Intersectional polyphyly of the puzzling Scapania obcordata (Marchantiidae) suggests convergent evolution: resurrection and European occurrence of S. jensenii

Abstract

We present an example of morphological convergence among two species of Scapania that were considered to be conspecific. We resurrect S. jensenii from synonymy with the morphologically and molecularly variable S. obcordata because our molecular data show that they are distantly related. Chloroplast trnL-trnF and nuclear ITS sequences resolved S. obcordata in sect. Curtae and S. jensenii in sect. Apiculatae sister to S. obscura and we detected morphological differences in secondary pigmentation and leaf anatomy. The similarity comprises the absence of a pronounced keel in vegetative leaves and a weakly defined stem cortex. These features are virtually unknown in other species of Scapania and probably result from convergence in adaptation to the same environmental conditions, as both taxa inhabit alluvial plains characterised by regular disturbance by flooding and covering with sand and silt. While S. obcordata is widespread in the northern Holarctic and known from the Antarctic, S. jensenii is known from a few localities in Greenland, mainland Norway, the Chukchi Peninsula and the Swiss Alps. Its rarity, the absence of female plants, and the lack of genetic variability suggest that S. jensenii underwent a bottleneck event.