This study introduces two new families, one new genus, 22 new species, 10 new combinations, four epitypes, and 16 interesting new host and / or geographical records. Cylindriaceae (based on Cylindrium elongatum) is introduced as new family, with three new combinations. Xyladictyochaetaceae (based on Xyladictyochaeta lusitanica) is introduced to accommodate Xyladictyochaeta. Pseudoanungitea gen. nov. (based on P. syzygii) is described on stems of Vaccinium myrtillus (Germany). New species include: Exophiala eucalypticola on Eucalyptus obliqua leaf litter, Phyllosticta hakeicola on leaves of Hakea sp., Setophaeosphaeria citricola on leaves of Citrus australasica, and Sirastachys cyperacearum on leaves of Cyperaceae (Australia); Polyscytalum chilense on leaves of Eucalyptus urophylla (Chile); Pseudoanungitea vaccinii on Vaccinium myrtillus (Germany); Teichospora quercus on branch tissue of Quercus sp. (France); Fusiconidium lycopodiellae on stems of Lycopodiella inundata, Monochaetia junipericola on twig of Juniperus communis, Myrmecridium sorbicola on branch tissues of Sorbus aucuparia, Parathyridaria philadelphi on twigs of Philadelphus coronarius, and Wettsteinina philadelphi on twigs of Philadelphus coronarius (Germany); Zygosporium pseudogibbum on leaves of Eucalyptus pellita (Malaysia); Pseudoanungitea variabilis on dead wood (Spain); Alfaria acaciae on leaves of Acacia propinqua, Dictyochaeta mimusopis on leaves of Mimusops caffra, and Pseudocercospora breonadiae on leaves of Breonadia microcephala (South Africa); Colletotrichum kniphofiae on leaves of Kniphofia uvaria, Subplenodomus iridicola on Iris sp., and Trochila viburnicola on twig cankers on Viburnum sp. (UK); Polyscytalum neofecundissimum on Quercus robur leaf litter, and Roussoella euonymi on fallen branches of Euonymus europaeus (Ukraine). New combinations include: Cylindrium algarvense on leaves of Eucalyptus sp. (Portugal), Cylindrium purgamentum on leaf litter (USA), Cylindrium syzygii on leaves of Syzygium sp. (Australia), Microdochium musae on leaves of Musa sp. (Malaysia), Polyscytalum eucalyptigenum on Eucalyptus grandis × pellita (Malaysia), P. eucalyptorum on leaves of Eucalyptus (Australia), P. grevilleae on leaves of Grevillea (Australia), P. nullicananum on leaves of Eucalyptus (Australia), Pseudoanungitea syzygii on Syzygium cordatum leaf litter (South Africa), and Setophaeosphaeria sidae on leaves of Sida sp. (Brazil). New records include: Sphaerellopsis paraphysata on leaves of Phragmites sp., Vermiculariopsiella dichapetali on leaves of Melaleuca sp. and Eucalyptus regnans, and Xyladictyochaeta lusitanica on leaf litter of Eucalyptus sp. (Australia); Camarosporidiella mackenziei on twigs of Caragana sp. (Finland); Cyclothyriella rubronotata on twigs of Ailanthus altissima, Rhinocladiella quercus on Sorbus aucuparia branches (Germany); Cytospora viticola on stems of Vitis vinifera (Hungary); Echinocatena arthrinioides on leaves of Acacia crassicarpa (Malaysia); Varicosporellopsis aquatilis from garden soil (Netherlands); Pestalotiopsis hollandica on needles of Cupressus sempervirens (Spain), Pseudocamarosporium africanum on twigs of Erica sp. (South Africa), Pseudocamarosporium brabeji on branch of Platanus sp. (Switzerland); Neocucurbitaria cava on leaves of Quercus ilex (UK); Chaetosphaeria myriocarpa on decaying wood of Carpinus betulus, Haplograhium delicatum on decaying Carpinus betulus wood (Ukraine). Epitypes are designated for: Elsinoë mimosae on leaves of Mimosa diplotricha (Brazil), Neohendersonia kickxii on Fagus sylvatica twig bark (Italy), Caliciopsis maxima on fronds of Niphidium crassifolium (Brazil), Dictyochaeta septata on leaves of Eucalyptus grandis × urophylla (Chile), and Microdochium musae on leaves of Musa sp. (Malaysia).
New Guinea is the world's largest tropical island and has fascinated naturalists for centuries1,2. Home to some of the best-preserved ecosystems on the planet3 and to intact ecological gradients-from mangroves to tropical alpine grasslands-that are unmatched in the Asia-Pacific region4,5, it is a globally recognized centre of biological and cultural diversity6,7. So far, however, there has been no attempt to critically catalogue the entire vascular plant diversity of New Guinea. Here we present the first, to our knowledge, expert-verified checklist of the vascular plants of mainland New Guinea and surrounding islands. Our publicly available checklist includes 13,634 species (68% endemic), 1,742 genera and 264 families-suggesting that New Guinea is the most floristically diverse island in the world. Expert knowledge is essential for building checklists in the digital era: reliance on online taxonomic resources alone would have inflated species counts by 22%. Species discovery shows no sign of levelling off, and we discuss steps to accelerate botanical research in the 'Last Unknown'8.