Monday, January 2, 2012

The world's largest form of Drosera binata


Could this be the biggest form of Drosera binata in existance?

Drosera binata, the forked sundew, is grown all around the world and highly prized for its magnificent and unusual foliage. Here is a photo of the most commonly grown clone, D. binata var. binata or the “T form”. I took this photo in Cradle Mountain National Park, Tasmania. It was growing in sunny heathland dominated by grasses, most commonly on the eastern shore of Dove Lake (photo below at right). This plant was no more than 15 cm high and usually had a Y-shaped leaf, with occasional plants having a third leaf branch.

binata_T_form binata_T_form_habitat

Another form of this plant I am familiar with occurs more than 2000 kilometres further north, nearly at the northernmost limit of its range in Queensland. This plant is usually referred to as D. binata var. mulifida form “extrema” because the narrow leaf blades are divided as many as 100 times - more than in any other form. Plants of this variety in cultivation seem to have originated from Stradbroke Island just to the east of Brisbane, although similar plants form also occur further south in northern New South Wales (at least as far south as Coffs Harbour) and further north (at least to Tin Can Bay and Fraser Island). That said, I think the Sunshine Coast clone I am familiar with is actually something entirely different again, as we shall see…


Here is the habitat of the clone from the Sunshine Coast. It is quite different from the Tasmanian habitat. Although also heathland, it is dominated by a fern with highly divided leaves that grows in hummocks that extend over hundreds of square metres and can reach nearly 2 metres tall. Here is a close up of this fern’s fronds.


I’ll let the photos next photos speak for themselves. This is a closer view of part of this hummock. Can you see the sundew? Hint: its to the upper right of this photo. The height of this hummock starts about 1.5 metres off the ground, increasing to well over 1.8 metres further back.


And a bit closer again…


The spreading leaves of this sundew seem to serve two purposes. First, the branches allow its weight to be borne evenly across several ferns, allowing it to effectively float over the top of the hummocks. Second, they act like a spider’s web, capturing insects as they walk across the top of the ferns’ fronds.


Here is the larger leaf raised to its full height – well above the top of the fern’s fronds. To give some sense of scale here, I am some 1.75 metres tall – nearly 6 feet. THESE LEAVES ARE WELL OVER ONE METRE (3 FEET) LONG!!! I took the last two photos standing up, holding my arm comfortably out at shoulder height.


Like other forms of Drosera binata, this giant form spreads from roots to form clusters of individual plants. Unlike other clones, the roots extend a long way underground – plants I have seen dug up by housing development excavations nearby had their root systems deeper than 10 cm under the surface. The growing point rises to the surface on a relatively thick stem. This feature allows these plants to survive bushfires and some man-made disturbance, such as mowing. Once, in Mooloolah National park, I saw dense thickets of this plant growing in recently burned areas. I have also been told of similar occurrences on Fraser Island further north.



When it grows in disturbed habitat, this plant tends to be shorter and have more upright petioles. As surrounding vegetation grows back, the petiole height increases accordingly. However, I have only ever seen permanent populations of this plant growing with this fern – other vegetation seems to outcompete it. Also growing at this site were the ubiquitous Drosera spathulata (probably var. gympiensis).


Sadly, this most spectacular form of D. binata now seems to have been extirpated from everywhere except a few isolated parts of the Mooloola National Park, and a rapidly decreasing number of sites in the Mooloola River catchment. Other populations at Mountain Creek and Mooloolaba (including those figured in Vol. 3 of Allen Lowrie’s works) are now under school playing fields (Mountain Creek), or housing (Mooloolaba), or due to changing soil chemistry (both Mountain Creek and Mooloolaba). This is sad, as I believe plants further north at Tin Can Bay and on Fraser Island are entirely different, because they lack the specialist growth of this form. Plants from nearby Bribie and Stradbroke Islands seem even different again – they are shorter and grow in different habitat types. Further south, it is more generalist in coastal heathland, before being replaced by smaller plants in the Sydney basin and in Victoria. Hopefully, the last vestiges of this spectacular plant will be managed in a way appropriate for its long-term survival.