Leaf Architecture of Extant Species ofRosaL. and the Paleogene SpeciesRosa lignitumHeer (Rosaceae)

Abstract

Leaf fossils of Rosa lignitum Heer have often been documented as an accessory element in mixed mesophytic forests from the Oligocene and Miocene of central Europe. Its relationship to extant rose species is not yet firmly understood because leaf morphology contributes only marginally to the current taxonomy of the genus Rosa L. In this study, we investigate which extant rose species have structural leaf characters most similar to those of R. lignitum and whether the distribution and ecology of these extant species fit with the conditions hypothesized for the paleovegetation containing R. lignitum. Therefore, we examined the leaf characters of 32 extant rose species for their diagnostic value in taxonomy and compared these data with characters observed in R. lignitum from five Paleogene floras in central Europe. Most remarkably, we detected semicraspedodromous venation in R. lignitum. This venation pattern was found only in a few species of Rosa distributed in Southeast Asia, whereas the majority of extant rose species developed strictly craspedodromous venation. The distribution of extant species with semicraspedodromous venation in mixed broad-leaved deciduous and evergreen forests in subtropical China clearly corresponds to the hypothesized mixed mesophytic forests in the European paleovegetation. Thus, this study of detailed leaf morphology of Rosa again supports the previous assumption that the zonal vegetation of the central European Oligocene is partly comparable to extant forest types in Southeast Asia.

A Miocene leaf fossil record of Rosa ( R. fortuita n. sp.) from its modern diversity center in SW China

“…Wendl., R. helenae, and R. roxburghii Tratt. (Kellner et al, 2012). In this study, 39 out of 49 studied extant Rosa species native to China have semicraspedodromous venation, which further supports Kellner's conclusion (Appendix).…”

“…are similar to those of R. lignitum Heer, a species being widely reported from the Oligocene to Miocene in central Europe (Kellner et al, 2012). Many plant species went extinct or were restricted to small regions in Europe during the dramatic climate changes since the Pliocene (Kovar-Eder, 2003), whereas the complex topography in southwestern China may have protected the survival of many plants, including Rosa, from climate change by allowing plant communities to migrate to regions with suitable environmental conditions.…”

“…Among the 49 extant species of Rosa that were studied, the number of leaflets in one compound leaf ranges from three to 13 (Fig. 3 Kellner et al (2012) proposed that there are two possible venation patterns of secondary veins in Rosa, craspedodromous and semicraspedodromous. The semicraspedodromous venation type usually occurs among species in Asia, e.g., R. banksiae, R. bracteata J.C.…”

“…Until now, only a few Rosa fossil records of whole leaves with good preservation have been reported. R. lignitum Heer, a species from the Oligocene and Miocene of central Europe, has leaflets with rounded apices (Kellner et al, 2012), whereas R. fortuita n. sp. has leaflets with acute apices ( Fig.…”

“…An intact compound leaf could provide evidence to assign the fossil to Rosa, but relatively few whole leaf fossils have been reported. The exceptions are R. lignitum Heer from the Oligocene and Miocene in Central Europe (Kellner et al, 2012), and R. hilliae Lesquereux from the Eocene and Oligocene of USA (Meyer and Manchester, 1997;Meyer, 2003). There has never been a whole leaf Rosa fossil reported from China.…”