In profile the flower of Viola decumbens looks like this. It appears as if this flower had grown at a stem tip or it has a leaf pair on its stalk. The top part of the stalk is dark red and curved, allowing the flower to nod.
Long calyx lobes are visible. The lower petal is shorter than the others (Manning, 2007; Privett and Lutzeyer, 2010; JSTOR; iSpot).