In principle, aquatic and marsh plants can reproduce in two ways: sexually and asexually. During sexual reproduction they form seeds (in the higher flowering plants) or spores (mosses and ferns). These emerged from the fertilization of the flowers and contain the genes of both parents, i.e. the male and female plants or the male and female flowers of one and the same plant. The seeds germinate and grow into new plants.
Why should you propagate the Aquarium?
Since our aquarium plants often only bloom as emersed marsh or land plants in their exotic home and often do not bloom at all in our aquariums as predominantly submerged, submerged plants, sexual, generative reproduction only plays a subordinate role in most aquarium plants. Instead, they reproduce asexually, i.e. vegetative, in that they divide, form cuttings and daughter plants or underground runners which at some point detach from their mother plant. This plant always has the same genes as the mother plant. Since only one partner is involved in the reproduction.
All vegetatively propagated plants are therefore a genetic clone of their mother plants. As a result, some aquatic plants, such as the Canadian waterweed, which originally came from North America, are only ever found in female specimens in our Central European waters. Presumably, all native populations of this waterweed come from a single female specimen that was once introduced here from North America.
Whenever new cultivars of aquarium plants are offered e.g. Red-leaved instead of green-leaved or small-growing plants that do not occur naturally in this way, then these must have been created by crossing at least 2 parent plants, i.e. by sexual reproduction. A spontaneous mutation in a mother plant, on the other hand, is extremely rare and unlikely.
But there are some aquatic plants that can also be sexually reproduced by hobby aquarists. They either bloom spontaneously or you have to help a little. Many floating-leaf plants form floating leaves and flowers that protrude beyond the surface. In nature they are pollinated by wind and insects; under aquarium conditions, artificial insemination can be done with a brush. The fertilized seeds then either sink underwater to the bottom of the aquarium. However, many only germinate on a moist, but not overflowing, surface. Such conditions can be created, for example, in a paludarium with a water and a land part.
In most aquarium plants, including the water goblet Cryptocoryne, sword plants Echinodorus, swamp friends Hygrophila, the Ludwigia species and many other common aquarium plants, only vegetative reproduction is possible under aquarium conditions. No more than 5 to 6 species are currently used in the nurseries specializing in the cultivation of aquatic plants for commercial propagation from seeds – e.g. Echinodorus berteroi and Samolus parviflorus.
In contrast, vegetative propagation is quite uncomplicated for most aquarium plants and should definitely be used by hobby aquarists.
How to propagate Stem plants
Like many garden plants, stem plants can easily be propagated vegetatively with the help of cuttings. Head cuttings are cut from the top of the stem plant. Since they contain the vegetation cone in the tip of the shoot, such cuttings grow into new plants the fastest.
The lower leaves are removed and the head cuttings are placed in the ground at a distance from the mother plant. New roots will form there quickly. Every part of the stem plant can be used for vegetative propagation.
The side shoots of the mother plant can also be used for this. Or shoot cuttings that are cut from the middle part of the plant after the tip of the shoot has already been cut off as a head cutting. A prerequisite for a new plant to develop from such shoot cuttings is, in addition to the formation of roots, that one of the leaf axils develops a side shoot. But also from the base, which is still left from the mother plant after this procedure, side shoots soon sprout again from the buds and leaf axils. In this way, the stem plant becomes a richly branched bush.
The same effect can also be achieved by regular pruning, even if either part of the stem is not used for propagation.
How to propagate: Roots
Roots are formed by many aquarium plants that grow out of the leaf axils, especially from the side shoots, and more rarely from the tip of the shoot.
These roots spread partly just above the ground, partly underground. They come to the surface from section to section and new plants emerge from the buds of these roots.
Species that reproduce in this way soon conquer the entire terrain with their roots. As soon as the young plants have reached a few centimeters in height, they can be separated from the mother plant and removed from the aquarium or planted elsewhere.
Otherwise the connection to the mother plant will cut itself off after a while. Some floating plants also spread through such roots.
How to propagate: Offshoots
Offshoots arise in a similar way, but are formed on shorter branches of the mother plant.
An even closer connection between mother and daughter plants is entered into in the development of adventitious plants. Such adventitious plants usually form on the leaf edges of the mother plant.
If they are big enough and strengthened, the adventitious plants separate from the mother plant and are driven away with the current.
How to propagate: Meristem multiplication
A relatively new method is the plant produced from cell culture, the so-called meristem propagation,
as it is mainly used by professional aquatic plant nurseries for the vegetative propagation of new varieties.
A pile of cells from the plant is grown in a sterilized nutrient solution and, with the addition of phytohormones, a small plant is grown under laboratory conditions.
Especially if only a single plant, for example a reddish color mutant, is available as the starting material, this is often the only way to produce as many genetically identical daughter plants as possible.