The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest eviden ce for land plants. They are first reported from the Llanvirn (Mid-Ordovici an). More or less identical assemblages occur from the Llanvirn (Mid-Ordovi cian) to the late Llandovery (Early Silurian), suggesting a period of relat ive stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryo phyte-like if not in fact bryophytes. In the late Llandovery (late Early Si lurian) there was a major change in the nature of dispersed spore assemblag es as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probabl y represents the appearance of vascular plants or their immediate progenito rs. A little later in time, in the Wenlock (early Late Silurian), the earli est unequivocal land plant megafossils occur. They are represented by rhyni ophytoids. It is only from the Late Silurian onwards that the microfossil/m egafossil record can be integrated and utilized in interpretation of the fl ora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New d iscoveries, novel techniques and fresh lines of inquiry are outlined and di scussed.