Fossil Gordonia (s.l.)–like (Theaceae) winged seeds from the early Miocene of the Mecsek Mts, W Hungary

Winged seeds were recovered from two sites of the late early Miocene (Karpatian) flora of Magyaregregy, Mecsek Mts, W Hungary. The seeds are assigned to the fossil-genus and species, Mecsekispermum gordonioides Hably and Erdei gen. nov. et sp. nov., and are tentatively related to the family Theaceae. Based on the overall character of the winged seeds and the isodiametric surface pattern of the seed coat, the seeds are most comparable with species of Gordonia J. Ellis (s.l.,) in Theeae (Laplacea Kunth or Polyspora Sweet). A comparison with winged seeds of other fossil genera, e.g. Saportaspermum Meyer and Manchester, and winged seeds of modern genera in various families is also given. The fossil flora is preserved in the fish scale-bearing clay marl belonging to the Feked Formation and Komló Claymarl Member and dated as Karpatian (late Burdigalian, standard chronostratigraphy).


Introduction
Winged fruits or seeds have frequently been reported in the European fossil record. Disseminules having an apical or lateral wing have been described variously as Cedrelospermum Saporta, Gordonia J. Ellis, Saportaspermum Meyer and Manchester, or Embothrites Unger and have been assigned to various plant groups, e.g. Ulmaceae, Theaceae, and Malvales (Unger 1850;Manchester 1987;Meyer and Manchester 1997;Kvaček and Walther 1998;Kvaček and Wilde 2010). Fruits or seeds assigned to Theaceae are rare not only in the European fossil record but also worldwide. Dilcher (1989, 1992) gave a summary of fossil specimens reported as remains of Theaceae. The earliest fossil fruits assigned to Gordonia (Gordonia lamkinensis Grote and Dilcher and Gordonia warmanensis Grote and Dilcher) were described from the middle Eocene Claiborne flora in Kentucky and Tennessee (Grote and Dilcher 1992;Martínez-Millán 2010).
The classification of the family Theaceae varied in many authors, according to the characters emphasised (Prince and Parks 2001). In the Cronquist system, the family involves~40 genera and 600 species in four subfamilies (Cronquist 1981). Molecular data showed the family as non-monophyletic (e.g. Morton et al. 1996;Soltis et al. 2000), and APG (1998) suggested a narrow definition of the family with Theaceae s.str. and a separate Ternstroemiaceae (Ternstroemieae in Pentaphylacaceae). Based on molecular data, three main lineages of Theaceae s.str. were identified, i.e. Theeae, Stewartieae, and Gordonieae (Prince and Parks 2001). According to the same study, the monophyly of the genus Gordonia was not supported, and sequence data placed its species in Gordonieae (Gordonia s. str.) and Theeae (Laplacea Kunth and Polyspora Sweet). Although a common character of the seeds of Gordonia s.l. species is a prominent flattened apical wing, micromorphological study of the seed coat was used to corroborate the above placement of Gordonia s.l. species (Gunathilake et al. 2015).
Leaves of Theaceae have been reported from some localities in the Northern Hemisphere fossil record during the Cenozoic. Today the area of the family occupies subtropicaltropical Asia and America (Prince and Parks 2001); however, palaeofloristic data indicate the presence of the family also in Europe. Leaf records of Theaceae (s.l.) have been documented in the European floras from the middle Eocene up to the late Miocene. From the middle Eocene flora of Messel (Germany; Wilde 1989) and from the early Oligocene flora of Flörsheim (Mainz Basin, Germany;Kvaček 2004), leaves of two genera, Gordonia and Ternstroemites Berry, were mentioned. Leaves preserved with cuticle were reported as Gordonia hradekensis (Kvaček and Bůžek) Bozukov and Palamarev, Gordonia pseudoknauensis Kvaček, and Ternstroemites floersheimensis Kvaček and Walther from the rich, thermophilous flora. From the early Miocene flora of Hrádek (North Bohemia, Czech Republic;Holy et al. 2012) and from the flora of the Cypris Shale (Western Bohemia, Czech Republic; Bůžek et al. 1996), leaf remains of Gordonia hradekensis were mentioned. From the early Miocene (Ottnangian) flora of Köflach (Austria) ?Gordonia oberdorfensis Kovar-Eder and ?Cleyera schilcheriana Kovar-Eder (Kovar-Eder and Meller 2001) were described based on leaf remains and preserved cuticle. From the late early/early middle Miocene flora of Parschlug (Austria; Kovar-Eder et al. 2004), there are also some leaves assigned to Theaceae, cf. ?Gordonia oberdorfensis