This has been discussed on Dave's Garden, though not recently. The plant seems to have a zillion variations on the name and it's one of the old, common varieties. When I bought mine, it was labelled 'Joyce Trott'! NOT!!! But I didn't know any better at the time. It was only when I started comparing mine to what a friend had that I began to suspect a problem. Mine was identical to her unknown, but old plant.
The trade seems to market this plant under a bunch of different names but they are likely all the same plant.
This site http://www.mobot.org/gardeninghelp/plan ... ?code=A408
has a good discussion in which they say,
I've also seen discussions that indicate that var. undulata, var. univittata and var. erromena, may all be different stages of the same plant - lots of white, a narrow strip of white and finally all green and that my be born out when you see an old planting of undulata which has turned mostly green.Hosta undulata and Hosta ‘Undulata’ are designations applied to a large number of garden hostas that have in common wavy-margined, twisted leaves, which are either variegated or all green. Hostas sold in commerce as Hosta ‘Undulata Variegata’ or Hosta undulata ‘Variegata’ usually are mounding plants to 15-22” tall featuring narrow oval to elliptic wavy-margined green leaves (to 7” long) with irregular creamy white center stripes. Racemes of funnel-shaped, lavender flowers appear in summer on scapes rising well above the foliage mound to (24-36” tall). The Royal Horticultural Society (RHS) currently breaks down Hosta undulata into four separate varieties (var. albomarginata, var. erromena, var. undulata and var. univittata). Under RHS designation, the within plant is synonymous with Hosta undulata var. undulata. Because of the taxonomic confusion over these wavy-leaved hostas, it may be best to check out the foliage before buying.
Over on the HVX forum, Chris recently identified both of the first two pics I'm going to post as var. univittata.
For my own, (the third pic), I've decided to call it just plain undulata. At times I've called it all of the above except erromena. But mine never goes greener during the summer.
I'd be interested in thoughts from others on the list and also from Chris.