Cycadaceae - Central Province

The unknown hoyas and its sister genera

  of Papua New Guinea

Hoya patella is a very popular species native to the cloud misted mountains of New Guinea.

World's biggest hoyas  and eriostemmas come from the island of New Guinea. The photo shows Hoya cf. gigas NS05-195 (sect. Eriostemma) with 11 cm big flowers, which I encountered in 2005.

Hoya stenophylla had apparently not been re-collected for nearly 100 years. I saw this one (NS08-030) on a fallen tree in Morobe Province, which may be H. stenophylla which has linear, thin leaves on climbing vines with big flowers.


Island of New Guinea is one of Earth's most biologically rich places. A 5000 metres tall mountain range runs along the entire island, creating a rugged terrain with a great number of isolated micro-climatic zones. There are many species with specific habitat requirements created over the time in those isolated zones. Those species are most unique for this island.

'Paradise Forests' is a popular name for the island New Guinea's huge tracts of beautiful ancient forests (= primary forests) also possessing an unique fauna like bird of paradise, cassowaries, tree kangaroos and many unique tree-dwelling marsupials.

New Guinea has a great deal of all known species of Hoya and its sister genera eg. Dischidia. The right part of island, the country of Papua New Guinea, has presently about 70 species of Hoya. Some 90% of these have never been found outside the island. Yet, only a few botanists have covered a small fraction in PNG, of which most occured 100 years ago!

If you see 200 specimens of these sister genera during a trek in the forest, usually only one of the specimens is in flower. Remaining 199 have been neglected by the few botanists without any record. Tribal disputes and cannibalism have scared biologists off for a long time, however the cannibalism is no longer practised.

Therefore the inaccessible landscapes of PNG most likely still possess a good number of unknown species.

PNG is the last frontier and has the most unique species.

The virgin forests in the entire distribution range of these genera (India and Southeast Asia to Samoan islands) have declined dramatically lately, causing a loss of more than 50% of natural habitat for all these three genera.

Only a few species of Hoya appear to be able to re-colonize within a decade or two, suggesting the most species in Hoya to be vulnerable. There is no scientific data yet on this, and the reasons are still relatively unknown.

Therefore there is a great need for a survey dealing with the vulnerability, climate requirements, population sizes, distribution area, and collecting living material for ex situ conservation. This survey would reveal new species, and DNA would be accessible for further studies within these genera, and shed a light on the reasons of their vulnerability.

This is specially important for PNG which is one the least explored countries, and in PNG most hoyas still exist, whereas in Southeast Asia you can only study small fractions of the flora that once existed.

The new findings are expected to be unique for PNG, as there are many species from New Guinea with morphological features not seen elsewhere (e.g. Hoya archboldiana, H. gigas, H. hypolasia, H. inflata, H. lauterbachii, H. megalaster, H. microphylla, H. onychoides). Most of them have exceptionally huge flowers and very ornamental. Actually, all but about three species with flowers exceeding 5 cm (2 inches) are from New Guinea. Why has this island got so huge flowers?

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