Bleeding Heart Family: Herbaceous plants. The 4 petals are irregularly shaped and sized, either to look like hearts or spurred sacs. The leaves are parsley-like, but with rounded edges and a blue-green tinge.
Caper Family: Herbaceous plants. Flowers mustard-like. Four yellow petals. Ovary is banana-shaped. Leaves mostly compound palmate.
Dogwood Family: Small to large woody shrubs. 4 large white showy bracts which may be mistaken as petals. These white bracts surround a tiny yellow cluster of flowers. Leaves opposite. Dogwoods may be trees or small ground covers.Evening-primrose Family: Herbaceous plants. There are 4 of each of the petals, sepals, and stamens. The style (long projection from the central ovary has a 4-part cross (X) at its end, or is bulb-like.
Gentian Family: Annual or perennial herbs with glabrous herbage and simple, opposite or whorled leaves. Flowers showy and tubular or funnel-shaped with 4-5 lobes.
Hydrangea Family: Trees, shrubs or vines with simple opposite leaves without stipules. Flowers perfect and regular with 4, 6 or 10 petals. The ovary is inferior.
Loosestrife Family:Mustard Family: Herbaceous plants. Urn-like flowers with 4 petals shaped as an cross or an X when viewed from above. The flowers have 6 stamens (4 above, 2 below).
Oleaster Family: Deciduous shrubs or trees with opposite to alternate leaves and small, inconspicuous flowers either solitary or clustered at the nodes. The flowers may either be perfect or unisexual. If the latter, the sexes are on separate plants.
Plantain Family: Herbaceous plants. Small brown or green flowers on erect leafless stalk. The leaves are basal and appear to have parallel leaf veins. Some taxa in this family appear to be 4-petalled, but they are 5-petalled because they have a large petal that is the result of 2 merged petals.
Poppy Family: Herbaceous plants. Four large, colorful, showy petals. Poppies have many stamens surrounding a swollen central ovary. The sepals fall off the flower as it opens.
Mountain Lover, Oregon Boxwood: Paxistima myrsinites (Synonyms: Pachistima myrsinites, Pachystima myrsinites): Woody shrubs with opposite leaves and minute deciduous stipules. Flowers perfect, small and inconspicuous.
Teasel Family: Herbaceous, weedy biennials or perennials. flowers in compact flower heads. Corollas irregular with 4 lobes. 4 stamens.