and Ternstroemites pereger (Unger) Kovar-Eder and Kvaček. From the middle Miocene (Badenian) of the Satovcha Graben in the Western Rhodopes (Bulgaria), Bozukov and Palamarev (1995) described a flora as a rich refuge of the representatives of Theaceae (s.l.), e.g. Eurya aff. acuminatissima Merril and Chun, Gordonia hradekensis, Gordonia stefanovii Palamarev and Bozukov, Hartia palaeorhodopensis Bozukov and Palamarev, Stewartia stefanovii Palamarev and Bozukov, and Stewartia submonadelpha Tanai and Onoe. In Europe, Theaceae presumably survived up to the late Miocene or Pliocene based on reports from the Sessenheim flora in France (Geissert et al. 1990), Fritzlar (Hessen) in Germany (Hottenrott et al. 1996), and refuge areas of the Pannonian Basin. A rich late Miocene thermophilous flora was described from Mataschen (Austria, Kovar-Eder and Hably 2006) with four species assigned to Theaceae. Gordonia emanuelii Kovar-Eder, Gordonia pannonica Kovar-Eder, Gordonia styriaca Kovar-Eder, and Schima mataschensis Kovar-Eder were described based on leaf remains with cuticle. The flora of Magyaregregy also yielded leaf remains described as Ternstroemites pereger, which may be related to the Theaceae (s.l.) family (Hably 2020).

Geology
The area of the Mecsek Mts is situated in the SW Pannonian Basin, on the Tisza-Dacia Megaunit, a tectonic block south of the mid-Hungarian Shear Zone. The Neogene stratigraphy of the Mecsek area was summarised by Hámor (1970), Chikán (1991), and Barabás (2010Barabás ( , 2011. Widespread lower Miocene fluvial clastics (Szászvár Formation) are overlain by the Budafa Formation, traditionally regarded as of Karpatian (late Burdigalian) age (Gyalog 1996;Gyalog and Budai 2004;Budai et al. 2015). The Budafa Formation consisted of three members, the Komló Claymarl Member, Pécsvárad Limestone Member, and the overlying Budafa Sandstone Members. The succession is overlain by Badenian (Langhian) Leitha limestones in the littoral zone and offshore sands and silts in the basins, locally with coalbearing swamp deposits along the shores. Based on the absence of marine fossils in the Pécsvárad Limestone and in most part of the Komló Claymarl, Sebe et al. (2019) concluded that these rocks are lacustrine deposits. As suggested by the lake sediments and its fauna, instead of a system of smaller lakes, a contiguous water body, called "Lake Mecsek", existed in the area from the Karpatian up to the early Badenian according to K/Ar age and biostratigraphic dating of the overlying marine deposits (Sebe et al. 2019). The Pécsvárad and Komló Members are both interpreted as lake deposits and differ very much from the Budafa Sandstone Member; therefore, Sebe et al. (2019) united the two members as a separate formation, the Feked Formation.
Consequently, the "fish scale-bearing clay marl" sediments preserving the plant fossils belong to the Feked Formation and Komló Claymarl Member, dated as Karpatian (late Burdigalian) (Sebe et al. 2019). It is composed of dark grey, greenish-grey, massive, or laminated silty clay marl, calcareous silt, and fine sands, with numerous fish scales and bones, and sometimes with tuff interbeds. K/Ar dating measurements from tuff interbeds within the Komló Claymarl showed an age of 16.82 ± 0.65 Ma, i.e. Karpatian (late Burdigalian) (Sebe et al. 2019).

Material and methods
The fossil seeds (14 specimens) are preserved mostly as impressions in the fish scale-bearing clay marl. Owing to the fine-grained sediment, morphological details of some seeds are well-preserved. Fossils are stored in the palaeobotanical collection of the Hungarian Natural History Museum, inventoried with an epithet "HNHM-PBO". For microscopic studies, an Olympus SZX9 dissecting microscope equipped with an Olympus DP72 digital camera was used. For comparisons, modern seed material of the herbarium of the HNHM and digitized herbarium material through JSTOR Global Plants Diagnosis: Winged seed, consisting of asymmetric, elongate ovate seed body and apical, flattened, elongate wing. Length of winged seeds 0.9-1.7 cm, width up to 0.6 cm, wing distally rounded. Wing swelling on ventral side (ventral side concave). Wing without scars, veins or any ornamentation, wing margin smooth. Length of seed body up to 0.7 cm, width up to 0.25 cm, oriented with long axis at about 20°angle to long axis of wing. Basal part of seed body rounded, apical part acute. Surface cell pattern of seed coat on wing isodiametric, without ridges or protrusions.

