reed

The reed is a common water plant that grows at the shoreline whereas the flag plant grows completely underwater. Both are tall, fragile, aquatic grasses that provide a covering to anyone hidden within it. These similarities are why translators often get the two mixed up.

Reeds are hollow and can be used as writing pens or corrective rods once dried. 

Symbolically, these plants are referred to for their movements in the wind and water as being fragile as opposed to firm in their standing.