular species within that genus we use the genus name followed by 'sp.'. When a Linnaean binomial is first used in the text, or when it is part of a formal description, then an authority (the name of the author(s) who first described or emended the description) is added after the binomial.
In this catalogue formal binomial names are only given to those specimens that we can positively identify to a previously published species or genus. To have authority a formal name must have been published in a recognised scientific publication according to the rules laid down under the International Code of Nomeclature for algae, fungi and plants. This illustrated catalogue is not the place to erect new formal names so many of our specimens are given temporary or informal names until such as they are described formally. Our informal names follow several completely different systems from that designed by Linnaeus and are given morphotype descriptors usually consisting of letter and numbers.
Fossil specimens are inevitably only a shadow of the once living organism or plant part. Leaves may lack features critical to identification such as margin form, venation or cuticle characters so, inevitably, naming is imprecise. Imprecision is also a function of the variability that leaves display. For Cretaceous leaves this variability is often very large, in part caused by reticulate evolution. Many individual Cretaceous leaves display a mixture of characters that today do not occur together but are separated across two or more families. For this reason we do not attempt to assign genera to living families.
To reflect different levels of uncertainty in identification we use a set of qualifiers in this catalogue.
Ex gr. is the qualifier that indicates the lowest level of uncertainty. The term 'ex gr.' refers to 'ex gregor', which means 'from the herd' and is used when the specimen lacks some characters that were present in the type specimen associated with the formal name. This may be, for example, cuticle where cuticle characters were included in the description of the type specimen that forms the basis of the name but are not preserved in the specimen at hand.
Aff. This means that the specimen shows an affinity to a particular species. This means that the specimen is similar, but not identical, to the specimen (nomenclatural type) used as the basis for the name. It can be applied to both the genus name or the species epithet. When applied to the genus name it indicates a higher level of uncertainty than when used with the species epithet.
Cf. This means 'compare with' and indicates that our specimen shows only some of the features found in the figured type material. However we can find no other published material that is closer in from to our specimen.
? A question mark indicates that we are uncertain if our material really is assignable to this taxon but the name given is the best we can suggest.
Indet. This signifies that the material we have is either so incomplete that we cannot assign it to any described taxon or that the material is unique and requires a new name to be erected.