Ruellia noctiflora, the nightflowering wild petunia, is a herbaceous perennial found along the Gulf coast. Both its specific and common names derive from its habit of nocturnal flowering. In spite of the common name it is in a different family from the garden petunia.
It is considered endangered in Florida.
The plant grows to 16inches[1] with oval, pointed, usually stalkless leaves up to 2.8inches long borne in pairs on thin, hairy, purplish stems. It bears white, trumpet-shaped, five-petalled flowers 3inches long and 4inches across; these open at night and fall by mid-morning, and are pollinated by hawk moths, whose long proboscises allow them to reach the nectar held at the base of the flower.[1] The resulting fruit is a capsule 0.8inches long with the long style retained, resting among the five long spikey sepals. When ripe it splits in half longitudinally, discharging the seed. Unusually for the genus no cleistogamous flowers are formed.[2]
R. noctiflora is generally a wetlands plant and prefers longleaf pine savanna. The principal threats to it (besides outright habitat destruction) are suppression of the fires needed to clear out the understory, and competition from invasive species, particularly cogon grass.[3]
Hybridization studies with other North American Ruellia species suggest a close relationship with Ruellia caroliniensis, which grows across the United States southeast.[4]