Annual forb to 80cm tall. Leaves alternating up the stems. Leaves in the mid-region of the stems mostly 3-12cm long, usually divided, sometimes narrow and flat, margins entire or toothed. Flowers with about 8 yellow 'petals'. Flower heads broad hemispherical, in groups of 3-12 at the tops of the stems. Usually occurs on the margins of lakes and swamps.
PlantNET description with photo of dried specimen: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Senecio~lacustrinus
Key (page 29), description (pages 68, 70, 72), and photo of dried specimen (Fig. 21 page 71) in IR Thompson (2005) "Taxonomic Studies of Australian Senecio (Asteraceae): 5. The S. pinnatifolius/S. lautus complex" Muelleria 21: 23-76