Rainforest tree named not for Davidson of plum fame

Some plant groups seem to have their stronghold in southern Asia, with a tentative dip into the warm tropics of north-eastern Australia. There origins can be different but they are mostly assumed to relictual in Australia, living in rainforest that once covered larger areas of Australia when it was wetter and hotter in geological time, and less intensively inhabited in more recent times.

Davidson's Alder, Spiraeanthemum davidsonii, was first collected from the 'highest crest of Mount Bellenden-Ker', the highest peak in Queensland. Ferdinand von Mueller described it in 1887, in The Australasian Journal of Pharmacy no less.

The genus Spiraeanthemum occurs naturally in Papua New Guinea and islands to the east of there, with this one species in growing in Australia, between Mount Spurgeon and Innisfail. 

Davidson's Alder is quite different to the other species of Spiraeanthemum and was for a time moved into an allied genus, Acshmithia. A molecular study published in 2020 confirmed its placement in Spiraeanthemum but it does differ from other species in that genus in having a large terminal cluster of flowers and sometimes strongly toothed leaves.

The small white flowers are very dainty, and very pretty, with their fine stamens bursting out from within papery petals. 

In mature form it has been described as a coppicing, 'poorly formed tree'. The plants photographed here were growing in the nursery at Cranbourne Gardens, and like the plant featured in my post a fortnight ago, propagated from material collected on a joint collecting trip to far north Queensland with James Cook University in Townsville and other partners.

The species is not named after the same Davidson as the Davidson's Plum (species of Davidsonia) which honours a Queensland sugarcane grower, J.E. Davidson. In this case it's Alexander Davidson who collected with W.A. Sayer, who was commissioned by Mueller to collect plants from the far north. The two of them also found Rhododendron lochae in the Bellenden Ker ranges.

As to what kind of plant this is, given you are unlikely to see it in cultivation, it's in the family Cunoniaceae, which also includes Coachwood and New South Wales Christmas Bush (Ceratopetalum), Black Wattle (not an Acacia, but Callicoma serratifolia) and the wiry Bauera. 

The family is mostly from the southern hemisphere with a distribution a little broader than the genus Spiraeanthemum, extending north into Malaysia and across the pacific to the Americas. Most Cunoniaceae grow in tropical and wet temperate forests.  

All members of this family have a scale-like leaf, a stipule, between where the pair or whorl of leaves are attached to the stem. In this case the stipule is an elongate hairy appendage, as seen here. It falls off as the stem matures.

An unusual plant, and one that may be under threat from climate change. That's why we've included in our collection at Royal Botanic Gardens Victoria, part of a distribute insurance policy across Australia.