Gametophyte Features in a Peculiar Annual Fern,Anogramma leptophylla

Anogramma leptophylla is one of few homosporous ferns with ephemeral sporophytes and perennial gametophytic tubercules. This rare aspect of the life cycle has considerable bearing on the reproductive features of the gametophyte. Four populations in the Iberian Peninsula were selected to provide spores for laboratory cultures and to sample natural populations of gametophytes for comparative studies. Sexual expression and the role of the tubercule in the reproductive biology of this fern were studied. No significant differences were found between percentages of sexual versus asexual prothalli in natural populations or laboratory cultures, or between percentages of unisexual and bisexual prothalli. These results may indicate that sex in A. leptophylla is genetically determined instead of environmentally controlled as in most ferns. The presence of a gametophytic tubercule with nutrient reserves seems to be most favourable for the development of archegonia, and for the establishment of young sporophytes. This tubercule, which can resist stressful environmental conditions, allows for the development of new gametophytic outgrowths and of dormant embryos as soon as environmental conditions improve. This bryophyte-like behaviour gives this fern some advantages in colonisation and has probably contributed to its wide geographic range.