Annual or perennial forb to 1.5m tall, or sprawling to prostrate. Leaves thin or fleshy,. alternating up the stems, hairless, margins entire or toothed, often divided, sometimes with basal segments or lobes. Leaves in the mid-region of the stem 1.5-10cm long. Flowers yellow, with 8-13 'petals'. Flower heads behind the 'petals' bell-shaped, in open groups of 1-20 flower heads at the tops of the stems.
Differs from Senecio spanomerus in that the segments of the leaves are more or less filamentous (length/width ratio of more than 15). The small bracts ('calycular bracteoles') at the very base of the flower head are 1-3mm long, purple or black-tipped, mostly without coarse white hairs. Needs at least a hand lens to see.
The description above is mostly derived from Thompson, I.R., (2005) Taxonomic studies of Australian Senecio (Asteraceae) 5. The S. pinnatifolius/S. lautus complex. Muelleria 21: 49-51, Fig 1d (leaf shape) page 26, Fig. 2c (phyllaries (bracts surrounding the back of the flower head)) page 27, 2e (calycular bracteoles) page 27, Fig 7 (map) page 42, Fig 8 (photo of dried specimen) page 43.
According to this paper, Senecio pinnatifolius var. pinnatifolius occurs well east of the area covered by this key, and the species that occurs in the area is Senecio spanomerus.
The descriptions below do not differentiate Senecio pinnatifolius ssp. pinnatifolius and Senecio spanomerus .
Description and photo (as Senecio lautus ssp. dissectifolius) in G.M. Cunningham, WE Mulham, PL Milthorpe and J H Leigh (1981 and later printings) Plants of Western New South Wales page 676
Flower and spent flower. Australian Plant Image Index, photographer Murray Fagg, Australian National Botanic Gardens, ACT