Crinkled giant val

I have a stand of giant val in one corner of my tank.  Of the dozen or so
individual plants, all but one are completely normal.  The leaves of the
other plant are pleated like an accordion for their entire length:

  / /
  \ \
  / /

Any idea what might have caused this?  It's really very attractive, and
it's much shorter than its neighbors, which suits me just fine.  All the
plants in the stand are derived from a single parent plant, so it's not a
case of mistaken identity.
Kevin Conlin   Montreal, PQ, Canada   "We're Canadians.  We HAVE to be polite"