Genus Asplenium is one of the most various genus of ferns in flora of Croatia. The external appearance of the members of this genus can vary considerably. Furthermore, frequent mutual hybridization can lead to difficulties in identification due to the large morphological similarities and overlappings of characters. In the flora of Croatia there are 20 species of this genus, and two of them are considered to be endangered (EN), one of them is almost endangered (NT) and the another one is critically endangered (CR). Both species belong to the genus Phyllitis by old classification, and they are Asplenium hybridum and Asplenium sagittatum which inhabit the area of Kvarner. Most frequently, spleenworts can be found by the Adriatic coast and several species have their centers of distribution in continental part of Croatia. Mountain sites with limestone substrate, various rock and wall cracks and cave enters are the most typical habitat where we can find species of this genus. They are extremely adapted to the Mediterranean climate which is often quite harsh and possibly disastrous to the other ferns. Due to this very specific adjustment genus, Asplenium is considered to be one of the most thermophilic fern genera.