Eragrostis is a large and widespread genus of plants in the grass family, found in many countries on all inhabited continents and many islands.
Sagittaria is a genus of about 30 species of aquatic plants whose members go by a variety of common names, including arrowhead, duck potato, katniss, "Omodaka" (沢瀉 in Japanese), swamp potato, tule potato, and wapato (or wapatoo).
 Most are native to South, Central, and North America, but there are also some from Europe, Africa, and Asia.
Sagittaria platyphylla, the delta arrowhead, broad-leaf arrowhead or delta duck-potato, is a plant species native to the eastern United States.
 The core of its range extends from central Texas to the Florida Panhandle north to southern Illinois.
 Isolated populations have been reported from Washington State, Missouri, Kansas, Ohio, Kentucky, Pennsylvania, West Virginia, eastern Virginia, North and South Carolina and eastern Georgia, Nuevo León, Michoacán and Panamá.
 It has also become a noxious weed in Australia.
 The plant is an emergent aquatic found in ponds, lakes and slow-moving streams.
Eragrostis australasica, commonly known as Swamp Canegrass, is a tussock grass, in the subfamily Chloridoideae of the Poaceae family, that is endemic to Australia.
 It is a tufted perennial with strongly branched, cane-like culms, that grows up to 2.4 m in height.
 It is typically found on periodically flooded land in arid and semi-arid regions.
Eragrostis infecunda , commonly known as Southern Canegrass, is a species of grass, in the subfamily Chloridoideae of the Poaceae family, that is endemic to Australia.
 It has erect, wiry culms growing to 70 cm in height It is typically found on cracking clay or alluvial sandy loam soils, on floodplains, watercourses and depressions subject to periodic inundation, as well as the margins of marshes and on levees.

Question: Which is found in Australia, Sagittaria or Eragrostis?
Answer: Eragrostis