Discussion
The remains are most probably seeds suggested by the lack of veins on the wing (see argumentation by Meyer and Manchester 1997). Some of the seeds (e.g. the holotype, HNHM-PBO 2017.98.1; Fig. 1a-b) show a somewhat angular seed body which may refer to its development in a fruit. The dorsal margin of the wing seems to be more thickened than the ventral margin.
Winged fruits or seeds showing comparable gross morphology to Mecsekispermum seeds (i.e. equipped with an apical or lateral wing) have been variously described in the fossil record as Cedrelospermum, Gordonia, Saportaspermum, or Embothrites (Unger 1850;Manchester 1987;Meyer and Manchester 1997;Kvaček and Walther 1998;Kvaček and Wilde 2010). Seeds were described as cf. Gordonia sp. in Kundratice (Czech Republic), but Kvaček and Walther (1998) noted that similar seeds have been described as Saportaspermum occidentale Meyer and Manchester from the Oligocene Bridge Creek flora of OR, USA (Meyer and Manchester 1997). Later, Kvaček and Walther (2004) described winged seeds resembling the material from Kundratice as Saportaspermum sp. from the nearby locality of Bechlejovice (Czech Republic) and noted that "Similar seeds are produced by various Sterculiaceae (e.g. Reevesia Lindl.)". The seeds described from Kundratice as cf. Gordonia sp. and from Bechlejovice as Saportaspermum sp. show similar morphology and most probably represent the same species of Saportaspermum. This is supported also by the fact that sediments of the two localities represent the same formation (Ústí Formation) of the České Středohoří (Cajz 2000); they are coeval, early Oligocene and floristically quite similar in sharing many taxa (Teodoridis and Kvaček 2015). Studies published later assign Saportaspermum to the Malvaceae family (Kvaček 2006), but its taxonomical position is uncertain. This extinct genus was typified with Saportaspermum occidentale (Meyer and Manchester 1997) from North America.
In the flora of Parschlug (Austria), there are several specimens of Saportaspermum varying in morphology (Kovar-Eder et al. 2004). All the seeds mentioned above show characters similar to Saportaspermum, described by Meyer and Manchester (1997). We refrain to accommodate winged seeds from Magyaregregy in this genus since their morphological traits differ from characters mentioned in the protologue of Saportaspermum (Meyer and Manchester 1997). In Saportaspermum seeds, the seed body is more rounded contrasting the elongate ovate seed body of Mecsekispermum. In Saportaspermum, the ventral and dorsal margin of the wing are more or less parallel contrasting Mecsekispermum seeds, in which the wing is swelling (rounded) on the ventral side of the seed giving a concave appearance to the ventral wing margin. In Mecsekispermum seeds, the wing is oriented with its long axis at a very shallow angle (up to 20°) to the long axis of the seed body contrasting seeds of Saportaspemum displaying larger angles (30-40°). Although seeds assigned to Saportaspermum may represent various plant groups, many of them seem to represent malvalean plants (Kvaček and Wilde 2010).
Samaras of Cedrelospermum (Ulmaceae, also occurring in Magyaregregy, see in Hably 2020) are different in showing a characteristic V-shaped stigmatic notch distally, in having, though not always, a secondary wing and subparallel veins converging towards the distal end of the wing (Manchester 1987).
Specimens described as Embothrites borealis Unger from the Eocene flora of Socka (Unger 1850) has rounded seed body, and the wing showing fine dichotomous venation is attached to the seed with a neck contrasting Mecsekispermum seeds. Some of the E. borealis specimens (Unger 1861) were transferred to the ulmaceous genus Cedrelospermum (Manchester 1987).
