Plant Syst Evol (2009) 281:77–86 DOI 10.1007/s00606-009-0188-2 ORIGINAL ARTICLE Identifying a mysterious aquatic fern gametophyte Fay-Wei Li Æ Benito C. Tan Æ Volker Buchbender Æ Robbin C. Moran Æ Germinal Rouhan Æ Chun-Neng Wang Æ Dietmar Quandt Received: 5 January 2009 / Accepted: 11 May 2009 / Published online: 17 June 2009 Ó Springer-Verlag 2009 Abstract 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 F.-W. Li (&)
C.-N. Wang (&) Department of Life Science, National Taiwan University, Taipei 106, Taiwan e-mail: fayweili@gmail.com C.-N. Wang e-mail: botwang@ntu.edu.tw sequenced five chloroplast regions (rbcL, accD, rps4–trnS, trnL intron, and trnL-F intergenic spacer), applying a DNAbased 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. B. C. Tan The Herbarium, Singapore Botanic Gardens, Singapore 295969, Singapore Keywords Aquarium
DNA barcoding
DNA-based identification
Gametophyte
Fern
Lomariopsis
Lomariopsidaceae V. Buchbender
D. Quandt (&) Plant Phylogenetics and Phylogenomics Group, Institute of Botany, Dresden University of Technology, 01062 Dresden, Germany e-mail: dietmar.quandt@tu-dresden.de; quandt@uni-bonn.de Introduction R. C. Moran The New York Botanical Garden, Bronx, New York, NY 10458-5126, USA G. Rouhan Muséum National d’Histoire Naturelle, UMR 7205, Herbier National, CP39, 16 rue Buffon, 75005 Paris, France C.-N. Wang Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei 106, Taiwan Present Address: D. Quandt Nees Institute for Biodiversity of Plants, University of Bonn, Meckneheimer Allee 170, 53115 Bonn, Germany An aquatic plant called Süßwassertang, which means ‘‘freshwater seaweed’’ in German, has been commercially available on the aquarium market worldwide for a number of years (Fig. 1a). Because of its liverwort-like appearance, it has long been considered to be a liverwort, such as Pellia or Monoselenium. Our observation of Süßwassertang gametangia, which are only rarely produced by the submerged thallus, suggested that this plant is not a liverwort but a fern gametophyte. Its archegonia are fern-like in having short necks, and the venter is immersed partly in the thallus. The antheridia resemble those of polypodialean ferns in that they consist of three cells: a cap cell, a ring cell, and a basal cell (Fig. 1b; Nayar and Kaur 1971). Although gametangia are present occasionally, sporophytes 123 78 F.-W. Li et al. Fig. 1 Süßwassertang, its microscopic features, and the habit of Lomariopsis spectabilis. a A portion of the gametophyte thallus showing extensive lateral branching. Bar: 1 cm. b Side view of an antheridium, showing a cap cell (cc), ring cell (rc), and basal cell (bc). Bar: 20 lm. c Scanning electron microscope image of developing lateral branches with rhizoids (arrowhead) and meristems (m) in the rounded apex. Bar: 0.2 mm. d Ribbonlike, branched gametophyte (g) of L. spectabilis bearing a young sporophyte (sp) in a field of Taiwan. It has similar morphology with the mysterious gametophyte. Arrowhead Branch points. Bar: 1 cm have never been observed in aquaria and even after planting onto soil. It is therefore difficult to identify the plant with certainty. To unravel this mysterious identity, we employed a DNA-based identification approach consisting of sequence comparisons and phylogenetic analyses. We sequenced five chloroplast regions [rbcL, accD, rps4–trnS, trnL intron, and the trnL-F intergenic spacer (IGS)], of which rbcL has already been successfully used to identify an unknown fern gametophyte in a similar study (Schneider and Schuettpelz 2006). The widespread occurrence of rbcL in online databases for all