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Senecio

1. Heads with conspicuous rays clearly exceeding the involucre.

S. vernalis

1. Heads with rays minute (barely equalling involucre) or none.

2. Leaves and stems densely glandular pubescent; bracteoles at base of involucre (2–) 2.5–5.5 mm long.

S. viscosus

2. Leaves and stems glabrate to densely pubescent, but glandular hairs absent or sparse; bracteoles at base of involucre 0.9–2.6 mm long.

3. Rays present but minute, barely equalling involucral bracts; plant densely pubescent, with glandular hairs sometimes present but sparse; bracteoles at base of involucre and involucral bracts usually with greenish tips, rarely dark-tipped.

S. sylvaticus

3. Rays none; plant glabrate to somewhat tomentose, but without glandular-viscid hairs; bracteoles at base of involucre (at least some of them), and often involucral bracts greenish with conspicuous blackish tips. 

S. vulgaris

All species found in Senecio

Senecio sylvaticusWOODLAND RAGWORT 
Senecio vernalisEASTERN GROUNDSEL 
Senecio viscosusSTICKY RAGWORT 
Senecio vulgarisCOMMON GROUNDSEL 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. June 22, 2018. https://www.michiganflora.net/genus.aspx?id=Senecio.