Among these, Radula visianica is assessed as Critically Endangered, with fewer than 50 individuals remaining in Austria, while others are threatened by climate change, habitat modification, and increased fire frequency.

Recent molecular phylogenetics analysis has refined understanding of relationships within the group, with the genus Porella identified as its closest relative.

The family Radulaceae was first described based on the genus Radula, established by the Belgian botanist Barthélemy Charles Joseph Dumortier in 1822.

[5] Spruce later elevated the group to Radulineae,[6] defined by keeled leaves with two unequal lobes, completely lacking underleaves, with perianths dorsiventrally flattened and truncate at the mouth, positioned at the end of the main shoot.

[7] Herbert Castle's 1936 worldwide monograph of Radula took a broader view of Cladoradula, expanding it to include all species with reproductive structures on short branches, regardless of other features.

However, later botanists, including Eustace W. Jones (1977),[8] Kohsaku Yamada (1979),[9] and Rudolf Mathias Schuster (1980),[10] returned to a narrower definition more aligned with Spruce's original concept.

The study revealed that subgenera Cladoradula and Dactyloradula were the earliest diverging lineages, representing the oldest evolutionary splits within the genus.

[7] Matthew Renner, Robbert Gradstein, and colleagues split the family Radulaceae into three genera in 2022, based on molecular and morphological evidence.

[7] The two groups that were elevated to genus rank, Cladoradula and Dactyloradula, were found to have diverged from the main Radula lineage during the Jurassic or early Cretaceous periods.

Additionally, both new genera possess a unique stem structure with an extra layer of cells called a subepidermis, which is absent in Radula.

This elevation is supported by comprehensive phylogenomic analyses using 228 nuclear genes, which showed that the Radulales diverged from related groups during the Permian period.

Molecular studies indicate Porella as its closest relative, sharing features such as bilobed leaves, perianth structure, and spore characteristics.

A characteristic feature of the family is its relatively flat (dorso-ventrally compressed) perianths, which are protective structures surrounding the reproductive organs.

The stems lack a subepidermis (additional cell layer beneath the epidermis) and typically develop innovations, or new shoots, from reproductive branches.

What makes this genus truly distinctive is the presence of finger-like appendages at the base of each leaf lobe, a feature not found in any other members of the family.

[12] Cladoradula species typically grow on the bark of trees and shrubs, as well as on shaded rocks in submontane and lower montane forests, where they often adopt a pendant growth habit.

Among the species evaluated by the IUCN, Radula visianica, endemic to Europe, is assessed as Critically Endangered, with fewer than 50 individual-equivalents (patches or colonies that function as single reproductive units) remaining in five localities in Austria.

[18] Radula jonesii, endemic to Macaronesia, is assessed as Endangered due to having fewer than 2,500 individual-equivalents across its range in the Canary Islands and Madeira.

[20][21][22] In contrast, Radula aguirrei, which is endemic to Colombia and known only from Gorgona Island in Cauca at 250 metres above sea level, is assessed as Least Concern due to its occurrence in a well-preserved protected area.

Habitat modification through forestry plantations and overgrazing poses challenges, as does water abstraction for hydroelectric schemes, particularly affecting populations in Ireland and Scotland.

Additional pressures come from increased fire frequency, the spread of invasive alien plant species, and various anthropogenic activities, including poorly managed ecotourism.