plant lineages makes it well-suited for broadscale screening. Likewise, the analyses by Quandt et al. (2004) indicated that the trnL-F region (intron and IGS) has the power to relate any sequence via a database comparison on generic level in most land plant lineages. The rapidly evolving gene rps4 (plus rps4–trnS IGS) was included because it represents one of the broadly sequenced regions (together with the trnL-F region and rbcL) in seedless plants (e.g., Quandt and Stech 2003; Schneider et al. 2004). In the approach chosen here, BLAST results pinpointed which clade Süßwassertang belongs to and therefore guided the taxonomic sampling for phylogenetic inferences. To increase the phylogenetic signal, we combined accD with rbcL in the analyses. Once narrowed to a certain lineage, a more precise marker was then used to resolve the position of Süßwassertang among more recently diverged lineages. In this case, the plastid trnL-F IGS was employed to infer inter-species affinities of this supposedly aquatic fern gametophyte. 123 Materials and methods Taxonomic sampling for molecular phylogeny Taxonomic sampling was guided by the MegaBLAST (Zhang et al. 2000) results obtained from the five regions sequenced (rbcL, accD, rps4–trnS, trnL intron, and trnL-F IGS). To obtain more robust confirmation of the relationship of Süßwassertang, we compiled two data sets for phylogenetic analyses. As indicated by the BLAST results, the first data set comprised a representative set of sequences from two coding plastid regions, rbcL and accD, of polypod ferns. In addition to the Süßwassertang sequences, 32 species representing 28 fern genera were included in the analyses. Athyrium niponicum (Mett.) Hance and Matteuccia struthiopteris (L.) Todaro were used as outgroups. The second matrix included all available trnL-F IGS accessions of Lomariopsis plus sequences obtained from two Süßwassertang accessions, L. spectabilis (Kunze) Mett., and Cyclopeltis crenata (Fée) C. Chr. Cyclopeltis crenata and Hypodematium crenatum Kuhn ex v. Deck. were used as outgroups for the second matrix. DNA extraction, amplification, and sequencing Total genomic DNA was extracted using either the Plant Genomic DNA Mini kit (Geneaid, Taipei, Taiwan) or the Plant Genomic DNA Purification kit (GeneMark, Taichung, Taiwan). In some cases a modified CTAB (cetyl trimethylammonium bromide) procedure (Wang et al. An aquatic fern gametophyte 2004) was applied. The PCR amplifications, which followed standard PCR protocols, were performed in 50-ll reaction volumes containing 1.5 U Taq DNA polymerase, 1.0 mM dNTPs-Mix, 109 buffer, 1.5 mM MgCl2, 10 pmol of each amplification primer, and 1.0 ll DNA. The PCR primers used for amplification and sequencing were: trnL-F with primers C (or E) and F (Taberlet et al. 1991; modifications according to Quandt and Stech 2004); rps4 (plus rps4–trnS IGS) with rps50 (Nadot et al. 1994) and trnS (Souza-Chies et al. 1997); rbcL with NM34 (Cox et al. 2000) and M1390 (Lewis et al. 1997); accD with the newly designed primers ‘‘FW_accDF’’ (50 -ACG TCT GTA ACA AAT TGG TTT GAA G-30 ) and ‘‘FW_accDR’’ (50 -AAA CTC AAC GTT CCT TCT TGC AT-30 ). The PCR products were either directly purified using the GeneMark PCR Clean-Up kit (Taichung, Taiwan) or cleaned via gel extraction employing the Nucleospin PCR Purification kit (Macherey-Nagel, Düren, Germany). Sequencing was done with the amplification primers by Macrogen (Seoul, Korea). In order to corroborate the results, isolation, amplification, and sequencing of all regions were performed independently on two different samples in Taipei and Dresden. Newly