Changing plant

I found this in my tank, the original plant had 3 leaves per node and when i cut it in half i found that the top half continued to grow with 3 leaves per node but the bottom half's new growth has 2 leaves per node. here is a picture of the bottom half with 3 leaves per node, unfortunatley the top bit is unclear, it has 2 leaves per node, the new leaves grow at 90 degrees to the ones on the node below.

I'm realy curious to know why it does this cause i always thought that leaf count per node is one of the ways species can be described

 

:bigsmile::bigsmile::bigsmile:bump bump:bigsmile::bigsmile::bigsmile: