Two River Mosses New to Liguria Reveal Hidden Links Between Water Quality and Geology

In the streams and rivers of Liguria, a narrow arc of northwestern Italian coastline wedged between the Alps and the Mediterranean Sea, two aquatic moss species have quietly gone unnoticed by regional botanists until now. During routine macrophyte surveys carried out between 2014 and 2023 on behalf of the Regional Environmental Protection Agency ARPAL, researchers documented Cinclidotus riparius and Cinclidotus danubicus, two members of the moss family Pottiaceae, for the first time in the region. The discovery, published in the Italian Botanist, is more than a simple addition to a regional checklist: it offers a vivid illustration of how geology, hydrology and living organisms intertwine in river ecosystems, and how even the smallest plants can serve as sentinels of environmental health.

The surveys were not a random botanical expedition. They formed part of the monitoring obligations arising from the European Water Framework Directive, transposed into Italian law through Legislative Decree 152/2006, which requires member states to assess the ecological status of water bodies using biological quality elements. Among these elements are aquatic macrophytes, a broad assemblage that includes algae, bryophytes, ferns and flowering plants. Bryophytes, the group containing mosses and liverworts, are particularly important because they occur in virtually all watercourses and often dominate the mountain stretches where rocky substrates prevail. Certain genera, and Cinclidotus is a prime example, are so tightly bound to specific water chemistry and substrate conditions that their presence or absence can signal whether a river is in good or poor ecological condition.

The fieldwork followed the national ISPRA protocol, with surveyors crossing and examining each river reach from bank to bank, taking into account the characteristic flow facies and the vegetation present. Two campaigns were run each year, one in spring and one in late summer or autumn, timed to coincide with the period of maximum vegetative development of the aquatic community. This rigorous, repeated sampling design meant that when the two Cinclidotus species appeared, they did so within a framework of standardized ecological assessment, giving the records both botanical and water-management significance. Specimens were identified using established taxonomic keys and deposited in the Cryptogamic Herbarium of the University of Camerino.

The genus Cinclidotus comprises twelve species distributed mainly across the Northern Hemisphere, with its greatest diversity in northwestern Europe, where countries such as France, Switzerland, Austria and Germany each record six species. In Italy, only four species are known: C. riparius, C. aquaticus, C. fontinaloides and C. danubicus. The first three are widespread across many Italian regions, but C. danubicus had previously been reported from just two areas, Friuli Venezia Giulia in the northeast and Lazio in central Italy. These mosses are structurally robust plants, mostly forming upright tufts anchored to their substrate by a basal disc, dark green to almost black in color, with isodiametric leaf cells and margins several cell layers thick. They favor coarse, stable substrates such as boulders and rocks in fast-flowing water, and some species tolerate periodic drying while others require permanent submersion.

Cinclidotus danubicus is the rarer and more remarkable of the two Ligurian newcomers. A medium-sized moss reaching up to 15 centimeters in height, it forms loose or dense tufts, irregularly branched with long lateral branches, and is green-brownish in color. Its rigid leaves are contorted or slightly incurved when dry and elliptic-linear to narrowly lanceolate when moist, up to 3 to 4 millimeters long, with a unistratose lamina, thick basal costa and bistratose, plane margins. The species has a geographically restricted range confined to a handful of northwestern European countries. In Italy, prior to the Ligurian find, only two records existed: a recent one along the Risorgiva del Timavo in Friuli Venezia Giulia and an older one from the banks of the Tiber near Ponte Palatino in Rome, where targeted searches in recent years have failed to relocate it because of major environmental changes along the river.

The Ligurian specimen of C. danubicus was collected on June 3, 2020, in a stretch of the Aveto River upstream of Ponte Principe sull’Aveto toward Alpepiana, between the municipalities of Rezzoaglio and Santo Stefano, at 654 meters above sea level. The site lies within the Natura 2000 area IT1331104, the Parco della Val d’Aveto, designated as a Special Area of Conservation under the Habitats Directive. It is a virtually undisturbed location with only minimal upstream nutrient input, qualities that identify it as a reference site for classifying the ecological status of the water body. Geologically, the stretch sits within formations of calcareous-marly flysch, the Flysch of Ottone and the Flysch of Monte Rocco, and the moss was found on large boulders and calcareous rocks washed by flowing to fast-flowing water in the more marginal portions of the active channel, areas subject to periodic submersion.

