Alternanthera reineckii 'Rot' ('Red')

Geographical Origin and Habitat: Alternanthera reineckii 'Rot' (commonly known as Red Temple Plant) is native to the tropical and subtropical areas of South America, distributed mainly in Brazil, Argentina, Paraguay, and Uruguay. In the wild, it colonizes floodplains, muddy riverbanks, and shallow ponds exposed to direct sunlight. It grows easily as an emersed marsh plant during the dry season and as a submerged plant during seasonal flooding, absorbing large amounts of organic nutrients from warm, calm waters.

Taxonomy & Genetics: It belongs to the Amaranthaceae family and the genus Alternanthera. The cultivar 'Rot' (or 'Red') represents one of the most classic and popular horticultural selections in the aquarium hobby due to the stability and intensity of its red foliage. Genetically, this variety is characterized by high synthesis of anthocyanins, pigments that act as a protective screen against direct sunlight and UV radiation in its natural habitat, resulting in spectacular red shades in the aquarium.

Physical Structure: It is an erect stem plant with fleshy, sturdy, and well-branched stems that reach a height of about 40 cm and a foliage spread of 15-20 cm in the aquarium. The leaves are arranged in opposite, decussate pairs along the stem. They are lanceolate-ovate, slightly pointed at the tip, and have finely wavy margins. It develops significant adventitious roots both from the main root system and along the submerged nodes.

Color & Texture: The outstanding feature of this cultivar is its intense coloration: the upper side of the leaves assumes tones ranging from bronze-red to dark brownish-red, while the underside shines with a very deep and saturated purple-red or fuchsia. The leaf texture is smooth and slightly glossy underwater, with a firm consistency that allows it to maintain its shape in moderate currents.

Lighting & CO2: It requires moderate to intense lighting to stimulate photosynthesis and preserve the deep red color of the foliage. CO2 injection (15-25 mg/L) is highly recommended to promote robust growth and prevent leggy internodes, which would leave the lower stem bare.

Nutrition & Substrate: It prefers a rich and porous substrate, such as a fertile aquasoil, to support root growth. It requires constant liquid column fertilization rich in trace elements, chelated iron, and potassium. Deficiencies in these elements lead to fading of the upper leaves and necrosis of the older ones.

Water Chemistry: Highly temperature-tolerant (4°C to 30°C, with an optimal range between 22°C and 26°C). It adapts to acidic to neutral pH (5.0-7.0) and carbonate hardness between 0 and 14 dKH. Regular water changes promote healthy stems and prevent the accumulation of organic pollutants.

Space Management & Placement: Its height makes it ideal for the midground or background of the aquarium. It should be planted in small groups, spacing individual stems 2-3 cm apart so that light can penetrate to the lower leaves, preventing lower leaf loss caused by mutual shading.

Pruning: Pruning is done by cutting the upper part of the stem above a leaf node. The cut apical portion can be replanted directly into the substrate to propagate the plant, while the remaining bottom portion will quickly develop new lateral shoots, making the original clump bushier.

Risks & Diseases: It is sensitive to potassium deficiency (causing small holes in the leaves) and iron deficiency (resulting in pale or yellowish tips). If growth slows down due to lack of CO2 or light, the plant can easily be colonized by thread algae or green spot algae on the leaf margins.