Gentiana, the gentians
Five species, with blue or white flowers.  Only two species can still be found in Delaware.

Gentianopsis crinita, Fringed Gentian
Formerly Gentiana crinita, this is no longer found in Delaware.

Obolaria virginica, Virginia Pennywort

Bartonia virginica, Yellow Screwstem
Bartonia paniculata subsp. paniculata, Twining Bartonia (not shown)
B. paniculata is a rare plant of "white cedar swamps and acidic swampy woods."  The petals are more pointed and the stem leaves are mostly alternate below the inflorescence.

Sabatia, the marsh-pinks
have pink or white flowers with yellow centers.  Five species are found in Delaware.

Centaurium pulchellum, Branching Centaury-plant
This is the only non-native plant in this group.

Sources: The Flora of Delaware, Herbaceous Plants of Maryland.