Introduction

Fellhaneropsis is a small genus currently comprising six species. Most species are obligately or facultatively foliicolous. Two species are restricted to Australia, one is only known from East Asia and two are known from Europe, one of which extends to North America. The two European species are treated by Aptroot & Edwards (Reference Aptroot, Edwards, Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009). They have been rapidly expanding north during recent decades, just as the related Fellhanera species. A good illustration is the situation in Great Britain: in the first edition of the British Lichen Flora (Purvis et al. Reference Purvis, Coppins, Hawksworth, James and Moore1992) only two species of Fellhanera and one of Fellhaneropsis were treated, whereas in the second edition (Smith et al. Reference Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009) six species of Fellhanera and two species of Fellhaneropsis are treated. The situation is similar in the Netherlands; the current four species of Fellhanera and two of Fellhaneropsis have mostly arrived recently and are spreading, not only into new areas but also onto new substrata. Fellhanera viridisorediata Aptroot, et al., which was only described as recently as 1998, is now locally the most abundant lichen species, for example, on reed mats, fences, or on sheltered bark. In all lichen monitoring in the Netherlands, whether on trees or on rock, it has increased. It was absent before the 1980s and has appeared everywhere since (van Herk et al. Reference van Herk, Aptroot and van Dobben2002; Sparrius & Aptroot Reference Sparrius and Aptroot2003). Moreover, it has recently become common on living Rhododendron leaves.

Obligately foliicolous lichens are largely a tropical phenomenon. There are over 800 species known worldwide (Lücking Reference Lücking2008), but less than a dozen are known from Europe; these are mostly species of Strigula (Roux & Sérusiaux Reference Roux and Sérusiaux2004) occurring on Buxus leaves in the Mediterranean. In the past decades there has been a dramatic increase in the occurrence of foliicolous lichens in temperate western Europe (e.g. van den Boom & Sérusiaux Reference van den Boom and Sérusiaux1996; Aptroot & Edwards Reference Aptroot, Edwards, Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009; Lücking et al. Reference Lücking, Wirth and Ahrens2009), especially species of Bacidia and Fellhanera including Fellhanera bouteillei (Desm.) Vězda, one of the two species that was already known to occur on living leaves in western and central Europe in the first half of the last century. The enormous increase of the occurrence of foliicolous lichens in temperate Europe is doubtlessly due to global warming, which has made the climate in these parts warmer and wetter, that is more often humid and for more prolonged periods. This fact has already been recognized for a decade (van Oldenborgh & Komen Reference van Oldenborgh and Komen2001; Heijboer & Nellestijn Reference Heijboer and Nellestijn2002), currently continues (Zorita et al. Reference Zorita, Stocker and von Storch2008) and was also seen a decade ago in changes in epiphytic lichens (van Herk et al. Reference van Herk, Aptroot and van Dobben2002). It is this humid microclimate that allows the growth of species on substrata with a very low water capacity such as living smooth leaves, which could not be colonized under the climatic conditions of only two decades ago. By now, foliicolous lichens are no longer even rare in countries like Germany (Lücking et al. Reference Lücking, Wirth and Ahrens2009) or The Netherlands. They are present in most forests and nature reserves, and even in many gardens. The hosts are mostly non-native trees and shrubs; there are very few indigenous trees and shrubs with suitably evergreen leaves (chiefly Ilex aquifolium, Juniperus communis and Vaccinium vitis-idaea). It is doubtless due to the recent global warming that an obligately foliicolous lichen can be described that is currently only known from a temperate area in Europe. The potential use of foliicolous lichens in central and western Europe as indicators of global climatic change is also stressed by Lücking et al. (Reference Lücking, Wirth and Ahrens2009). Admittedly other factors, such as eutrophication and acid rain, have caused changes in the lichen flora over the past decades, but statistical methods have shown that the effects of these other factors started much earlier than the appearance of foliicolous lichens in NW Europe (van Herk et al. Reference van Herk, Aptroot and van Dobben2002). Acid deposition (especially sulphur dioxide) is thought not to be responsible for recent changes, though its historical pattern is still responsible for regional differences, so that areas which were once subject to heavy pollution still show a poorer lichen flora.

In the nature reserve Witte Veen in The Netherlands, only 300 m from the border with Germany, five foliicolous lichens were found on the living leaves of planted Rhododendron ponticum: Bacidia chloroticula (Nyl.) A.L. Sm., B. delicata (Larbal. ex Leight.) Coppins, B. sulphurella Samp., Fellhanera viridisorediata, and a Fellhaneropsis species. The latter was dominant on the leaves it was growing on, suggesting that it grows rapidly, while the other species present often co-occurred on the same leaves. The Fellhaneropsis differs from all other known species in the genus by the vertically elongated to tubular pycnidia that are fringed with straight, multiseptate hairs. It is described as new to science below.