Ferns are famous among experts for their huge genome: the record is held by a species with 720 pairs of chromosomes, each cell nucleus contains 148 billion base pairs, humans only have a fraction of this with around 3 billion base pairs.

Although they are the second largest group of vascular plants after seed plants, with more than 10,000 species, their genomes have tended to be neglected.

They can use tricks to defend themselves against being eaten by pests and are exceptionally drought-resistant – properties that should actually arouse the interest of scientists.

The fact that ferns have so far been a stepchild of research has to do not only with the sheer size of their genomes and the lack of a reference genome for navigating in the genome, but also with a lack of financial incentives: there is mainly money for crop research.

A few days ago, international research teams presented two new reference genomes in the journal "Nature Plants".

It is the genome of a maidenhair fern and the genome of the horn fern Ceratopteris richardii, also known as the C fern.

The C fern is familiar to many aquarium owners because it can live not only on land, but also under water.

Both genomes form the basis for long overdue research into the properties of ferns and provide initial answers to the question of where the genetic material hoarded by this plant group comes from.

Ferns take on a great burden because they have to duplicate the entire DNA before each cell division, which requires a lot of energy and materials.

So why all this effort?

A "colorful bouquet" of genetic sequences

The C fern genome is large, but not gigantic.

It has 7.46 billion base pairs, 39 pairs of chromosomes and 36,857 genes.

It is striking that the size of the genome cannot be explained by the repeated doubling of the genome, but rather by so-called jumping genes, which have repeatedly copied and integrated themselves into the genome.

This makes the genome of the C fern a potpourri of large and small DNA fragments, genetic debris and these jumping genes, which make up about 85 percent of the genome.

The team of authors, led by three biologists at Stanford University in California, speaks of a "motley bouquet" of genetic sequences.

It is also remarkable that the jumping genes have led to interruptions in the actual genes, thereby pulling them apart.

It is not uncommon for the gene pool of plants to expand through duplications and jumping genes.

This gives them access to new genetic material and gives them the opportunity to better adapt to their environment.

What is surprising, however, is that the C fern appears to make little effort to clean up its genome and shed genetic ballast - unlike most other vascular plants have done in the course of their evolution after they had increased their genetic makeup.

The C fern holds onto much of what has accumulated in its nucleus.

Why is that?