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Cryptospores have been recovered from rocks from the Ordovician through the Devonian period (485.4-358.9 million years ago), and knowledge of cryptospores is essential to our understanding of the earliest land flora. Cryptospores were produced by small, simple terrestrial organisms – cryptophytes – that possessed a combination of features not found together in current living species. While evidence about cryptophytes has been obtained from spores extracted from small fossil fragments, many aspects of overall cryptophyte morphology, biology and affinity remain unclear. Cryptophyte lineages The cryptophyte group of plants is very diverse, and cryptophytes are the common ancestors of both modern bryophytes and vascular plants. In modern land plants, spores are dispersed as single units (monads) whereas the cryptophyte spores were dispersed as dyads (two units) and tetrads (four units). Two distinctive groupings of cryptophytes are currently recognised: Partitatheca and Lenticulatheca. The Partitatheca group includes plants with stems that divide into two branches and end with sporangia that have stomatal pores. The spores are dyads with a laminated wall structure. Lenticulatheca have disc-shaped sporangia containing monads formed from dyads with a structure closer to that of higher plants. Dyads versus tetrads Cryptophyte sporogenesis always produced either dyads or tetrads, indicating strict genetic control. Finding dyads inside cryptophyte sporangia proves that this cryptospore type derives from land plants. This finding challenges the long-held consensus that pioneering land plants only produced tetrads (resulting in four spores, each with a single set of chromosomes). The possibility that dyads are the original state in land plants should be given serious consideration. The displacement of cryptophytes The demise of the cryptophytes is poorly understood in causal terms, but spores derived from larger vascular plants, mostly zosterophylls, diversified and this was accompanied by a major decline in cryptospores, suggesting that cryptophytes were displaced by local competition with zosterophylls. This diversification and rapid increase in size of the vascular plants during the Early Devonian period is thought to have resulted in the evolution of the first forest ecosystems.

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This page is a summary of: Cryptospores and cryptophytes reveal hidden diversity in early land floras, New Phytologist, January 2014, Wiley,
DOI: 10.1111/nph.12645.
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