There are a couple that this brings to mind one is 'Flowing Fountains Cast Iron Plant , an Aspidistra. There are a zillion cast Iron plants. There are also some close relatives like Rohdea japonica. There are sever Roddea. I have only grown the old fashioned pass along cast Iron. Yours seems fleshier and lighter in tone which could be environmental since I am growing it on thin soil , un irrigated in Central Texas. It would like a richer more mesic soil.

Neither aspidistra nor rohdea are cold tolerant enough to produce a clump that size in zone 5 CO :-) My guess would be the colchicum as well. But hard to confirm unless you dig one up or wait for the flowering

It could be a bletilla

nel5397, bletilla does look very similar. Interestingly I've been wanting some bletilla. I have this idea to go back to the house where I saw it in a couple of weeks and see if it it got a bloom. Although it may have already bloomed, but if it did, someone was very good at cleaning up scapes. Because there was no sign of a bloom or bloom stalk. I should have just asked for a piece of it while I was there! Darn.

Colchicum also. Not Bletilla.

Colchicum. It would have bloomed last autumn (8 months ago) and - except in those instances where seed capsules might follow - there isn't that much material left behind afterward. Because the flowers come directly from the bulbs, without any additional branches or stalks being involved.

Oh yeah that Colchicum does seem to be a match also! Thank you.