The biological company at the Aveto site reinforces its ecological value. Alongside C. danubicus, the surveyors recorded other bryophytes including C. fontinaloides, Cratoneuron filicinum and Rhynchostegium riparioides, while the community as a whole was dominated by algal taxa such as Cladophora, Diatoma and Spirogyra. The riparian belt consisted of a typical formation dominated by Salix eleagnos, Salix purpurea, Alnus glutinosa and Alnus incana, with hazel, ash and dogwood in supporting roles, and the surrounding woodlands were composed mainly of downy oak and black alder forests. This assemblage paints a picture of a functioning, near-natural river corridor, exactly the kind of environment that a rare, sensitive moss would be expected to occupy.

Cinclidotus riparius tells a very different story of distribution. This species forms compact or loose tufts up to 8 centimeters tall, dark green to blackish, with erect leaves that are ovate-elliptic to narrowly ligulate and margins that are strikingly thick, composed in cross-section of two to five layers of cells of similar size. It is widespread across Europe and has been recorded in recent years in numerous Italian regions, from Valle d’Aosta and Piemonte in the northwest to Sicily in the south. In Liguria, it was repeatedly found at 39 monitoring sites across various watercourses throughout the entire monitoring period, mainly along the marginal portions of the active riverbed and, more sporadically, in submerged sections influenced by natural or artificial fluctuations in discharge. It frequently grew alongside other bryophytes such as C. aquaticus, C. fontinaloides, Rhynchostegium riparioides, Palustriella commutata and Cratoneuron filicinum.

Perhaps the most striking analytical result of the study emerged when the researchers overlaid the occurrence sites of C. riparius onto regional geological mapping. The records clustered strongly within the two lateral quadrants of the Ligurian territory, inland and along the hilly areas of the eastern sector from roughly Cornigliano Ligure to the Tuscan border, and in the western sector from Borghetto Santo Spirito to the French border. Both quadrants share a typically calcareous-marly lithology, and the single C. danubicus locality also falls within the western quadrant. In contrast, the central area between the two quadrants, dominated by acidic volcanic formations including gneiss, serpentinites and ophiolites, yielded no significant findings. The correlation between moss distribution and underlying geology is strong, pointing to a clear preference for calcareous substrates. Beyond lithology, all sites shared common hydromorphological traits: torrent-like segments, shaded conditions, stable coarse substrates of boulders and rocks, moderately to highly turbulent waters, and marginal areas of moderate to slow flow shaped by fluvial dynamics.

For the researchers, the two species carry considerable weight as bioindicators of the ecological integrity of watercourses and their ecosystems. The single, isolated record of C. danubicus underscores both its rarity within Italian territory and the importance of protecting the pristine Aveto stretch where it survives. Meanwhile, the broad, geologically patterned distribution of C. riparius demonstrates how routine monitoring designed for water management can simultaneously generate fundamental biogeographical knowledge. The authors suggest that integrating additional sampling sites and new watercourses within the Ligurian hydrographic network may, in the future, allow further insights into the ecology and distribution of these two mosses, potentially revealing whether the Aveto population of C. danubicus is a relict, a recent arrival, or simply the first visible trace of a species that has long been overlooked in the region’s rivers.

Subject of Research: First records of the aquatic mosses Cinclidotus danubicus and Cinclidotus riparius in Liguria and their correlation with river geology and ecological quality

Article Title: Cinclidotus danubicus and C. riparius ( Pottiales , Pottiaceae ), two interesting moss species of watercourse ecosystems new to Liguria

Article References: Spada, C. D., Olivieri, L., Aleffi, M., & Aleffi, A. (2026). Cinclidotus danubicus and C. riparius (Pottiales, Pottiaceae), two interesting moss species of watercourse ecosystems new to Liguria. Italian Botanist, 21, 47-57. https://doi.org/10.3897/italianbotanist.21.182900

Image Credits: AI Generated

DOI: 10.3897/italianbotanist.21.182900

Keywords: Cinclidotus danubicus, Cinclidotus riparius, bryophytes, mosses, Liguria, watercourses, bioindicators, macrophytes, Water Framework Directive, river ecology, calcareous substrates, Natura 2000