Hoya of Papuasia I. 
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published) that inhabits the cold upper montane forests from 1800 m up to 2600 m. 
That is surprisingly high, since Hoya has its upper limit at 2200 m on both Borneo 
and Sumatra (Lamb & Rodda, 2016). Above 2600 m, in the sub-alpine vegetation, no 
Hoya species have so far been discovered. Along the shoreline, with rough conditions 
such as saline winds, strong sun exposure and little shade, there are only a few Hoya 
species capable of growing, although often quite abundantly. These coastal species are 
widespread all along New Guinea’s coastline and its outlying islands, e.g. Hoya anulata 
Schltr., H. australis R.Br. ex J.Traill, H. globulifera Blume, H. nicholsoniae F.Muell., 
H. inconspicua Hemsl. and H. ischnopus (Warb.) Schltr. The coastal species, being 
common and easily accessible, are thus the most abundantly represented New Guinean 
species in herbaria and were also the most frequently encountered species during the 
first author’s expeditions in lowland PNG. As these species are hardy, widespread, 
and tolerant of weather extremes, they have also been sighted on big trees in cities, in 
gardens, in secondary forests and even growing up to 1400 m (except H. inconspicua 
that is limited to the lowlands). In contrast, almost all other Hoya species are confined 
to primary forests or their margins and are often absent from secondary forests. They 
are thus vulnerable due to forest clearance for agriculture and timber harvesting. Except 
for the widespread coastal species, there is almost no overlap between species in the 
highlands and lowlands. There are two common montane species that are capable of 
growing outside of primary forests, recolonising secondary forests and even growing 
on trees in villages and gardens; these are H. solaniflora Schltr. and H. subglabra 
Schltr. Both species are frequently seen in bright locations between 1500 and 1800 m 
all over the Highlands in PNG. 
New Guinea has several species complexes of similar taxa that may turn out to 
be fewer variable species once more collections are gathered from the more remote 
areas of the island. These complexes include the Hoya ischnopus complex (which 
includes H. dimorpha F.M.Bailey, H. dischorensis Schltr., H. flavescens Schltr., H. 
kenejiana Schltr. and H. montana Schltr.) and the H. globulifera complex (including 
H. lamingtoniae F.M.Bailey and H. rubida Schltr.). A third more challenging group 
includes all members of Hoya section Eriostemma Schltr. which are co mm on and 
widespread throughout the Malesian region and Papuasia. Species delimitation within 
this section is particularly problematic. 
New Guinea’s Hoya species harbour several extremes of morphology for 
the genus, including the smallest leaved species such as Hoya microphylla Schltr., 
H. pulchella Schltr., H. oxycoccoides S.Moore and H. krusenstierniana. The largest 
flowers are recorded from New Guinea, Hoya gigas Schltr. and H. lauterbachii 
K.Schum., and the almost as large, newly discovered, H. stenakei Simonsson & Rodda. 
The majority of New Guinea’s species of Hoya have large (occasionally > 3 
cm), campanulate or urceolate corollas. Even species forming small plants such as 
Hoya pulchella , H. patella Schltr. and H. juhoneweana ssp. lindforsiana Simonsson & 
Rodda have large flowers. This is not observed in Borneo or Philippine Hoya , where 
the majority of species have reflexed (Borneo) or revolute (Philippines) corollas and 
only a few taxa have campanulate corollas. 
