The members of the Alismataceae family of flowering plants are also known as Amazon sword plants. They are distributed from the United States to Argentina.
Within the genus, there are plants that live for more than two years (perennial) and some that finish their cycle within one year. Echinodorus plants are marsh and bog by nature, meaning that they are semi-aquatic and mostly monocots. They can grow submersed, immersed or with their leaves floating on soft wetlands. They prefer regions with a tropical climate, soil rich with nutrients and good light. In terms of plant anatomy, this genus shows tremendous diversity. Flowers are bisexual with white petals and linear filaments. Some of them have pedicels (a branch or a stalk that attaches flowers to the inflorescence) and others are subsessile. Leaves are petiolate or sessile with various shapes from oval and linear to lanceolate. Fruits can be flattened, but more often they are longitudinally ribbed. Propagation is done by division or by new plants, developing on submerged flowering stems. If they grow above the surface (emersed), propagation can be done by growing seeds in moist and warm conditions. 
Echinodorus cordifolius, known as the mud king, elephant’s ear or spade leaf sword is the perfect addition to any aquarium. With its enduring nature and appealing leaf shape steals attention even from the least interested passers. It was first described in 1753 and classified as part of the Echinodorus genus in 1857. Its natural habitat are ponds, marches and swamps in several southeastern states, South America and Mexico. It is never a good idea to collect plants from the wild since it can endanger the health of all your aquarium species.
The most distinguished characteristic of this plant is that it grows vertically first and then becomes horizontal by bending over. In favorable conditions, the mud king will naturally grow above water level. Regular pruning and less illumination will keep him in submersed state. Submersed plants have large bright green leaves and emersed have robust and dark ones. The mud king tolerates a wide range of pH levels and temperatures but requires additional plant feed and excellent mixture od clay and peat.
- cordifolius can be grown outside by ponds in states with no frost. Flowers in late summer and early fall, producing enormous white flowers. The only concern is that sometimes it can be attacked by insects.
There are several varieties of Echinodorus cordifolius offered on the market and it’s best to gather additional information in order to make the right choice for your aquarium. Echinodorus cordifolius “gelb” now known as Aureus is neither easy to grow or cheap. Ovalis is the best variety for small aquariums. Originally cultivated in Singapore, the Marble Queen has the most attractive foliage. With a strong light, additional CO2 and proper substrate, its leaves show spectacular marbling effect. 
Another commercially used specie is Echinodorus bleheri sold under the name “Paniculatus”. Originating from South America, this is the perfect easy-growing plant for beginners. All it needs is a nutritious bottom and brightly illuminated aquarium.