Fossil seeds along with the leaves of Cedrela P. Browne (C. merrillii (Chaney) Brown) were described by Meyer and Manchester (1997) from the Oligocene Bridge Creek flora in Oregon (North America). These seeds show similarities to the seeds of Mecsekispermum in the attachment of the seed body and wing; however, they are quite variable in the form of seed body and wing contrasting seeds from the Mecsek. The fossil Cedrela seeds show the characteristic form of modern Cedrela seeds, with crescent-form wing and elongate seed body ( Fig. 2k-l).
Compared with modern genera, the fossil seeds from Magyaregregy display a gross morphology most comparable with the seeds with apical flattened wing of Gordonia s.l. species of Theeae in the Theaceae family (Polyspora and Laplacea species) (Fig. 2a-c), e.g. G. haematoxylon Sw., G. lanceifolia Burkill, G. luzonica S.Vidal, G. papuana Kobuski, G. tonkinensis Pit., and G. wrightii (Griseb.) H.Keng). The attachment of seed body and wing including their relative orientation, the shape of seed body and wing, and their ratio agrees with those of modern Gordonia seeds. The isodiametric pattern of the seed coat above the wing (Fig.  1d) is in agreement with that observed in Gordonia s.l. species of Theeae by Gunathilake et al. (2015). The seed coat of species in Gordonieae (G. lasianthus (L.) J.Ellis and G. brandegeei H.Keng) shows protrusions though it is not consequently present on the wing (Gunathilake et al. 2015). Our seeds show an intermediate size between the size ranges of Gordonia s.l. seeds in Gordonieae and Theeae.
There are several modern genera in various families which produce winged seeds or fruits equipped with an Rakotoar. and Andriamb. and Callm.; Fig. 2g) show somewhat similar morphology to Mecsekispermum seeds, but dorsal and ventral margins of the wing run parallel and straight. The long axes of the seed body and the wing are oriented at higher, 60-80°a ngle to each other. In the seeds of Pterygota Schott and Endl., the wing is ornamented. Winged seeds of Pterospermum species (e.g. P. aceroides Wall., P. argenteum Tardieu, P. grewiifolium Pierre, P. lanceifolium Roxb. ex DC., P. heterophyllum Hance, P. macrocarpum Hochr., P. pecteniforme Kosterm., P. proteus Burkill, P. reticulatum Wight and Arn., P. semisagittatum Roxb. ex DC., P. truncatolobatum Gagnep.; Fig. 2h) have a rounded seed body and a wing much longer compared with the seed body. In seeds of Reevesia species (e.g. R. clarkii (Monach. and Moldenke) S.L. Solheim ex Dorr, R. glaucophylla Hsue, R. macrocarpa H.L.Li, R. pubescens Mast., R. tomentosa H.L.Li; Fig. 2f) wing shape is different from that of the fossil seeds; ventral side of wing is straight, whereas dorsal side shows prominent swelling.
In the family Salicaceae, winged seeds of the genus Carrierea (e.g. C. calycina Franch.; Fig. 2j) have a broader wing compared with seed body and wing length.
Since the morphology of the winged seeds from Magyaregregy does not agree with any fossil winged seeds described hitherto, we establish a new genus, Mecsekispermum. Winged seeds (with apical wing) from Paleogene and Neogene floras have usually been included in the genus Saportaspermum. We think that seeds from Magyaregregy, which are morphologically distinct from Saportaspermum seeds described so far, should not be assigned to this genus. In addition most of the Saportaspermum seeds seem to have malvalean affinities, and describing seeds of presumably non-malvalean affinities in this genus would not be practical. The similarity of Mecsekispermum seeds to seeds of some modern Gordonia species is emphasised, but with the lack of clear evidence, we do not assign them to the modern genus Gordonia. There are other, co-occurring leaf and fruit (capsule) remains at the locality, described as Ternstroemites pereger and Carpolithes gergoei Hably and Erdei (Hably 2020), which may be related to the Theaceae family; however these, due to uncomplete or poor preservation, do not contribute with additional information to the systematic assignment of the seeds.

Conclusions
Winged seeds are described from the early Miocene flora of Magyaregregy, Mecsek Mts, Hungary. Since the seeds are different from other fossil-winged seeds and unequivocal evidence for the systematic relation of the fossils to modern genera does not exist, a new fossil genus and species Mecsekispermum gordonioides is established. Based on some shared characters including seed body and wing morphology and the surface pattern of the seed coat, the seeds are tentatively compared with Gordonia s.l. species in Theeae (Theaceae).