Enkele vondsten van Rhytidiadelphus triquetrus met kapsels

In the winter of 1995 fruiting populations of the moss Rhytidiadelphus triquetrus were discovered on seven localities in the sand dunes on the isle of Texel. The last find of capsules of this species in the Netherlands dated from 1942. Possible reasons for the rareness of the fruit of this moss are briefly discussed. Firstly, it is supposed that – given the lack of deliberate search for capsules – under-recording may give a false picture. Another explanation may be found in the possibility that the moss only fruits in one or a few specific habitats and will remain sterile in its other stations. This is also suggested by the Texel situation of 1995, in which all finds were made in exactly the same habitat. This is to be found on steep, north-facing slopes that are dominated by Empetrum nigrum, with admixtures of Calluna vulgaris and Rosa pimpinellifolia. Carefull searching in many other, far richer growing places of the moss revealed no fruit. This was all the more remarkable because only a small proportion of the total amount of Rhytidiadelphus triquetrus on the isle (probably less than 10%) is to be found in the habitat just described. Finally it is suggested that the extremely mild winters of the past few years may have played an important role in the formation of sporophytes. Only through more systematic recording of sporophytes, in combination with collection of data on climate and habitat, more light may be thrown on this matter.