For the Alaskan specimens morphotype 'names' are often used when assignment to a known genus and species is problematical. They are informal, but useful, ways or refering to leaf types and are based on a system that immediately conveys something about the leaf form.
The unique numerical form identifiers are prefixed by alphabetic characters which indicate in broad terms the main features of the leaf architecture. Many of the characters in Hickey's leaf classification scheme (1973, 1979) are correlated even in Cretaceous leaf forms. For example many leaves possess entire margins, camptodrome venation and intersecondary veins; all features found associated in extant members of the Magnoliidae. The Cretaceous angiospermous forms have therefore been partitioned into artificial groups that exhibit the same consistent character associations. The codes used to identify these groups are derived from the architectural features they exhibit and in some cases modern subclass names. The modern subclass names (broadly based on Takhtajan, 1969), are used not because of any supposed phylogenetic relationship, but merely because the general character combinations are readily comprehended from familiarity with the extant leaf forms.
Parentheses enclosing part or all of the prefix indicate uncertainty. U indicates the affinities are unknown.
If at any time it should be considered necessary to change the group to which a form is assigned it would be a simple matter to change the prefix while retaining the unique form number. A change in this form number need only be made when the specimens comprising a form are all dispersed to other forms and the original form is abandoned.
In the Smiley collection a different system is used where an informal label is given to a specimen such as 'Conifer 18' or 'Conites 4'. These names were given by Smiley when he created his biostratigraphic scheme. We have retained these for historical continuity. Sometimes Smiley used a genus name as a temporary lable instead. Again, we have retained these. Note, however, that sometimes Smiley's genus names differ from those assigned by us with the benefit of direct access to comparative Russian specimens.