Subclass Alismatidae ( Alismatidae )
Order Alismatales ( Alismatales )
Family Hydrocharitaceae ( Hydrocharitaceae )
Hydrocharitaceae are perennial, less often annual plants, partially or completely submerged in water. In appearance, they are so diverse that it is hard to believe they belong to the same family. Many Hydrocharitaceae are used or can be used as aquarium plants.
The subfamily Hydrocharitaceae is divided into 4 tribes: Ottelieae, Hydrochariteae, Stratioteae, and Enhaleae. The tribe Ottelieae includes the largest genus of the family, Ottelia. The tribe Hydrochariteae, besides the widely distributed Hydrocharis, also includes Limnobium and Hydromystria. All representatives of this tribe are rosette-forming plants floating on the water surface.
The only species of the tribe Stratioteae, Stratiotes aloides, is quite widely distributed in Eurasia. Growing rapidly, its rosettes often completely cover the surface of water bodies, creating a deceptive impression of green “lawns” through which it is not only impossible to walk, but also difficult to row a boat. The tribe Enhaleae also consists of a single species, Enhalus acoroides, distributed in the tropical part of the Indian Ocean.
The subfamily Vallisnerioideae is represented by 3 tribes: Hydrilleae, Vallisnerieae, and Blyxeae. The tribe Hydrilleae includes small-leaved Hydrocharitaceae with long branched stems. The largest genus, Elodea, includes 18 American species. Representatives of the genus Egeria, very similar in appearance to Elodea, have entomophilous flowers, however.
A well-known aquarium plant is Vallisneria spiralis. Besides Vallisneria, the tribe Vallisnerieae also includes the Western Australian genus Maidenia. The tribe Blyxeae comprises only a single, but very polymorphic genus Blyxa with 10 species. Within it, there are species with spaced and rosette-arranged leaves, with bisexual and unisexual flowers.
Genus Hydrilla — Hydrilla.
Hydrilla verticillata — Hydrilla verticillata.
(Eng. Pennywort). Hydrilla verticillata is easily confused with similar species of the genera Egeria, Elodea, and Lagarosiphon. Differences lie in leaf arrangement, number of leaves in a whorl, internode length, and leaf margin shape. Height 40 cm. A diverse aquatic plant 1-2 mm thick, with a soft stem more than 2 m long. Internodes are usually 0.5-2 cm long.
Leaves are sessile, stipules opposite, upper leaves in 3-6-parted whorls. Leaf blade linear to narrow-lanceolate, usually 1-2 cm long, transparent, soft, light to dark green, sometimes with a red central vein. Whorls of leaves and a rather powerful root system distinguish Hydrilla from Elodea canadensis. It is rarely kept in aquariums because it lacks high decorative value. The species is perfectly suited to aquarium maintenance conditions, so it can be kept in soft as well as hard, slightly acidic, or alkaline water.
It develops a strong root system and produces a large number of shoots. If plants are planted in the substrate, they soon have to be trimmed due to exceptionally rapid growth. At temperatures above 25°C, it grows worse; the higher the temperature, the longer the internodes. Planted in groups or left to float in the water column. Quickly forms thickets. If the tip is pinched, the plant develops lateral branches.
Propagated by separating young plants from the rhizome and by cuttings. Grows up to 5 cm per week. It forms thickets in Lake Tanganyika and is therefore suitable for setting up aquariums for fish from this lake, as well as Lake Malawi and Lake Victoria. Due to the fact that Hydrilla verticillata forms a grassy carpet, it is especially recommended for small spawning aquariums where plants are simply placed on the water surface. pH 6.5-7.5; dH 3-18°; T 20-25°C.
Hydrocharis morsus-ranae, Limnobium laevigatum, spongia.
Myriophyllum mezianum, Myriophyllum elatinoides, Myriophyllum pinnatum. 
