Spore morphology and wall ultrastructure of Hymenophyllaceae Link (Pteridophyta) from north-west Argentina

The family Hymenophyllaceae is represented in the study area by six species in two genera, Hymenophyllum J. E. Smith and Trichomanes L. The study was based on herbarium material and spores were studied under light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Both genera have trilete spores, 23 to 45 μm in equatorial diameter, with an ornamentation of echinulae and cones in Hymenophyllum and of verrucae, gemmae and granules in Trichomanes. Mature spores have a sporoderm composed of a perispore, an exospore and a fibrillar endospore; the exospore is 0.5 to 2.5 μm thick, compact and with an irregular margin. In some cases radial channels and other channels associated with the middle and inner parts of the laesurae were evident. A series of cavities filled with an opaque content line the inner margin of the exospore. The perispore is 20 to 400 nm thick and unevenly differentiated along the surface of a same spore. Under TEM, two main differentially contrasted portions could be distinguished: a dark massive portion with structural components could not be distinguished, and a light portion with several plates arranged in piles. The inner surface of the perispore exhibit short scales. Globules are immersed within the perispore at some depth from the perispore surface and others connected to it by structural threads. The spore characters observed including shape, ornamentation, laesurae length and wall structure are useful in distinguishing the two genera studied, but less useful in differentiation at the species level.