What is water celery?

dont know theactual name..it does look like celery but is nice groundcover that flowers in summer..maybe someone else can answer your question better

Here is a link to two water celeries including a variegated one.
I have read that it takes over in a pond situation, not quite considered invasive in that setting, but close.
Otherwise, it looks like Bishop's Weed to me- pleasant enough( until you have it taking over your universe!)

Here is a link that might be useful: Link to Water Celery photos

I think the original post more likely refers to yellowroot - xanthorhiza simplicissima. It does somewhat resemble celery, will grow well in even deep shade and spreads at a modest rate by suckers. Does need more than average moisture.

Wow, that's so pretty. Am going to look for some. Thanks.