The ironroot has gained one main bonus. It's ability to grow roots. Because of this, it can feed a lot longer on the same spot, as opposed to just a small patch. The rest still works the same. Due to magnetism small iron bits get attracted to the plant, the iron gets sucked out, and the rock attached falls. The root however has evolved greatly. Instead of a small anchor point that sucks out a small patch of iron, then floats away to the next, the anchor points grew as roots. Because of this, they did not need to float away. They could just simply grow longer roots.
As opposed to their reproduction, they have something totally different. Every 6 months, a small ball grows on the tip of the ironroot. This continues growing for 2 weeks. Then it gets detached. The cellball, which is ctually just a kind of egg with a small rootless Ironroot in it, floats with the current until it touches the surface, at which the cellball membrane pops open and releases the ironroot. This ironroot will float until it can anchor itself to the ground, and start growing roots.