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recent years. Kloppenburg (1991) suggested that the Philippines might have in excess of 
30 species, a number that has since climbed to 104 species (Aurigue et al., 2013) with a 
further 80 new taxa published since 2013 (IPNI, 2016). However, the actual number of 
species in the Philippines is pending a critical revision. Forster et al. (1998) noted the 
species diversity of Hoy a in Borneo was ‘unknown’ but recent research has since led to 
the description of numerous new species in preparation for a comprehensive revision 
(Rodda & Nyhuus, 2009; Rodda et al., 2011, 2014a, 2014b, 2015, 2016; Rodda & 
Simonsson, 2011a, 2011b; Rodda & Simonsson Juhonewe 2013a, 2013b; Lamb et al., 
2014; Rahayu et al., 2015; Rodda, 2015; Lamb & Rodda, 2016), and a checklist that 
includes 71 species and one subspecies (Lamb & Rodda, 2016). 
The island of New Guinea has 74 species according to Forster (1996), mostly 
described in the first half of last century. Papuasia lies towards the eastern edge 
of the distribution area of the genus Hoya and includes the Papua and West Papua 
provinces of Indonesia, Papua New Guinea (PNG), and the Solomon Islands. The 
largest land mass is the island of New Guinea, the largest tropical island in the world. 
Major contributions to Hoya of New Guinea were published by Schlechter, almost 
entirely based on his own collections obtained during expeditions between 1901 and 
1909 (Schlechter, 1905, 1908, 1913). Schlechter’s collections are limited to German 
New Guinea, now part of PNG. Moore (1916) described numerous Hoya species 
from Indonesian New Guinea, based on specimens collected by Boden Kloss. For the 
Solomon Islands Hoya species were first published by Hemsley (1891, 1892, 1894). 
The most recent contributions to the Hoya of New Guinea were published by 
Forster & Liddle (1991, 1992, 1993) and Forster et al. (1995). Forster et al. (1997) 
described the monotypic genus Madangia PI.Forst., Liddle & I.M.Liddle which has 
since been synonymised into Hoya (Wanntorp & Forster, 2007). 
Despite the large number of species already recorded, the Hoya diversity of 
PNG is still poorly known. Early exploration was focused mostly in Madang and 
Morobe Provinces of PNG (Forster, 1996), leaving much of the island unexplored and, 
consequently, the likelihood of large numbers of new taxa yet to be discovered (Forster 
1996; Prance et al., 2000). Indonesian New Guinea is overall much less explored 
than PNG (Forster, 2006) and only 16 species have so far been recorded from both 
Indonesian New Guinea and PNG (Forster, 1996, 2006). 
The island of New Guinea is dominated by the mountain ranges that run the 
length of the island. These mountains can exceed 3000 m and divide the island in a 
cratonic southern half and accreted terranes to the north (Brown et al., 2006; Heads, 
2006). The varied topography, in combination with ever-wet versus monsoonal 
climate zones (Whitmore, 1984; Van Welzen, 1998), offers a large number and variety 
of biogeographic zones that support high species richness, as observed for example in 
orchids (Vollering et al., 2016) and Rhododendron (Brown et al., 2006). Despite the 
lack of biogeographic data on Hoya , based on our observations the lowland rainforests 
and lower montane forests appear to harbour the majority of Hoya species, while the 
montane forests have a high percentage of local endemics. Only a very few species 
go beyond 2000 m, most notably Hoya krusenstierniana Simonsson & Rodda (here 
