, Volume 281, Issue 1-4, pp 77-86
Date: 17 Jun 2009

Identifying a mysterious aquatic fern gametophyte

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Süßwassertang, a popular aquatic plant that is sold worldwide in aquarium markets, has been long considered a liverwort because of its ribbon-like thallus. However, its antheridia are remarkably fern-like in morphology. To corroborate the hypothesis that Süßwassertang is a fern gametophyte and to determine its closest relative, we have sequenced five chloroplast regions (rbcL, accD, rps4trnS, trnL intron, and trnL-F intergenic spacer), applying a DNA-based identification approach. The BLAST results on all regions revealed that Süßwassertang is a polypod fern (order: Polypodiales) with strong affinities to the Lomariopsidaceae. Our phylogenetic analyses further showed that Süßwassertang is nested within the hemi-epiphytic fern genus Lomariopsis (Lomariopsidaceae) and aligned very close to L. lineata. Our study brings new insights on the unexpected biology of Lomariopsis gametophytes—the capacity of retaining a prolonged gametophytic stage under water. It is of great interest to discover that a fern usually known to grow on trees also has gametophytes that thrive in water.