Megaspore germination and sporophyte emergence requirements in the critically endangered endemic quillwort Isoëtes malinverniana

Isoëtes malinverniana is a critically endangered quillwort endemic to north-western Italy. Although some aspects of its reproductive biology are well known, megaspore and sporophyte germination ecology have never been studied in detail. In this study, we investigate and clarify the thermal requirements for megaspore germination and sporophyte emergence in I. malinverniana . We tested the effect of five constant temperatures (10, 15, 20, 25, 30 °C) and one alternating temperature (25/15 °C) on megaspore germination and sporophyte emergence in I. malinverniana . Moreover, we tested the effect of light and dark on megaspore germination and, the species self-compatibility and apomictic reproduction. Our results suggest that the optimal temperatures for megaspore germination and sporophyte emergence were 20 °C and 25/15 °C, reaching approximately 80 % germination at these temperatures after eight weeks. Spore germination did not occur at 10 °C and decreased at temperatures above 25 °C. Germination and emergence speed were also positively related to temperature. Megaspore and sporophyte of I. malinverniana germinated and emerged in the dark, but at a lower percentage than in full light. Our study suggests that I. malinverniana is self-compatible and cannot reproduce apomictically.