As Wikipedia says (https://en.wikipedia.org/wiki/Non-vascular_plant):
Consequently, phyllids are unable to control the rate of water loss from their tissues and are said to be poikilohydric.
And indeed, if you've touched these types of plants, they can feel wet and sometimes even slimy. Sometimes the liquid leaking out can look like dew drops, too.
Is there a proper term for this fluid? I thought sap at first, but it seems that term is reserved for vascular plants.