This is where the segment's edges are either lighter or darker than the segment. The flower is round having a full appearance. The sepals recurve to make three flat sides while long petals extend into modified points. The flower has extra petals lying on or above the normal three petals. All plants have a basic complement of chromosomes.
Most plants are diploid which means they have two identical sets of chromosomes in each cell.
Tetraploids have four sets of chromosomes. A diploid cannot be crossed with a tetraploid for hybridizing. Some believe that a tetraploid daylily is a stronger plant with larger flowers. However, when looking at many plants available today, there are as many good looking diploid daylilies as there are tetraploid. I believe the most important determining factor is what you like best.