rubral

例句：

1. 1.The rubber tree is a popular ornamental plant in many countries.
   橡胶树是许多国家受欢迎的观赏植物。
2. 2. The red flag fluttered in the wind.
   红旗在风中飘扬。
3. 3. The rubral color of the leaves is a sign of ripeness.
   叶子的赤色是成熟的迹象。