That is what it looks like...a baby sword plant.....Sword plants reproduce by sending out runners.
Looks like several are forming. What I do with mine-I will lay a rock on the stem and allow the baby plant to take root-then cut it from the mother plant. Or if you want to move the baby to another tank or location all together-wait until they form roots-then cut the baby from the mother plant.
I had one on my lower rack once that I didn't notice and it went into the tank next to it and rooted...lol....all my tanks are open top....
I just wanted to say - what a lovely, healthy looking plant, you must be doing right by it if it's reproducing. Swords do get rather large, but they're lovely. If yours outgrows the tank completely (they can outgrow a 100 gallon tank, given time) consider selling it or offering a swap for other plants on the forum here, or a local fish forum, people often want mature ones for larger tanks.
Thanks guys! Sorry for my absence on here. Been crazy near the holidays. I haven't seen any roots yet, however, a new shoot seems to now be sprouting from the older new shoot. lol. I will have plenty of amazon sword plantlets if anybody wants them.
It's actually an inflorescence (flower stock) and not a runner. Amazon Swords can do this while submerged a couple times a year but actual flowering depends on the exact species of Echinodorus. The flowers are actually one of the only ways to identify the exact species of sword as even with the same species the leaves are known to take on different sizes and shapes in different people's aquariums.
But, yes, new sword plants will grow on the nodes of the inflorescence and, if you want, you can save them to create all new plants. It should be fine in a 55 gallon. They leaves will probably never break the surface.