Over here they sell both Echinodorus tenellus and Lilaeopsis sp as "micro sword". If it's Echinodorus (grows in a distinct "rosette" shape, may have a slight tint of pink on the leaves), it'll carpet fast and become basically a weed that you need to constantly prune (assuming it likes the light/co2/nutrient environment). If it's Lilaeopsis (thinner leaves, tend to grow straight upwards), it'll grow a bit slowly, and won't really form a lawn/carpet effect without strong light. On the other hand, a dense Lilaeopsis lawn is amazingly beautiful if you can grow one.