Introduction

Although studied less than aquatic diatoms, aerial diatoms are discussed in an extensive literature. Most publications on the topic consist merely of floristic lists. Thus our understanding of aerial diatom ecology is meager. Given the brevity of the current chapter, it is not possible to list all of the pertinent literature. This paper will summarize aerial diatom studies based on floristic literature and my own work.

The most important early worker was probably Johannes Boye Petersen. Unlike many early soil phycologists, he treated diatoms with both detail and taxonomic accuracy. Petersen (1915, 1928, 1935) examined numerous aerial samples from Denmark, Iceland, and East Greenland. In all, he described 196 diatom taxa from soils, wet rocks, wet tree bark, and mosses, many of which were new to science at that time.

Other important early floristic works are those of Beger (1927, 1928), Krasske (1932, 1936, 1948), Hustedt (1942, 1949), Lund (1945), and Bock (1963). More recent studies report diatom floras associated with limestone caves, sandstone cliff faces, wet rocks, mosses, and soils. Added to these studies are numerous papers on aerial algae which discuss diatoms to some extent. Reviews on terrestrial algae have generally slighted the diatoms, although none have ignored them (Johansen, 1993; Metting, 1981; Novichkova-Ivanova, 1980; Starks et al., 1981; Hoffman, 1989).

Petersen (1935) defined a number of categories for aerial algae based on their habitat type. Euaerial algae inhabit raised prominent objects that receive moisture solely from the atmosphere.