Botany on acid

December 31, 2023

As a general rule, soils derived from weathered granite (which dominates the bedrock of Freycinet Peninsula’s peaks and coastline) veer towards being notably acidic. When coupled with shallow soil profiles, interesting things happen – especially to the eyes of a visitor from our verdant, geologically younger islands.

Acidic soil conditions favour the proliferation of heathlands, which are characterised by a diverse array of distinctive Southern Hemisphere ‘heaths’ (epacrids) in many parts of Australia. Tasmania is especially rich in endemic epacrids, with one of their number, Epacris barbata, occurring solely on Freycinet Peninsula and the adjacent Schouten Island.

Having already seen several Epacris species in a range of habitats (as well as another epacrid genus, Richea), I was not focussed on seeing E. barbata whilst walking around Freycinet with my family. Not with the spectacular Xanthorrhoea australis on offer (pictured below and above, at differing stages in their life cycle).

Several species of Xanthorrhoea (commonly known as grass trees) are grown in New Zealand; including X. australis, which we have specified in an upcoming project. Seeing these extremely slow-growing monocotyledons in their natural habitat certainly makes sense of advice that we have received for the successful cultivation – which is to limit the available soil depth for the crown (as well as limiting fertility).

Botany was not the only matter of interest for me as we wandered through Freycinet, with the quality of the granite stonework inevitably drawing my attention. Tasmania is fortunate to have a number of craftspeople currently establishing a remarkable legacy of stonework throughout its parks network – as Logan and I noticed when walking out to Cape Hauy earlier in the year during a work trip.

Returning to the nature of the weathered, acidic, infertile ground on which many plant communities have developed here, I was interested in floristic similarities with acidic, infertile habitats in New Zealand (such as gumlands in the north).

The widespread occurrence of Lepidosperma concavum in dry woodland is reminiscent of the role that Lepidosperma laterale plays within infertile scrub and gumland in northern NZ, and the quantity of orchid species (such as the relatively tall, pink-flowered species pictured below, Dipodium roseum) is another characteristic associated with such environments.

The last word here is saved for a subtle little shrub from the buckthorn family, Rhamnaceae. One look at the helicopter rotor-shaped bracts shown above makes one wonder about the relationship between Spyridium vexilliferum and members of the genus Pomaderris – until one realises that the flowerhead has already finished and retracted into this curious floral structure.