large-flowered evening primrose
Refers specifically to Oenothera glazioviana, a species of evening primrose with large flowers.
Large-flowered evening primroses were blooming by the roadside.
Refers to evening primrose in general (Oenothera), while オオマツヨイグサ is a specific large-flowered species.
Standard katakana spelling for this plant name.
Kanji spelling is rare; the plant name is usually written in katakana.
From 大 (oo, 'large') + 待宵草 (matsuyoigusa, 'evening primrose'). The katakana spelling is standard for this plant name.