It’s a crinum!
Back in the 90s, a friend who was quite a scavenger had rescued plants from an old yard. I don’t know what the plans were for the yard, but the old bulbs and shrubs had to go.
She also ended up with a huge bulb mass that she carted around to various nurseries, trying to find out what it was. This was back before most people had access to the internet, but one place did say they thought it was in the amaryllis famil.
When she split it up, she gave some to us, though we weren’t sure what we would get out of it.
We got crinums.
Crinums are a southern classic and a favorite passalong plant, according to The Southern Living Garden Book. Seldom seen in newer housing areas, they are now found in old home site, country gardens and in cemeteries. Needing little care, “they tolerate adversity so well that some say no crinum has ever died.”
Old bulbs may weigh as much as 40 pounds. They should be divided infrequently as, once disturbed, they may not bloom the first year after planting.
I don’t think you’ll be able to find these at many home supply centers or garden centers.