The Alternanthera reineckii 'Mini' is an nice red plant that can grow up to +- 35 - 40 centimeters.
Azolla filiculoides (previously called Azolla caroliniana) from North America is a small (1-2 cm tall), floating fern. A decorative plant for open aquariums.
Bacopa caroliniana originates from US, stems become 10-30 cm long and 3-4 cm wide. Apart from relatively good light it makes few demands.
Christmas moss (Vesicularia montagnei) is a kind moss which forms many side-branches. This moss is excellent for binding on wood or stone but can also be used loose. 100% safe from an in vitro cup.