[in Dutch with English summary: ] In the Netherlands species of Peltigera (dog lichens) are usually found in terrestrial and/or rupestrial habitats. Recently three Peltigeraspecies showed up as epiphytes on willow trees in tidal forests in Dutch freshwater tidal areas of the National Park the Biesbosch and of Klein Profijt near Rhoon. Peltigera didactyla was found in 2012 at two stations in the Biesbosch. The thalli established themselves on dead horizontal willow stems above water, above the daily high tide level. Apart from ubiquitous species like Brachythecium rutabulum, Kindbergia praelonga and Hypnum cupressiforme and the terrestrial Lunularia cruciata, the accompanying species were mostly hygrophytic, including Riccia fluitans, Drepanocladus aduncus and Lophocolea bidentata, indicating periodical flooding of the site. Peltigera neckeri was recorded for the first time in 2015 in Klein Profijt. Here, a very large thallus was found 1,4 m high on a slanting willow stem. In 2017 a fairly large population was also found in the Biesbosch in the ‘Ottergriend’. The Ottergriend is a low lying tidal forest, and is of bryological importance for the occurrence of the rare Timmia megapolitana. Peltigera neckeri was found here in mats of pleurocarpous mosses on willow stems well above the high tide water level. Surprisingly, this dog lichen was also found higher on younger parts of willow branches, up to 2.8 meters high, in company of, and overgrowing pioneer species like Orthotrichum affine, Cryphaea heteromalla, Metzgeria fruticulosa, Frullania dilatata and Parmotrema perlatum. Also in 2017 Peltigera praetextata appeared for the first time in the Ottergriend. Its thalli were found on three willow stems, growing well above the high tide water level. Two populations were observed in the vicinity of P. neckeri, overgrowing mats of common pleurocarps like Kindbergia praelonga and Hypnum cupressiforme. Unlike P. neckeri, thalli of P. praetextata were not observed on younger willow stems. Peltigera neckeri lacks means of vegetative propagation like soredia or isidia. Dispersion is dependent on spores formed by the mycobiont. Nonetheless a local population was established in the Ottergriend, a site devoid of cyanolichens up till now. We speculate that the theory of cyanolichen guilds could explain this phenomenon. After establishment, Peltigera praetextata may have acted as a ‘core’-species, spreading its symbiotic isidia onto trees in the vicinity. Under suboptimal conditions isidia will disintegrate and release their cyanobionts. Via its spores the mycobiont of a ‘fringe’-species like P. neckeri could have contacted the now free-living algae to form its own new symbiotic thallus. Of course, other explanations are possible, e.g. dispersal of P. neckeri by invertebrates or establishment of the mycobiont of P. neckeri on free living epiphytic Nostoc-algae.