Drosera petiolaris is a woolly sundew native to tropical Australia. This post describes plants at the type location on the Endeavour River near Cooktown which I observed in June in the early dry season. Similar, closely related taxa are distributed across Cape York and the Northern Territory but their exact relationship to the type is not well understood.
D. petiolaris sensu stricto forms semi-raised rosettes of many leaves around 10cm in diameter. These leaves have a long, thin petiole that has a sparse to moderately dense covering of hairs. The laminae are orbicular. The flowers are borne on a hairy flower stalk. After flowering, the fruit droop downwards on the stalk.
As the water recedes in the dry season, the plants begin to enter dormancy which results in a markedly different phenotype. The new leaves at this stage are extremely hairy and very much reduced in size such that a dense furry tuft is formed at the centre of the rosette. This protective bud insulates the meristem over the dry season until the return of the rains when the plants resume active growth.
At Cooktown, the plants inhabit sparse forest on the seasonally wet banks of the Endeavour River. Plants were observed growing in sandy soils amongst grasses in the bright understory of the open forest.
Drosera petiolaris sensu stricto is known from the Endeavour River and was collected by Banks and Solander during Cook’s original voyage in 1770. As the species comprises a complex of closely related taxa that are difficult to delineate, the true extent of its distribution is currently unknown.
On Cape York there are several similar taxa that don’t exactly match the type. These include a larger plant with thinner petioles around Yarraden and a red swamp-growing taxon that is found in the floodplain of the Jardine River and in seasonally inundated sandplains near Darwin. The lack of readily keyable traits in this group of plants means that these other taxa are accepted under a broader taxonomic concept of ‘D. petiolaris’. In Queensland, the closest formally described relative is Drosera lanata which is distinguished by its very thick covering of woolly hairs on the petioles of actively growing leaves (the hairs of D. petiolaris are sparse).