Why does only a few studies on fern phenology exist? Perhaps this is the consequence of 3 prejudices: 1. Slow growth, 2. No growth or fertility rhythms as it is believed that ferns grow only under continually favorable humid conditions, and 3. Independence of pollinators for fertilization and animal vectors for their dispersal. Results of these study clearly prove that all 3 prejudices are not true for the mangrove fern Acrostichum danaeifolium. A population of 30 individuals was observed along a transect during one year in La Mancha (19°36’00’’N, 96°22’40’’W), Veracruz, Mexico. The climate is hot and humid with a dry season from November to March. Mean annual temperatures fluctuate between 22-26°C and annual precipitation varies between 1200-1500 mm. The study site is some 300 m from a brackish water lagoon, in the understory of the mangroves, dominated by Avicennia germinans (Avicenniaceae), where Acrostichum danaeifolium forms populations of 28.000 individuals per hectare. Phenological measurements were done biweekly. Individual daily leaf growth can reach up to 6-8 cm during the rainy season and slows down to 4 cm during the dry season, while the number of new buds and leaves shows little variation. Plants have a mean number of 8-10 sterile leaves, develop 1-2 leaves per month and the age of sterile leaves is around 9 to 12 months. The population was composed of 35 % of mature plants, which produce 1-3 fertile leaves only during the rainy season. Fertile leaves are alive for 2-3 months, so that there are no fertile plants during the dry season. Living gametophytes were present during the whole year, but especially abundant during the end of the dry season.

Key words: Acrostichum danaeifolium, ferns, mangrove, Mexico, phenology, Pteridaceae