Comparative analysis of spores of Alsophila (Cyatheaceae) species from southern South America

Abstract

The spore morphology and wall ultrastructure of five species of Alsophila (Cyatheaceae) present in the southern South America were studied with light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The spores are trilete, 34.2 to 60.6 μm in equatorial diameter and 23.4 to 44.0 μm in polar diameter. The exospore is 1.1 to 3.3 μm thick and smooth. In section it is two-layered and depending on the sectioning plane channels are evident. The perispore is 0.6 to 5.8 μm thick, two-layered in section, and bears ridges that are cristate in some species. The perispore inner layer is composed of three-sublayers: the inner stratum is alveolar, the middle stratum is composed of muri traversed by thin channels, and the outer stratum is homogeneous. The perispore outer layer uniformly consists of threads and is perforated. These structural elements also constitute the ridge surface. Globules are occasionally present both on the surface or immersed within the perispore. A basic wall structure is recognized for Alsophila spores while differences were found at a specific level regarding sculpture. The spore wall organization and stratification of Alsophila was found to be similar to that found in Sphaeropteris within the Cyatheaceae, and this structure is apparently unique among ferns.