I have no idea if what my Kleiner Bär - Jungle star does is universal for all Echinodorus spp. But this one did the same one day, sticking leaves up above the water surface. The sticking out tips since it is submersed grow form dries out within a day or 2 and turns brown.. It's emersed grow form is lancet leaf hence the name sword i guess, But in a way this plant senses it's invironment, leaves reaching aerial CO² triggered this plant to shoot out emersed formed leafstalks with more obovate leaf forms that grow more oval while they mature. It completely stoped making submersed sword leaves. This din't take very long, to completely turn into a rosette in the substrate with only leaf stalks submersed and emersed form leaves. I also notice that this plant even after growing for almost 3 years now a little deeper than 20 cm water it, never made a submersed form runner. I actualy have no idea if Echinodorus spreads with runners submersed. Probably not, at least not in this condition.
Whit sensing it's invironment, i did grow on some plantlets from it's flower stalks in pots emersed. So it doesn't stand in water. These plantsdo not make such long leaf stalks. They stay significantly shorter. While the one standing in deeper water shoots out 20 cm long leafstalks with a tiny leaf that only grows bigger once it reached over the surface, growing into a bigger leaf on a 40 cm leafstalk.
Remarkable actualy that this plant absolutely is aware of it's conditions, knows what to do and grows accordingly. Definitively a plant that made me think completely different about plants in general. All tho they doen't posess a brain, they still kinda posseses a form of intelligents. So inteligents doesn't reside in a skulls brain cell only.
Anyway i've seen pictures of several Echinodorus spp. growing in the same fasion. So i assume it likely goes for all of them. Nice is te are also vigorous flowerers, mine makes one flower stalk after another all year long. On these flower stalks new plantlets will grow, starting at the tip of the stalk. If the tank is big enough the flower stalk will bend over and the plantlet touch the water. Than it will strat growing roots. Cut this plantlet off and plant it as seperate plant again in front of it's mother. It will transition into submersed growth and form lancete leafs again. Even beter if all flowers on the flowerstalk are done flowering, than cut it off at the base and leave the stalk floating in te water. This will trigger each seperate flower bunch on the stalk to grow a new plantlet.
Than you can create best of both worlds virtualy for free. A big emersed mother surrounded by a bunch of here babies in submerded form.