Hi Lin, I may have ID'd the plant.
As the plant is very widespread, the flower & leaf form, and size of the plant change from place to place. In Hawai'i the leaves may be wider or thinner, flower petals may or may not overlap a bit, all on wild plants.
The flowers must contain 5 sepals, 5 petals, and 5 stamens.
The characters in this link help to ID the species.
http://ntsavanna.com/elm-leave...
