Doesn't really look like either.......
If it is definitely no other possibilities, than those two - my money would be on the 'Monte Carlo'.......... but it really does not look right.
- No offence meant, but is this by any possibility something, you got from a local pond??
I was wondering that, Callitriche sp? It looks like it might be Callitriche "stagnalis", which is <"pretty much cosmopolitan">, so may occur on Mauritius. Another option might be Callitriche deflexa, but that isn't a plant I'm familiar with.
The scientific name of Hc "Cuba" is "Hemianthus callitrichoides" which means that it is described as a Hemianthus sp. that resembles a Callitriche. Without a flower a lot of little aquatic plants just look fairly similar.