A key for the identification of cryptospores

Dispersed spores interpreted as deriving from the earliest land plants have complex configurations (e.g. permanent dyads and permanent tetrads) and are readily distinguished from the more familiar trilete spores that often dominate post-Late Silurian dispersed spore assemblages. These forms occur mainly from the Middle Ordovician to Early Devonian. They were first recognised in 1971, but it was not until 1979 that the process of formal description commenced. In 1984 they were included in a newly created higher taxonomic grouping called ‘cryptospores’, the term reflecting their complex morphology and then the ongoing debate regarding their affinities. Subsequently the exact definition of the term cryptospore has been debated, with some preferring a wide definition encompassing all non-marine palynomorphs produced by algae and early land plants, but others confining inclusion to spores deriving from early embryophytes. Since their recognition, numerous ‘cryptospore’ taxa have been described. However, their complex morphologies are difficult to interpret and numerous taxonomic debates have confused the delineation of genera and their classification into higher ranks. Here we present a key for the identification of ‘cryptospore’ taxa with the aim of clarifying some of this confusion.