Stylidium in Arnherm Land: New Species, Modes of Speciation on the Sandstone Plateau, and Comments on Floral Mimicry

The northeastern portion of Northern Territory, Australia, is known as Arnhem Land. Arnhem Land can be defined in various ways, but the geographical feature I wish to use is the sandstone plateau, often termed the sandstone scarp. Areas very close to the sandstone scarp are also discussed in this paper. The plateau can be said to form a large triangle lying within Oenpelli on the northwest, Nhulunbuy (Gove Peninsula) on the northeast, and Mataranka (south of Katherine) on the south. The borders of the plateau are not easily definable, because isolated tablelands away from the main scarp are numerous in places and because the lower northeastern portions of the plateau may rise only a little above the lowlands. Although cut by dramatic gorges—most notably Katherine Gorge and the gorge of the East Alligator River—the plateau generally lies at only about 300 m (or 1,000 ft). Thus it is not climatically distinct from the lowlands, as are other sandstone plateaus in the world (the Guayana highlands of South America: the mountains of Cape Province, South Africa). Reasons why the Arnhem Land sandstone plateau is nevertheless interesting with respect to speciation in angiosperms are given below.