obtained sequences and other accessions from GenBank used in the analyses are summarized in the Appendix. Sequence alignment and phylogenetic analyses DNA sequences were manually aligned using PhyDE0.995 (Müller et al. 2005). During manual alignment, gap placement was guided by the identification of putative microstructural changes following recently published concepts (Kelchner 2000; Quandt et al. 2003). Identified inversions were positionally separated in the alignments, but they were included as a reverse complement in the phylogenetic analyses, as discussed in Quandt et al. (2003). Phylogenetic reconstructions using parsimony were performed using winPAUP* 4.0b10 (Swofford 2002) in combination with PRAP (Müller 2004). The latter program generates command files for PAUP* that allow parsimony ratchet searches as designed by Nixon (1999). In our study, ten random addition cycles of 200 ratchet iterations each were used, with 25% of the positions being randomly double-weighted. The shortest trees collected from the different tree islands were finally used to compute a strict consensus tree. Heuristic bootstrap searches (BS; Felsenstein 1985) were performed with 1000 replicates, ten random addition cycles per bootstrap replicate, and otherwise the same options in effect as in the ratchet. For a further measurement of support, posterior probabilities were calculated using MrBayes V3.1 (Ronquist and Huelsenbeck 2003), applying the GTR ? C ? I model. The a priori probabilities supplied were those specified in 79 the default settings of the program. Posterior probability (PP) distributions of trees were created using the Metropolis-coupled Markov chain Monte Carlo (MCMCMC) method and followed the search strategies suggested by Huelsenbeck et al. (2001, 2002). Ten runs with four chains (106 generations each) were run simultaneously. Chains were sampled every ten generations, and the respective trees were written to a tree file. Calculation of the consensus tree and of the PP of clades was performed based upon the trees sampled after the chains converged (within the first 250,000 generations). Consensus topologies and support values from the different methodological approaches were compiled and drawn using TreeGraph (Müller and Müller 2004). Results BLAST results of the sequenced markers The sequences (rbcL, accD, rps4-trnS, trnL intron, and trnL-F) obtained from two independent collections of Süßwassertang were identical. BLAST results indicated that Süßwassertang shares high sequence similarities to leptosporangiate ferns and is closest to the Lomariopsidaceae (except for trnL intron), especially in terms of the reported maximum identity (Table 1). Lomariopsis lineata (C. Presl) Holttum was found to be the best match for the trnL-F IGS, whereas for the three coding regions (rbcL, accD, and rps4), L. spectabilis Mett. or L. marginata (Schrad.) Kuhn. received the highest maximum identity scores. Although members of the Dryopteridaceae were among the best matches in a BLAST search using trnL, these results are biased since this region is currently represented by only few ferns in GenBank. Phylogenetic analyses Phylogenetic inferences of a representative set of polypod ferns for each of the single-gene data sets (rbcL and accD) were congruent. The phylogenetic relationships presented are thus based on the analyses using the combined data set. Maximum parsimony and Bayesian inference both clearly positioned the aquatic fern gametophyte within the fern genus Lomariopsis (Lomariopsidaceae), a placement that receives high branch support in the phylogenetic analyses (BSMP = 100, PPMB = 1.0; Fig. 2). Phylogenetic analyses of Lomariopsis based on the trnL–F IGS (340 nt) indicated that Lomariopsis lineata (C. Presl) Holttum is the species closest to Süßwassertang (BSMP = 96, PPMB = 1.0; Fig. 3). The trnL-F sequences from L. lineata and the aquatic fern gametophyte show a 97.6% similarity and share an 8-nt indel (Fig. 3) that is 123 80 F.