Plant Identification: Calathea “Bluegrass”

I bought this plant at a botanic garden winter house plant sale. Have never seen it anywhere else. Love it. Bring it inside for the winter (live in Zone 7B) and in summer I use it outside in shade both in pots and in ground. I split each grouping at end of summer; just yesterday I potted up 14 pots–will give some away. It’s a wonderful shade filler and great thriller in pots. Pictures attached.