Identifying a Night-Blooming Perennial: Oenothera triloba

A Low, Spreading Evening Primrose Relative

The plant described—foot-wide clump, dandelion-like leaves, 1-inch white/yellow flowers opening rapidly at 6–7 PM, perennial, spreading—matches Oenothera triloba (stemless evening primrose).

Key Traits

• Native to central/eastern U.S., not Ireland/Holland (though seeds may have traveled).
• Low rosette, deeply lobed leaves.
• Flowers open in minutes at dusk, wither by morning.
• Spreads by seed and short rhizomes.

Confirmation

Compare with this reference. If it matches, you have a lovely, fragrant native for dry, sunny spots.