-W. Li et al. Table 1 Results of BLAST searches in GenBank, with only the first ten hits shown Accessions Description Maximum score Total score Query coverage (%) E value Maximum identity (%) AB232401 Lomariopsis spectabilisa 2185 2185 98 0.0 98 AY818677 Lomariopsis marginataa 2108 2108 99 0.0 96 rbcL a DQ054517 Cyclopeltis crenata 1808 1808 99 0.0 92 AY545489 Cyrtomium hookerianum 1735 1735 99 0.0 91 AF537233 Phanerophlebia umbonata 1727 1727 99 0.0 91 AY268885 Dryopteris dickinsii 1725 1725 99 0.0 91 AY268864 Dryopteris polylepis 1725 1725 99 0.0 91 U62032.1 Matteuccia struthiopteris 1725 1725 99 0.0 91 AB232405 AB212687 accD Oleandra pistillaris 1725 1725 98 0.0 91 Oleandra wallichii 1725 1725 99 0.0 91 AB232429 Lomariopsis spectabilisa 959 959 100 0.0 96 AB232421 Polybotrya caudata 749 749 99 0.0 90 AB232442 Hypodematium crenatum 737 737 99 0.0 89 AB232433 Oleandra pistillaris 737 737 99 0.0 89 90 AB232432 Nephrolepis cordifolia 737 737 98 0.0 AB232431 Nephrolepis acuminataa 737 737 99 0.0 89 AB212687 Oleandra wallichii 737 737 99 0.0 89 AB232437 Gymnogrammitis dareiformis 732 732 99 0.0 89 AB232436 Goniophlebium persicifolium 732 732 99 0.0 89 AB212686 Arthropteris backleri 732 732 99 0.0 89 rps4-trnS AY529187 Drynaria quercifolia 479 479 89 8e-132 80 AY529189 Drynaria sparsisora 473 473 89 4e-130 80 AY529183 Drynaria descensa 473 473 89 4e-130 80 AY540049 AY529186 Lomariopsis marginataa Drynaria mollis 462 462 462 462 57 89 8e-127 8e-127 86 79 AY529181 Aglaomorpha splendens 455 455 89 1e-124 79 DQ642210 Phlebodium pseudoaureum 453 453 83 5e-124 80 AY529184 Drynaria fortunei 453 453 83 5e-124 80 AY362663 Phlebodium pseudoaureum 449 449 80 6e-123 83 DQ642221 Pleopeltis thyssanolepis 448 448 80 2e-122 83 Polystichum subacutidens 326 326 98 8e-86 78 trnL intron AY534749 AY534748 Polystichum nepalense 311 311 98 2e-81 77 AY736356 Arachniodes tonkinensis 263 263 93 6e-67 76 AY651840 Polypodium vulgare 257 257 99 3e-65 76 AF515242 Arachniodes setifera 235 235 89 1e-58 76 AF515230 Acystopteris japonica 195 195 41 2e-46 82 AF515248 Gymnocarpium oyamense 189 189 90 1e-44 74 DQ401124 DQ480129 Microsorum novae-zealandiae Woodsia polystichoides 176 174 176 174 93 44 9e-41 3e-40 74 80 AF514837 Rhachidosorus consimilis 171 171 90 4e-39 74 Lomariopsis lineataa 508 508 100 4e-141 97 trnL-F IGS DQ396572 a DQ396602 Lomariopsis sp. DQ396589 Lomariopsis pollicina 123 427 427 100 1e-116 92 427 427 100 1e-116 92 An aquatic fern gametophyte 81 Table 1 continued Accessions Description Maximum score Total score Query coverage (%) E value Maximum identity (%) DQ396587 Lomariopsis pervilleia 427 427 100 1e-116 92 DQ396576 Lomariopsis madagascaricaa 427 427 100 1e-116 92 DQ396557 Lomariopsis boiviniia 427 427 100 1e-116 92 a DQ396561 Lomariopsis hederacea 420 420 100 2e-114 91 DQ396594 Lomariopsis rossiia 409 409 100 4e-111 91 DQ396582 Lomariopsis muriculataa 409 409 100 4e-111 91 DQ396577 Lomariopsis manniia 409 409 100 4e-111 91 Sequence data of five plastid regions (rbcL, rps4-trnS, accD, trnL intron, and trnL-F IGS) were tested against GenBank entries. In total 6750 plastid sequences of monilophytes were recorded in GenBank on February 18 2008 (rbcL: 2385; accD: 162; rps4-trnS: 1052; trnL intron: 342 (2/3 Asplenium), trnL-F IGS: 