I haven't seen this before. Usually such an event might occur when a vein on the leaf has been cut. Then with the humdity the leaf puts up babies. That may explain this though I don't see any cuts on your leaf. But, I do know that chirita leaves really have a super capacity for propagation. I love to put down leaves to see the babies come up. Last summer I started cutting the leaves into two halves, the top and bottom. I grew excellent babies from both halves, and actually, the top half made a bigger baby than the bottom. But, now with a few more leaves under my belt I am finding that I get good babies from both halves depending on unknown factors--such as size and health of the leaf part. However, now I am all about experimenting, and am trying new methods. On one leaf I cut it lengthwise down the midrib and am rooting two pieces that way, with a tiny leaf tip cutting as well. So, far no plantlets but they have made roots. And, I am also cutting my leaves into three cuttings--one with the petiole and just a bit of the bottom of the blade. The second one above that and the third cutting from the top half of the leaf. I just checked yesterday and saw that the petiole cutting with a bit of blade has rooted. I did some others from a plant that had very long petioles, so I cut those in two. So far, the bottom cuttings, which are nothing more than an inch or so of petiole have not rooted but its only been about three weeks. I am sure there are other ways to propagate a chirita leaf. Hey, I just thought of another way. Put the leaf down flat over perlite/vermiculite, but cut slash cuts across the leaf veins, leaving the leaf intact but a bit slitty. Perhaps the leaf will do plantlets like yours.

Jon