We studied south-Iberian populations of Trichomanes speciosum Willd. (= Vandenboschia speciosa (Willd.) Kunkel) (Hymenophyllaceae), an endangered filmy fern which appears in Annex II of the Directive 92/43 EC, as a species for which special conservation zones (ZEC) should be designated. In the southern Iberian Peninsula it is restricted to “Los Alcornocales” Natural Park (Cádiz and Málaga provinces, Andalusia region). It grows in nine populations (24 sub-populations), some of which contain very few individuals (2-4 sporophytes). Its habitat corresponds to the most humid and shaded parts of relict lauroid forests (Rhododendron ponticum). We describe as new the bryopteridophytic community of which it forms part (Homalio lusitanicae-Trichomanietum speciosi ass. nova), that colonises hollows and cavities of rocks exposed to water splashes and drips in the ravines within the lauroid forest. The phytogeographical importance of the bryophytic synusia that accompanies Trichomanes is pointed out. We propose a specific area within the Natural Park that should be set aside for conservation of this bryopteridophytic community, probably the best in continental Europe for sporophytes of Trichomanes.