The flowers of Lobelia setacea grow in a panicle of short, branched racemes.

The hairless flowers are blue or violet and white at the base of the larger lips. The flower is two-lipped and five-lobed. The conspicuous larger lip is three-lobed, its spreading lobes obovate, folded along their midribs with obtusely pointed tips. The flower becomes about 15 mm long.

Flowering happens from late spring to mid-autumn (Manning, 2007; Mustart, et al, 1997; Bean and Johns, 2005; Bond and Goldblatt, 1984; iSpot).