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Alternanthera is a member of the plant species Amaranthaceae. The plant is more commonly known as amaranth. The flowers on the alternanthera are usually tiny — the plant is valued more for its brightly-colored foliage. These versatile herbaceous plants are used not only in gardens and containers, but in aquariums as well.
Most alternanthera are stoloniferous ground covers and spread readily, but should be frequently cut back. This ensures uniform size and bushiness and discourages them from becoming scraggly. They are perennials, but they cannot live in extreme cold. In areas where winters are cold, but not severe, they may survive if well mulched, however.
The alternanthera can make good container plants, but they are mainly planted in outdoor flower gardens. They tend to mix well with annuals, acting as fillers within the landscape. They require moist but well-drained soil, and if planted in full sun, usually produce vividly-colored foliage.
There are several species of alternanthera that are common additions to aquariums and water gardens. The most striking of these may be the alternanthera reineckii (A. reineckii). Varieties of this species have purple, pink or red foliage. They require bright light to do well, but can be difficult to grow. A. reineckii can be propagated by nipping off the top part of the plant and placing it in the bottom of the aquarium. This not only increases the number of plants, but may improve the original by encouraging growth.
Other species of alternanthera can be grown in aquariums, but may be harder to maintain. For example, A. bettzichiana and A. sessilis are beautiful aquatic plants, but they can be fussy. A slightly acidic ph and soft water are necessary for these types of plants to thrive in aquariums. They have very particular needs regarding fertilizing and light as well.
Most species of alternanthera are easily propagated. Cuttings and root divisions often grow quickly with little effort. They should be planted into a sandy potting medium and kept moist until well rooted.
One species of aquatic alternanthera should be used with caution. A. philoxeroides, also known as alligator weed, has been named a noxious weed in the southeastern United States. While they may be acceptable to use as freshwater aquarium plants, they should not be planted outdoors. Alligator weed is highly invasive and forms a thick mat that prevents drainage from waterways and causes flooding.
Alligator weed is currently being controlled in the US through biological methods. The alligator flea beetle, alligator weed stem borer and alligator weed thrip are all being utilized to help deter the growth of this rapidly growing plant.