482) a Members of the family Lomariopsidaceae absent in other Lomariopsis species. Despite the strong sequence similarity in the non-coding region of the chloroplast genome, the possibility for the fern gametophyte to be a different species, rather than L. lineata, could not be eliminated. Monophyly of Lomariopsis is robustly supported, in contrast to previous study by Rouhan et al. (2007). Interestingly, two hairpin-associated inversions were observed in the spacer approximately 185 nt upstream of trnF, which is different from the previously reported one for bryophytes (Quandt and Stech 2004; Quandt et al. 2004). Inversion 1 (inv 1) is homoplastic and occurs twice in: (1) L. recurvata, L. vestita, L. maxonii, and L. salicifolia as well as (2) L. amydrophlebia and L. wrigthii, whereas inversion 2 unites L. hederacea, L. muriculata, and L. manii. The distribution of both inversions in phylogenetic context is plotted on the tree in Fig. 3. Morphology of the aquatic fern gametophyte The thallus of the alleged aquatic gametophyte of Lomariopsis is ribbon-shaped, profusely branched, and onecell thick throughout, without a midrib or multicellular cushion. Rhizoids are colorless, mostly borne as marginal clusters. It grows indeterminately with active meristematic cells at the rounded apex (Fig. 1c). There are no gemmae, although small lateral branches sometimes detach from the thallus and develop as new individuals. Archegonia and three-celled antheridia are sparsely formed. These characters were also observed in the gametophytes of Lomariopsis spectabilis found in Taiwan (Fig. 1d), although they do not exactly match the strap-shaped Lomariopsis gametophytes described and illustrated by Atkinson (1973). No associated sporophyte of the Süßwassertang under study has ever been observed. Following transplantation of the gametophyte from water to soil, its growth rate was reduced, and the old portions of the thallus began to die. Unlike the gametophyte in water, rhizoids in soil-grown gametophyte were brown, and numerous antheridia formed along the thallus margins. However, sporophytes did not develop under such conditions either. Discussion The utility of different markers in identifying the mysterious gametophyte The DNA-based identification approach used here shares a similar concept with DNA barcoding, yet the latter tries to utilize more or less universal DNA barcodes. Deciding which barcode to be used for plants is still in progress (e.g., Kress et al. 2005; Chase et al. 2005, 2007; Ford et al. 2009; Hollingsworth et al. 2009). Several of the proposed DNA barcodes, such as the trnL intron (Taberlet et al. 2006), accD (Ford et al. 2009), and rbcL (Schneider and Schuettpelz 2006; Kress and Erickson 2007), were employed in this study for identifying the mysterious thallus; hence, we believe our results could provide a guideline for the future selection of plant barcodes, especially considering the situation of seedless plants. The maximum identity and E-values from the BLAST results nicely illustrate that the trnL-F IGS is more suitable for species identification in ferns than rbcL, as sequence similarity for rbcL of Süßwassertang and Lomariopsis spectabilis or L. marginata already reaches 96–98%, while sequence identity of the trnL-F IGS of both species with Süßwassertang is only 89%. In addition, the trnL-F IGS amplicon is only about 600 nt compared to 2.1 kb of rbcL and therefore easier to handle in a barcoding approach. However, as the spacer is missing in some green algae (Quandt et al. 2004) and merely reaches 60 nt in derived mosses (Quandt and Stech 2004), its use is limited. 