Acer aemilianum SORDELLI , 1896

Denk, Thomas, Sami, Marco, Teodoridis, Vasilis & Martinetto, Edoardo, 2022, The Late Early Pleistocene Flora Of Oriolo, Faenza (Italy): Assembly Of The Modern Forest Biome, Fossil Imprint 78 (1), pp. 217-262 : 240-244

Acer aemilianum SORDELLI, 1896

Text-fig. 13a, d–g

1896 Acer aemilianum SORDELLI , p. 156, pl. 30, fig. 8.

1988 Acer polymorphum SIEBOLD et ZUCC. pliocenica SAPORTA; Jorda et al., p. 54, pl. 1, figs 10–13.

M a t e r i a l. Oriolo MSF 645, 645-1, 660, 660-1, 661,

661-1.

D e s c r i p t i o n. Leaf, petiolate, petiole ca. 3 cm long, with widened proximal part, lamina up to 52 mm long, 71 mm wide, primary venation palmate, number of primary veins 7–9 (–11), number of lobes 7–9 (–11), lobe apex attenuate, secondary venation craspedodromous, margin finely serrate or double-serrate along the upper 2/3 or 4/5 of the free lobes.

R e m a r k s. The leaf remains from Oriolo clearly belong to A. aemilianum described by Sordelli (1896) from strata referred to as “Pliocene” (but possibly Early Pleistocene) in the surroundings of Fidenza (Emilia-Romagna). Leaves belonging to Acer section Palmata ( Van Gelderen et al. 1994, Grimm et al. 2006, Renner et al. 2008; including close to 50 modern species) from Miocene and Pliocene strata of western Eurasia have been referred to as Acer vindobonensis (ETTINGSH.) BERGER, 1955 ( Ettingshausen 1851, Berger 1955) and A. sanctae-crucis STUR, 1867 ( Stur 1867, Knobloch 1998; Tab. 1). Acer vindobonensis was based on a leaf fragment from Late Miocene strata of Austria ( Ettingshausen 1851; as Sterculia vindobonensis ETTINGSH. ) and described as palmate leaf with five entire margined lobes. Acer sanctae-crucis , described from Middle Miocene strata of Slovakia, has 7-lobed leaves, the lobes being elongate triangular with finely serrate margin. Subsequent authors either treated A. sanctae-crucis as synonym of A. vindobonensis (e.g., Menzel 1906, Zastawniak 1972, KovarEder 1988, Kovar-Eder et al. 1996, Walther and Zastawniak 2005) or as distinct species (e.g., Berger 1955, Iljinskaya 1968, Knobloch 1998). In addition, two fossil-species of sect. Palmata originally described from East Asia were reported from Europe. Of these, A. protojaponicum TANAI et ONOE, 1959 , is distinct by its shallowly lobed leaves, whereas A. nordenskioeldi NATH., 1883 , reported by Berger (1955, 1957), resembles A. vindobonensis ( Tab. 1). Further, Saporta (1873, 1879; see also Andreanszky 1959) used the name of a modern East Asian species for Pliocene (Cantal, France) maple leaves, A. polymorphum SIEBOLD et ZUCC., 1845 (synonym of A. palmatum THUNB., 1784 ), and added pliocenicum without indicating a taxonomic rank. Similarly, Menzel (1906) used the modern name A. polymorphum and added miocenicum.

While it is not the aim of this paper to revise western Eurasian Acer remains of sect. Palmata, we note that most of the taxonomic disagreement between previous authors discussing possible differences or conspecifity between A. vindobonensis and A. sanctae-crucis may be due to the fact that all previous authors compared these fossil-taxa (with the exception of the distinct A. protojaponicum ) to a single modern species, A. palmatum ( A. polymorphum ). One exception is the work by Stur (1867), who indicated similarities with various species of sect. Palmata. Table 1 summarizes leaf characteristics of previously described fossil members of sect. Palmata from western Eurasia and lists similarities to modern species. This is highly informative in the case of A. vindobonense , for which a subentire margin has been refuted (e.g., Walther and Zastawniak 2005), perhaps simply because such a margin is not found in the modern A. palmatum . However, there are other members of sect. Palmata that can be compared with the subentire to remotely serrate leaves of A. vindobonensis , such as Acer sinense ( Tab. 1), which produces leaves nearly identical to A. vindobonensis . Thus, considering a broader set of modern species as possible modern analogues of fossil-taxa, we suggest that a thorough revision of both western Eurasian and East Asian fossil-taxa of sect. Palmata is needed (T. Denk, in preparation).

The specimens from Oriolo differ from previously described fossil-species of Acer section Palmata by the lobe margin, which is serrate along most of the lamina, and by the variable and high number of lobes. According to Tanai (1983), lobe number is taxonomically informative in extant and fossil species of A. sect. Palmata. For example, in A. nordenskioeldi from East Asia, a great number of examined specimens consistently had 5–7 lobes. Among modern members of sect. Palmata, A. sieboldianum produces leaves that match A. aemilianum by its number of lobes and the serrate margin.

During the Middle Miocene to Pliocene, representatives of sect. Palmata were rare elements of several floras in western Eurasia ( Menzel 1906, Knobloch 1969, Kovar-Eder 1988).

Acer sanctae-crucis s. str. might have had its last occurrence in the Pliocene flora of Willershausen, and Acer protojaponicum in the Early Pleistocene of France (ca. 2 Ma; Bernasso; Leroy and Roiron 1996, Girard et al. 2019; Tab. 1). The new record from Oriolo extends the fossil record of sect. Palmata in Europe into the Pleistocene, ca. 0.84 Ma, before it was extirpated from Europe and Asia Minor.

A time-calibrated molecular phylogeny of maples suggested that the Asian members of the Palmata clade ( Grimm et al. 2006) diverged from the single North American member during the Middle Miocene ( Renner et al. 2008). The fossil record further provides evidence that the section was fairly diverse in western Eurasia before it was extirpated in the Pleistocene.

Figures

Text-fig. 13. a, d–g: Acer aemilianum. b, c: Acer palmatum and A. sieboldianum modern leaves (NMNS Cleared Leaf Database). a: Oriolo MSF 661, 7-lobed leaf. b: Specimen U 1049, lobe detail showing finely serrate leaf margin. c: Specimen T 0246, 9-lobed leaf with coarsely serrate leaf margin. d: Oriolo MSF 645-1, 9-lobed leaf with two small additional lobes. e: Oriolo MSF 645. f: Oriolo MSF 660, 9-lobed specimen. g: Oriolo MSF 660-1. White arrows indicate position along lamina lobes where marginal serration starts. Scale bars 10 mm (a–c, f, g), 50 mm (d, e).