| The Annonaceae is a large, mainly tropical family of angiosperms with 129 genera and approximately 2150 species of trees, shrubs and lianes. Only Asimina triloba (L.) Dunal, the pawpaw, lives in truly temperate areas and it is restricted to eastern North America. Leaves of the Annonaceae are alternate, simple, entire-margined, pinnately-veined and estipulate. On the basis of gross morphology alone they can easily be confused with those of other magnolialean and related families. A comparative study of the epidermal anatomy of leaves of the Magnoliales, Illiciales, Laurales, Trochodendrales, Cercidiphyllales and Eupteleales with special emphasis on the Annonaceae was done in order to determine the taxonomic potential of epidermal characteristics in distinguishing leaves of the Annonaceae from those of the other families studied and in revealing phylogenetic relationships in the family. Reflected and transmitted light microscopy and scanning electron microscopy were used on 902 specimens representing 749 species of 207 genera of 52 families. The variation of epidermal characteristic and the selection of taxonomically valuable characteristics are discussed. Sixteen trichome types of the Annonaceae are described and their possible evolutionary derivation is presented. Two taxonomic keys demonstrating the value of epidermal analysis are included. One distinguishes leaves of the Annonaceae from those of the other families studied, and the other distinguishes genera within the family. The stability of major epidermal characteristics is demonstrated in a comparative study of stomatal development in the temperate species, Asimina triloba, and its tropical relatives. The generic status of Deeringothamnus Small is confirmed by epidermal analysis which revealed that the leaves of both species of Deeringothamnus are unique within the Annonaceae in that they are amphistomatic. The taxonomic affinities of one fossil leaf type from the Middle Eocene Claiborne Formation of western Tennessee and Kentucky are clarified on the basis of gross morphology, fine venation and epidermal analysis. The fossil leaf type has peltate-stellate scales and represents an extinct species of the modern annonaceous genus Duguetia St. Hil. |
