It’s not unusual for populations separated by vast distances to show variation in form, after all this is how we believe many new species originate. However the variation between two populations of Ficus adenosperma, one in Eastern Qld and the other in Litchfield NT, suggest there is something more than mere geographic isolation at play. Berg and Corner (2005) described adenosperma as growing along the north-eastern coast of QLD and islands to the north of Australia, Solomon Islands, New Hebrides, Moluccas and New Guinea. The description noted variation in the amount of hair on the leaves, the Qld population being mostly hairless, while other populations are distinctly hairy. No where in the description is it mentioned that this species has hollow stems, something I would think is an important identifying feature, nor is it mentioned that adenosperma grows in the Northern Territory.
The accepted distribution of Australian adenopserma includes Litchfield National Park and the north-eastern tip of NT, which may be valid records though something has me wondering if they’re correctly identified. Dixon (2011) in Flora of the Darwin Region mentions that adenosperma rarely occurs in Darwin and has ‘hollow’ stems. As far as I am aware having hollow stems is not a variation, either a species has hollow stems or it doesn’t. All the species of hollow stemmed figs that grow in Australia to my knowledge are consistently hollow.
The Sydney Botanical Gardens collection of adensperma is only small, there were about 5 Australian collections with only one from Litchfield. From first impressions this single collection is very different to the QLD specimens, having broad leaves with distinct raised yellow venation and hollow stems. The leaves of QLD adenosperma are generally narrow, more linear than broad and have solid stems. Hollow stems in one population but not in another leads me think of two possible explanations. 1. The Northern Territory plants are not the same species as the QLD plants or 2. The NT plants have mixed parentage, maybe one of the parents is a hollow stemmed species like hispida – though I doubt hispida is a close enough relative to be able to hybridise with adenosperma. If the NT plants turn out to be a different species that raises the question, which of the populations are truly adenosperma?
The plants in QLD were identified by Berg and or Corner, with an extensive history working with the Figs of Asia, it would seem that the QLD population are correctly identified and the NT plants are incorrectly named. Yet I’m not totally comfortable with that idea. The few adenosperma I saw collected from outside of Australia, appeared to be more like the NT plants, having broader leaves and at least one collection having hollow stems. The illustrations in Berg and Corner also seem more like the NT populations and it is noted that the QLD population are at the extreme end of the variation. So are hollow stems a typical feature of adensperma and the QLD plants are wrongly included in this species, did Berg and Corner somehow forgot to mention this species has hollow stems? Or are the hollow stemmed plants from outside of Australia also potential hybrids with a hollow stemmed species?
Only a month ago I was in Litchfield and high on my list was to find some of these ‘adenosperma’, sadly I ran out of time and missed an opportunity to see living plants, which are much easier to identify than dried collections. Hopefully in the future I can see all the collections of the species and come to a clearer understanding of what is going on!
Berg and Corner 2005 – Flora Malesiana Volume 17 / Part 2, Series 1 – Seed Plants P 353 – 355
D.J. Dixon 2011 – Flora of the Darwin Region Volume 1, Moraceae