Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 37

The Palaeocene flora of Mull, Scotland, originally described by Gardner (1887) is the only Paleogene BIP flora that has been revised in more recent years (Boulter and Manum 1989; Figures 1 and 2). The age of the intrabasaltic plant‐bearing sediments of Mull has been radiometrically dated at 60–58 Ma (Chambers and Pringle 2001).

Among riparian and wetland elements, the ferns Dennstaedtia, Onoclea and Osmunda were widespread in Paleogene Arctic plant assemblages, commonly co‐occurring with Metasequoia. Among the diverse gymnosperms, Ginkgo gardneri Florin represents a lineage more closely related to Mesozoic ginkgoes than to the Cenozoic Ginkgo adiantoides (Ung.) Heer from Europe and Svalbard (Denk and Velitzelos 2002). Further, Amentotaxus, cf. Cephalotaxus, Glyptostrobus, Elatocladus (with affinities to modern Taxodium and Sequoia), Metasequoia and Pinus and cf. Tsuga are recorded (Boulter and Kvaček 1989; Kvaček 2010). Platanites hebridicus Forbes is an extinct Platanaceae distinct from the coeval Platanus schimperi (Heer) Saporta and Marion of Gelinden (Belgium; Mai 1995) and Platanus aff. leucophylla (Unger) Knobloch from western Greenland. The genus Platanites has also been recorded from the Paleogene of Saskatchewan (Canada; McIver and Basinger 1993) and possibly from the Eocene of north‐western Wyoming (Crane et al. 1988). In addition, few pentafoliate leaves and leaflets belong to the extinct Platanus subgenus Glandulosa Kvaček, Manchester and Guo. These were assigned to Platanus fraxinifolia (Johnson and Gilmore) Walther by Boulter and Kvaček (1989) in contrast to the trifoliate leaves of P. bella from Greenland.

Common elements of Mull, mostly shared with the floras of Greenland, are Trochodendroides (and rare Ziziphoides), betulaceous leaves of Corylites [shared with Svalbard], Fagopsiphyllum groenlandicum (Heer) Manchester [as Fagopsis groenlandica (Heer) Wolfe; shared with the floras of Greenland and Svalbard], Ushia olafsenii (Heer) Boulter and Kvaček, Juglandiphyllites spp., foliage with affinity to Fagaceae (Castanopsis, Lithocarpus, Quercus sect. Cyclobalanopsis [as Camptodromites spp.] and Macclintockia. A number of taxa not found in other BIP floras are the distinct foliage of Davidoidea (similar to Platanaceae, Hamamelidaceae and Euptelea) and of Vitiphyllum with affinities to Vitis along with a flower of unclear taxonomic relationships (Calycites).

Similar floras are known from Isle of Skye, Scotland (Poulter et al. 2008, 2010) and Ballypalady (County Antrim, Ireland; Mai 1995). In the latter flora, cones of Pinus plutonis Baily are abundant and biogeographically interesting. According to Mai (1995), P. plutonis belongs to section Sylvestres subsection Resinosae and provides another potential link between Europe and North America.