In article ,
says...

I have been digging up lots of Ophiopogon (black grassy-leaved lily)
which has been long established and beginning to take over other plants.
As I dug out the very deep roots, I found very many nodule-like pods
along the length of the root mass. If these behave as nitrogen-fixing
organs and can be safely left in the soil, then I'm not too worried.
However, if they all turn into masses of Ophiopogon plants and start to
take over the world, I shall be deeply concerned. Does anyone on urg
have experience with this plant? I would be really grateful for any advice.

http://stories.rbge.org.uk/archives/tag/ophiopogon

says that the nodules retain water to survive drought.

I have patiently nurtured a large dense patch of ophiopogon
nigrescens, 3 or 4 ft across, grown as weed-beating ground cover beneath
Cercis canadensis 'Forest Pansy". In fact it's such a great ground cover
I'm trying it under a purple elder and under persicaria red dragon. I
don't find it hard to control so don't think you need worry about it
taking over the world :-)

Janet