Acta Palaeobot. Suppl. 2: 633–641, 1999 — Proceedings 5th EPPC THE TAXONOMY OF FAGUS IN WESTERN EURASIA AND THE ANCESTORS OF FAGUS SYLVATICA S.L. THOMAS DENK Swedish Museum of Natural History, Department of Palaeobotany, Box 50007, 10405 Stockholm; e-mail: thomas.denk@nrm.se ABSTRACT. A considerable amount of variability within extant populations of Fagus sylvatica is caused by modification. In addition, morphoclines occur from W to the E as well as in a mosaic-like pattern. The European F. sylvatica ssp. sylvatica turns out to be morpho- logically homogeneous while the SW Asian F. sylvatica ssp. orientalis is more heterogeneous. N Iranian populations of ssp. orientalis show strong similarities to F. grandifolia ssp. caroliniana in S Georgia and Florida. Ancestors similar to F. sylvatica already existed in the Pliocene (Frankfurt, Willershausen, Berga) and Upper Miocene (Iceland, Rus- sia). The extant W-E gradient between ssp. sylvatica and ssp. orientalis seems not to have existed in the same way during the Pliocene. Upper Miocene beeches of Iceland (F. antipofii, leaves and cupules) as well as the Mediterranean F. gussonii resemble extant F. sylvatica ssp. orientalis of N Turkey and Transcaucasia. The genus Fagus can be characterised by an initial reticulate evolutionary phase, which resulted in morphological parallelisms. KEY WORDS: Fagus, W Eurasia, reticulate evolution, parallelism INTRODUCTION Though the genus Fagus is comparatively small, con- cepts on the species numbers within Fagus are contro- versial (Table 1). The present state-of-the-art is to treat European and W Asiatic beech taxa as only one species, Fagus sylvatica, the Common beech, which consists of two subspecies: ssp. sylvatica and ssp. orientalis (Greuter & Burdet 1981). The Moesian beech of the Bal- kans is supposed to be a hybrid between the latter two. Important characters to distinguish the European beech from the oriental beech are the appendages of the cu- pules and the number of secondaries. Both, ssp. sylvatica and ssp. orientalis are supposed to have entire leaf mar- gins. Shen (1992) questioned the present concept and re- established Hohenacker’s beech, F. sylvatica ssp. hohen- ackeriana, which has been described by Palibin (1908) for Caucasia and Iran. Based on the current taxonomic concept of extant beeches the derivation of contempo- rary W Eurasiatic beech types from pre-Quaternary taxa turns out to be unclear (Kvaèek & Walther 1991). Wal- ther (1994) assumed European Tertiary beeches to have become extinct at the end of the Tertiary and according to this interpretation Fagus sylvatica should be of post- glacial origin. The present paper is part of a study with the aim of critically revising extant taxa of Fagus in western Eurasia with emphasis on the phenotypic vari- ability of leaves and cupules. Extensive field studies in Europe, Turkey, Transcaucasia and Iran have been un- dertaken by the author. The collected material of Fagus has been analysed morphometrically. Based on these in- vestigations a number of Miocene and Pliocene fossil species and their relations to extant taxa were reevalu- ated. TAXONOMY OF EXTANT FAGUS IN WESTERN EURASIA A considerable amount of morphological variability within Fagus is caused by modifications, which means the phenotypic response of the genus to particular envi- ronmental conditions. Characters, which are strongly in- fluenced by modifications are the texture of leaves (sun leaves vs. shade leaves) the leaf margin (entire vs. den- tate), size of the leaf and number of secondaries as well as the degree of pubescence. Naturally, modifications are the ”taxonomic noise” we have to deal with and must not be mistaken for specific characters (see Denk 1999a, b). In addition, a clinal transition of characters occurs from W Europe to N Iran (Table 2). According to my results most of the Bulgarian beech populations (Fagus moesi- aca) fit well into the morphological range of F. sylvatica ssp. sylvatica. A hiatus only exists in the easternmost Bulgaria, where scattered populations bearing leaf-like, stalked appendages are to be found (eastern Stara Plan- ina). Prominent leaf-like appendages get frequent in N Turkey but are less common in Georgia and north Iran. A second hiatus can be observed between Transcaucasian