There are nearly 30 species of native primrose willows in Florida and they are a very diverse genus in terms of growth form and preferred habitat. This makes field identification a bit tricky for some. Narrow-leaved primrose willow (Ludwigia linearis) is relatively easy to identify as it is a relatively diminutive upright species with decidedly narrow leaves. It is common to open moist to wet habitats throughout much of the Panhandle and then south to the upper two-thirds of the peninsula. It also is found throughout much of the Southeast Coastal Plain from east Texas to New Jersey.
Narrow-leaved primrosewillow is a perennial that dies back to the ground in winter and reemerges in early spring. The thin stems can reach a mature height of 3 feet by summer. Individual plants can produce up to 3 stems each. The stems tend to be reddish in color and smooth. The thin leaves alternate on the stem and are 1-3 inches long with entire leaf margins.
Flowering occurs in the summer months. Each bloom is comprised of 4 bright yellow rounded petals and is about 1 inch across. They are sessile to the stems and this is a key field identification feature along with the leaves. Flowers are pollinated mostly by bees and the ripened seed capsules are smooth and noticeably 4-sided.
This is a rather nondescript member of the genus and not offered for sale commercially as far as I know. It would be easy to grow from seed collected after the capsules turn brown and begin to split. Otherwise, simply enjoy it when exploring moist areas in much of the state.