季节二态

Seasonal \Sea"son*al\, a.
1. Of or pertaining to the seasons.

2. Occurring or being used in a specific season; as, seasonal
items for sale.

{Seasonal dimorphism} (Zo["o]l.), the condition of having two
distinct varieties which appear at different seasons, as
certain species of butterflies in which the spring brood
differs from the summer or autumnal brood.