Ruellia simplex is a plant with a complicated reputation. The petunia-like blooms are a compelling lavender-violet, and they open one at a time, each lasting just one day before dropping cleanly. That brevity barely registers because the plant produces so continuously from summer through fall that bare stems are rarely visible. In warm climates it is evergreen, forming a 3 to 4 foot clump of narrow, glossy, dark green leaves sometimes edged with purple.

The caution here is real: this species is a Category One invasive in Florida, where it colonizes natural areas and displaces native flora through aggressive rhizome spread and explosive seed ejection. Gardeners in frost-free climates should choose sterile cultivars like Purple Showers, which spreads only by rhizome and cannot naturalize by seed. Elsewhere, it is a durable, deer-resistant annual with a genuine tolerance for wet, boggy, or drought-stressed soils alike.