noun
long-day plant
Botanical term for a plant that flowers when the day length exceeds a certain critical duration, typically in late spring or early summer.
ホウレンソウは長日植物で、日が長くなると花が咲きます。
Spinach is a long-day plant; it flowers when the days get longer.
Compound of 長日 (long day) + 植物 (plant), a calque of the English botanical term 'long-day plant'.