Water Primrose

Family: 
Onagraceae (evening primroses)
Description: 

A common shoreline plant with bright yellow flowers usually having 5 petals. Blooms May–October. Stems long, trailing, creeping out across the water’s surface, can reroot from cuttings. Leaves shiny, dark green, alternate, variously shaped from oval to narrow and willowlike. Roots are of two types: typical roots that grow downward and take nutrients from the soil, and “air roots” or “breathing roots” that are white, spongy, grow upward, and float—these apparently absorb gases from the air.

Similar species: There are 11 species of Ludwigia in Missouri, which all have 4 petals or, lacking petals, 4 sepals (not 5).

Habitat and conservation: 
Grows in dense mats in the shallow areas of ponds, lakes, and streams.
Distribution in Missouri: 
Statewide.
Human connections: 
When this species grows too rampantly in fishing ponds and waterways, it can become a nuisance and require control. People have introduced this plant all over the world, where it can become a noxious weed.
Ecosystem connections: 
Colonies of aquatic plants are important nurseries for fish and other aquatic life, providing sustenance and shelter and for the small creatures at the base of aquatic food chains.