I have often noticed that edible species of Portulacaceae are common around ancient indigenous sites. The tubers (and leaves/flowers) of these species are edible and reputedly quite tasty. Most of the species are so small that they would hardly qualify as a meal on their own. However, we need to consider that drought and widespread bushfires can make for "slim pickings" in the Australian bush. During such times any edible vegetable would have come on to the menu. Species of Portulacaceae are more resilient to drought than non-succulent herbs and grasses, and they frequently occur on bare, rocky, elevated areas that are less prone to the ravages of fire.
The activities of humans may have helped to distribute many species of plants. There is some speculation that Tetragonia tetragonioides ("Warrigal Greens" or "New Zealand Spinach") may be more common today around ancient indigenous campsites and along the old bush trails. There is little doubt that Aboriginal people collected all manner of bush foods which they brought together at the campsites.
Seed would have invariably fallen off and become more concentrated in those areas. It is also possible that plants that were used in traditional medicines and ceremonies may show a greater concentration around campsites and ceremonial grounds.
Locally I know of several ceremonial "bora" grounds where the tuberous species Grahamia australiana, Portulaca bicolor and P. australis are very
common. Further west I have found those same species, as well as the tuberous Calandrinia pleiopetala sens. lat. in similar high concentrations around the old campsites. In the central west of southern Queensland I have found Grahamia australiana to be locally abundant around ancient Aboriginal rock wells and hearths.
The occurrences may be purely coincidental, given that bare, elevated areas with stony, skeletal or sandy soils are also typically the preferred habitat of Portulacaceae species. However the concentration of species around ancient indigenous sites does suggest to me that indigenous activities may have been a major contributing factor in the distribution of some species. Over many thousands of years, human activities may even account for the widespread distribution of some species today. Grahamia australiana (syn. Anacampseros australiana) for instance, has an extremely large range of distribution, from Cape York in Queensland to the Flinders Ranges in South Australia. It is highly likely that many of the ancient extensions in its distribution can be attributed to human trade and the periodic migration of peoples about the landscape. Food for thought!
