圆叶平灰藓（学名：Platyhypnidium riparioides）为柳叶藓科平灰藓属下的一个种。

Platyhypnidium riparioides, the long-beaked water feathermoss, is a species of aquatic moss commonly found in many regions. This species is among the largest aquatic mosses growing up to 15 cm long. P. riparioides grows in a procumbent or pendulous fashion along rocks and tree roots and may form extensive lax mats of many intermingled plants. It is widely distributed South of the Arctic and can grow abundantly in suitable areas.