Spore mass and morphometry of some fern species

The knowledge of spore mass and size is fundamental to our understanding of dispersal of airborne spores and the biogeography of fern species. Thus, in the present study we present a simple method to measure mass of biological particles; the spore mass of 23 fern species was measured and related with spore size and type. Species could be grouped according to spore mass into three size classes 4-19 ng (twelve species), 37-46 ng (six species), and 69-90 ng (five species), which were not necessarily correlated to their level of ploidy. The highly variable spore mass of some species such as Blechnum falciforme might indicate the production of spores of different ploidy level. The average spore mass of all 23 species of 33.9 ± 6.03 ng is comparable to the mass of pollen grains, but three times lower than those reported for airborne orchid seeds. The average length of polar and equatorial axes of fern spores was 37.4 μm and 48.0 μm. The mean water content of fern spores was 1.7% and independent of storage time. The correlation between spore mass and the length of spore axes did not differ between monolete and trilete spores. Although fern spores do not differ from pollen grains in average mass, they might be less dense because of their high lipid and low water content, both promoting increasing airlift.