Rhododendron ponticum L. var. sebinense (SORDELLI) SORDELLI in the Late Pleistocene flora of Hötting, Northern Calcareous Alps: witness of a climate warmer than today?

The Pleistocene flora of Hötling (Northern Calcareous Alps, Austria) has traditionally been considered an indicator of an interglacial climate warmer than the present one. This was based mainly on the presence of rhododendron leaves and bud scales belonging to the ' Rhododendron ponticum group'. Rhododendron ponticum displays a Euxinian (areas along the southern Black Sea coast) - Iberian (Spain, Portugal) disjunct distribution at present. Based on leaf morphological characteristics the Pleistocene R. ponticum var. sebinense clearly is more similar to the modern eastern subsp. ponticum (Turkish and Caucasian populations) than to the western subsp. baeticum (Iberian Peninsula). In view of the Cainozoic occurrence of fossils similar to modern R. ponticum in Bulgaria and the Northern Caucasus, the eastern ränge of the species is suggested to be older and the present disjunction to be of Pleistocene age. To assess the importance of R. ponticum var. sebinense for palaeoclimatic considerations, approximate mean annual temperatures were inferred for Stands of R. ponticum subsp. ponticum at high elevations with the moist adiabatic lapse rate (suggesting a temperature decrease of about 5°C/10()0 altitudinal metres for humid temperate areas). The inferred mean annual temperatures suggest that the presence of R. ponticum var. sebinense in the Pleistocene of Hötting does not necessarily point to an interglacial climate warmer than today in this area. Further, the Rossfall-Lahner and the Hungerburg floras representing two distinct lithotypes within the 'Höttinger Breccia' were analysed. Using indicator values for Central European plants shows that the majority of taxa encountered in both floras are classified as 'indif-ferent' with regard to mean annual temperature requirements or corresponding to the present Situation, and that the co-occurrence of "subalpine" and lowland taxa may simply reflect the broad contact zone between such taxa found in alpine environments (such as alpine taxa extending to lower elevations on vertical stripes of scree). Based on the floral composition of the Hungerburg and the Rossfall-Lahner assemblages it cannot be ascertained whether the fossilif-erous Sediments were deposited at the same time or not, nor from which interglacial they were deposited. 1000 Höhenmeter um ca. 5°C abnimmt (moist adiabatic lapse rate). Ausgehend von der erhaltenen Jahresmitteltemperatur kann vermutet werden, dass das Vorkommen von R. ponticuw var. sebinen.se nicht notwendigerweise auf höhere Temperaturen für das Inlergla/. ial von Hötting schliessen lässt. Die Floren von Rossfall-Lahner und Hungerburg wurden analysiert, welche innerhalb der Höttinger Breccie unterschiedliche Lithotypen repräsentieren. Temperaturwerte für zentraleuropäische Pflanzen zeigten, dass ein Grossteil der in beiden Floren vorkommenden Taxa bezüglich ihrer An-sprüche an die Jahresmittcltemperatur als indifferent eingestuft werden oder der heutigen Situation entsprechen. Wei-ters zeigte sich, dass das gemeinsame Vorkommen subalpiner und Tieflandstaxa die breite Kontaktzone solcher Arten in alpinen Lebensräumen widerspiegelt (beispielsweise alpine Taxa, die in oder entlang von Geröllhalden bis in Tiefla-gen reichen). Die Artcnzusammensetzung der Hungerburg und Rossfall-Lahner Vergesellschaftungen liefert keine In-dizien dafür, dass diese Sedimente zur gleichen Zeit oder während unterschiedlicher Phasen des Pleistozäns abgelagert wurden. Daher kann eine präzise zeitliche Einstufung der Höttinger Interglazialflora derzeit nicht gemacht werden. of Rhododendron Hötting biogeographical 'R. floristic affinities The fruiting bodies of Xylaria grow from the bases of rotten stumps in forests and differ substantially from the present specimens in their irregulär size and shape. In contrast. compansons to modern material of Rhododendron ponticum confirm WETTSTEIN'S (1892) inter-pretation.