Sagittaria platyphylla

Easy arrowhead from the south-eastern USA that forms a rosette of strap-like underwater leaves (up to about 50 cm) and spreads by runners. It is an invasive weed where it escapes, so never release it.

Check your local laws. Australia: Weed of National Significance. Queensland: category 3 restricted invasive plant (must not be given away, sold or released). NSW: Class 5 restricted weed, must not be sold, bought or knowingly distributed (state-wide). SA: declared (as S. graminea). Tasmania: import and sale prohibited (as S. graminea). WA: P1 (no trade, sale or movement into the state) and P2 (eradicate). NZ: Unwanted Organism (MPI) and National Pest Plant Accord species. It cannot be sold, propagated or distributed anywhere in New Zealand. Never throw it into ponds, rivers or drains.