Despite these promising applications, ferns, with their critical phylogenetic position as sister to seed plants, have largely been neglected in choosing the standardized barcode for all land plants. The DNA barcoding approach has also been useful in distinguishing among fern species in the horticultural trade and in Chinese herbal medicine, , two areas where species names are frequently confused. Recently, unknown fern gametophytes were shown to be identifiable, often to species level, by using plastid DNA sequences, ,, suggesting that this DNA-based identification tool has the potential to be applied to large-scale ecological surveys. ĭNA barcoding offers a possible solution to this problem and could greatly improve our understanding of fern gametophytes and their biology. As a result, ecological studies of gametophytes have largely been restricted to temperate regions where relatively few species exist, or to well-studied biological field stations in the tropics. However, because the morphology of fern gametophytes is so reduced, it has been very difficult to confidently assign gametophytes to species, or, frequently, even to particular genera. Although diminutive and inconspicuous, fern gametophytes are key players in fern ecology and biogeography: many are thought to have wider geographic distributions than their sporophytic counterparts –, some can exist indefinitely without producing sporophytes, , and others may be involved in hybridization events far outside the range of the parental sporophyte. Ferns and lycophytes are unique among land plants in that both sporophyte and gametophyte are not only visible to the unaided eye, but they are completely independent from one another. In all land plants-from bryophytes to angiosperms-the typical sexual life cycle involves the alternation of a diploid sporophyte phase with a haploid gametophyte phase.
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