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Michael Ferrero has invited me to contribute an informal series of articles on my trip to PNG in July and August 1996. During six weeks at Port Moresby and in Madang, Oro and Milne Bay Provinces I was told about or saw nine types of cycads. These might be different species (I saw Cycas campestris, C. rumphii and C. schumanniana) or intergrades. An intergrade is a plant showing features of two species despite the fact that one of the species does not occur in the area.
Let me backtrack. After my return, I attended a meeting of PACSOA where Ken Hill of Sydney Botanic Gardens gave an excellent illustrated lecture on the genus Cycas in Asia. He later sent me a copy of his fascinating article on the Cycas rumphii complex in PNG. Hill erected a new division of the genus Cycas for C. rumphii and related species (apoa, bougainvilleana, micronesica, schuman-niana and seemannii) and published the type descriptons of apoa, bougainvilleana and micronesica.
A shared feature of the C. rumphii group is a spongy flotation layer in the seed which facilitates an aquatic dispersal mechanism. The seeds float! This layer is also found in Cycas circinalis and Cycas thouarsii. The presence of the layer in all eight species could have been caused by their descent from a common progenitor or convergent evolution (independent development of the same feature in unrelated populations). Natural forces can scatter floating seeds widely. The colonists' flowering produces a population of variable hybrids. There will be no sign of the source of the hybridism when the colonists die. Later storms can cause further injections of foreign genetic material. A distribution map in Ken Hill's article shows that interspecific intergrades occur through a wide area of Melanesia.
I spoke to Roy Osborne at the March PACSOA SQG meeting. His opinion is that the intergrades are possibly the product of prehistoric distribution ranges of species being larger than they are now. A new assay technique will allow the parentage of intergrades to be definitively determined. Given that some cycad seeds are used as food in PNG and that long distance canoe routes existed in prehistory, some seeds may have been transported by human agency.
How does this relate to my trip? I spent 11 days at Tuff in Oro Province with the nice people who run the Konambu Guesthouse.
In the village was a cycad around 750 mm in height. Its leaflets were recurved. As they grew out from the rhachis, they reached a certain point and curved towards the trunk. I never saw the mature plants on the mountain. It was just too far. I walked up there twice and saw many birds, including hornbills, but the only cycads were seedlings. An immature plant beside the track caught my attention because its leaves were undulate like Cycas apoa! The larger plant at Konambu village did not have undulate leaves. The range of C. apoa extends from the Huon Peninsula in Morobe Province to points west in Indonesia. Tuff is a long way east of the Huon Peninsula. Tufi's mostly rocky coastline seemed inhospitable to floating cycad seeds and I thought the Tuff cycad was a new species. I now believe it is an intergrade between C. scratchleyana and C. bougainvilleana with maybe a gene of C. apoa included.
Tony Huntington from Palms & Cycads No. 58, Jan-Mar 1998