The vertical distribution of Hymenophyllaceae species has been related to microenvironmental variations around host trees. We addressed the questions: Do the vertical microenvironmental conditions within forest stands of differing successional statuses vary significantly? Does the diversity of Hymenophyllaceae species differ between forest successional statuses? Are the vertical distribution and diversity of Hymenophyllaceae species related more to humidity or light availability? Are there any interspecific differences in the desiccation tolerance of these species which can be related to their vertical distribution? We characterized the microhabitat conditions (vapor pressure deficit [VPD], air relative humidity [RH], and light availability [PAR]) and the vertical distribution ofHymenophyllaceae species in host trees, in both a secondary forest and an old-growth temperate rainforest in Chile. Chlorophyll fluorescence was used to monitor the integrity of the photosynthetic apparatus during desiccation experiments. The stand basal area, tree height, and leaf area index were all significantly greater in the old-growth forest stands, but VPD, RH, and PAR showed no significant differences between the two forests. Both successional statuses showed the same amount of filmy fern species in terms of both abundance and diversity. In both successional statuses VPD and RH decreased while PAR increased with the height of the hosts. Regardless of the forest's age, abundance and diversity of filmy ferns were greater in microsites of greater humidity and less light availability. Desiccation tolerance differed significantly among Hymenophyllaceae species. The distribution pattern could be better explained by the specific microenvironmental requirements and desiccation tolerance rather than the forest's successional status.

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En este trabajo se estudia la germinación, el patrón de desarrollo morfológico y expresión sexual de dos especies de helechos homospóreos que habitan en Chile: Pteris semiadnata y Blechnum arcuatum. Para ello se recolectaron esporas de diferentes esporófi tos y se sembraron en cultivos de agar mineral, mantenidos en condiciones controladas. Los máximos porcentajes de germinación observados fueron 82 y 91% para B. arcuatum y P. semiadnata, respectivamente. El patrón de germinación en ambas especies se corresponde con el tipo Vittaria. El patrón de desarrollo morfológico de B. arcuatum se ajusta al tipo Aspidium. Los gametófi tos adultos de esta especie presentaron tricomas unicelulares por la superfi cie de la lámina y el margen, y se comportaron como unisexuales femeninos. Pteris semiadnata mostró un desarrollo de tipo Ceratopteris, originando gametófi tos adultos glabros. En este caso, hubo tanto gametófi tos bisexuales como masculinos, con un importante dimorfi smo sexual en cuanto a su tamaño. La aparición previa de protalos femeninos y el fuerte dimorfi smo sexual fueron indicios claros de la presencia de anteridiógeno. En ambas especies se generaron proliferaciones laminares vegetativas sobre los protalos.