Recent discovery of the small pillwort (Pilularia minuta Durieu, Marsileaceae) in Tunisia: hope for an endangered emblematic species of Mediterranean temporary pools?

This article presents a synthesis of all localities where Pilularia minuta, an endangered Pteridophyte endemic of acidic Mediterranean temporary pools, was observed since its discovery in 1835. It aims at analysing the implications of its recent discovery in Tunisia, based on the comparison between new and previously published floristic surveys. The obtained data confirm the heliophilous pioneer character of P. minuta and reveal a disturbance-favoured behaviour in Tunisia. The small pillwort, which occurs in 16 locations around the Mediterranean basin, could be characterised by a good dispersion. However, it experienced the extinction of a quarter of its known populations over the last century. This decline seems to have affected only small populations (Maritime-Alps, France; Lazio, Italy) and highly disturbed areas (Algeria), while large ones (Sardinia, Italy; Corsica and Hérault, France; Andalusia, Spain; western Morocco), presumably more stable, survived. In a context of metapopulation, these large populations could be considered as 'source populations', and should be taken more especially in account in conservation strategies. Further investigations are needed for improving the conservation of the rare plants of Mediterranean temporary pools as well as contributing to a better knowledge of the mechanisms controlling their distribution and their present-day status.