Stems in knots
 

I have a plant looks like a fern. 6inch storks with big leaves it
variegated.
When I brought it the newest Leaf shoot still wrapped up had grown out and
then made a tight 1/4 inch circle in the stem near the leaf . The circle is
vertical the Leaf has not opened. A new Leaf has grown nicely but in the
last two days also done the same thing and not opened yet. Is this a
fertilisation issue. The loops are like pig tails you have on steel stakes
for running rope through.
Thanks