123 82 F.-W. Li et al. Fig. 2 One of two most parsimonious trees [length 1739 steps, consistency index (CI) 0.449, retention index (RI) 0.602, rescaled consistency index (RC) 0.270] retained by the parsimony ratchet analysis performed based on the combined rbcL and accD sequence data. This tree was chosen as it perfectly reflects the Bayesian inferences. The values above the branches refer to posterior probabilities from Bayesian analysis, whereas those below the branches indicate bootstrap support values 1.0 0.96 56 0.62 98 Crypsinus enervis Gymnogrammitis dareiformis Pyrrosia rasamalae - Grammitis reinwardtii 1.0 99 1.0 0.93 1.0 - 100 98 Colysis wrightii Microsorum zippelii Goniophlebium persicifolium 1.0 Loxogramme avenia 97 Davallia formosana 1.0 1.0 100 95 Araiostegia faberiana Oleandra wallichii 1.0 1.0 100 Oleandra pistillaris 100 Tectaria phaeocaulis 69 Oleandraceae Tectariaceae Arthropteris backleri 1.0 75 1.0 1.0 99 100 1.0 Mysterious Gametophyte Lomariopsis spectabilis Lomariopsis marginata 98 Cyclopeltis crenata 0.78 82 Nephrolepis acuminata 89 1.0 88 0.84 0.96 Lomariopsidaceae Nephrolepis cordifolia 1.0 100 0.80 Davaliaceae Quercifilix zeylanica 1.0 100 0.79 1.0 Polypodiaceae - Dryopteris erythrosora Arachniodes aristata Polystichum fibrilloso-paleaceum - Ctenitis eatonii 53 Polybotrya caudata 1.0 100 1.0 0.79 97 1.0 1.0 100 81 Elaphoglossum callifolium Teratophyllum wilkesianum Dryopterdiaceae Bolbitis repanda 92 Rumohra adiantiformis 1.0 1.0 100 100 Leucostegia pallida Leucostegia immersa Hypodematium crenatum ssp. fauriei Athyrium niponicum Matteuccia struthiopteris Although more than 21,000 trnL intron sequences (bryophytes[3000, flowering plants[18,000) are recorded in GenBank, ferns are vastly underrepresented, with 342 records (on 2 February 2008), which rendered the database comparison problematic. No trnL intron sequences of Lomariopsis species or Lomariopsidaceae are recorded in GenBank, which explains why the closest matches were found among members of the Dryopteridaceae (Table 1). However, similar to the coding regions, trnL also placed Süßwassertang within polypod ferns. The reported values from BLAST searches representing sequence divergence indicate that the trnL intron resolves more relatively recent divergences compared to rbcL. Likewise, BLAST searches 123 outgroup based on the obtained rps4 (plus rps4–trnS IGS) sequence showed only 86% maximal sequence identity of Süßwassertang with L. marginata compared to 96% found for rbcL, indicating the higher potential of rps4-trnS in barcoding approaches compared to rbcL (Table 1). AccD displayed a slightly higher performance than rbcL, with 96% identity to L. spectabilis (Table 1). Therefore, if rbcL was to be chosen as the DNA barcode, a two-step approach would be favorable. With the similar concept, Kress and Erickson (2007) proposed a two-locus barcode combining trnH–psbA with rbcL for plants. This combination worked well in filmy ferns (Nitta 2008). However, trnH–psbA is absent in black An aquatic fern gametophyte 83 Fig. 3 One of 53 most parsimonious trees (length 243 steps, CI 0.774, RI 0.835, RC 0.646) retained by the parsimony ratchet analysis performed on the trnL-F IGS sequence data. The values above the branches refer to posterior probabilities from Bayesian analysis, whereas those below the branches indicate bootstrap support values. The occurrence of both observed inversions as well as two characteristic indels (5 and 8 nt) are indicated on the tree - 0.99 L. boivinii L. sp TJ2527 84 1.0 L. madagascarica 91 0.99 L. crassifolia 82 - L. pervillei - L. spectabilis - L. manii 1.0 - 87 0.92 0.94 L. muriculata 61 1.0 L. hederacea 94 L. rossii 75 2b Mysterious gametophyte 1.0 100 1.0 Mysterious gametophyte F042 96 - L. lineata - 8 nt L. cordata L. pollicina 1.0 L. sp TJ2444 100 L. sp GR318 1.0 1b 1.0 - 85 L. recurvata 1b L. vestita 1b L. maxonii 1b L. salicifolia 1b L. jamaicensis 1a L. kunzeana 1a L. amydrophlebia 1b L. wrightii 1b 89 0.53 59 0.99 76 0.59 1.0 99 5 nt 1.0 100 2a 1b 1.0 0.88 0.77 - 100 L. japurensis L. latipinna 55 L. prieuriana - L. nigropaleata - L. marginata 0.99 62 0.77 53 L. guineensis L. palustris L. longicaudata Cyclopeltis crenata Hypodematium crenatum pine (Wakasugi et al. 1994) and since two copies of trnH–psbA can be found in the Adiantum chloroplast genome (Wolf et al. 2003), a careful investigation should be done on whether multiple copies may or may not mislead species identification in ferns. Regardless of the rather conserved rbcL, Lahaye et al. (2008) proposed matK as the prime plant barcode. However, due to the rapidly evolving nature of ferns’ matK and a lack of universal priming sites, especially at the 50 end (Kuo et al., unpublished data; Wicke and Quandt, unpublished data), it would be problematic to use matK in ferns. Clearly, a comprehensive survey in seedless plants on the utility of different potential barcodes is urgently needed. 123 84 An aquatic gametophyte from an epiphytic sporophyte Fern gametophytes are well known for their extreme tolerance to environmental stresses, such as winter cold (Sato 1982), light deficiency (Johnson et al. 2000), and desiccation (Watkins et al. 2007). As a result, gametophytes in some cases were able to establish populations in sites that were probably far too extreme for sporophytes by exclusively maintaining the gametophyte generation (Farrar 1967, 1990; Dassler and Farrar 1997; Rumsey et al. 1999). Our discovery of Süßwassertang contributes another extraordinary example. Süßwassertang, originally known as a species of bryophytes, has been used to decorate fish tanks. Based on the results of our study involving DNA markers, we have identified Süßwassertang as gametophytes of Lomariopsis, an exclusively hemi-epiphytic fern clade, and found that these gametophytes have an exceptional capability to thrive in water for years without forming their sporophyte counterpart. Acknowledgment The authors thank Li-Yaung Kuo for laboratory help, Tien-Chuan Hsu for collecting Taiwanese Lomariopsis spectabilis, and Dr. Wen-Liang Chiou (Taiwan Forestry Research Institute) for valuable comments. Appendix Voucher information and GenBank accession numbersa for rbcL, accD, trnL-F and rps4 (plus rps4-trnS IGS) sequences used in this study. Part 1: rbcL and accD Taxon—GenBank accessions: rbcL, accD; voucher (collection locality; herbarium) or reference. Arachniodes aristata (G.Forst.) Tindale—AB232490, AB232418; Tsutsumi and Kato 2006. Araiostegia faberiana (C.Chr.) Ching—AB212688*; Tsutsumi and Kato 2005. Arthropteris backleri (Hook.) Mett.—AB212686*; Tsutsumi and Kato 2005. Athyrium niponicum (Mett.) Hance—AB232413, AB232441; Tsutsumi and Kato 2006. Bolbitis repanda (Blume) Schott—AB232399, AB232427; Tsutsumi and Kato 2006. Colysis wrightii (Hook.) Ching— AB232406, AB232434; Tsutsumi and Kato 2006. Crypsinus enervis (Cav.) Copel.—AB232407, AB232435; Tsutsumi and Kato 2006. Ctenitis eatonii (Baker) Ching— AB232391, AB232419; Tsutsumi and Kato 2006. Cyclopeltis crenata (Fée) C. Chr.—DQ054517?; Li and Lu 2006. Cyclopeltis crenata (Fée) C. Chr?, EU216746; F. W. Li 568 (private garden, originally from Thailand; TAIF). Davallia formosana Hayata—AB212704*; Tsutsumi and Kato 2005. Dryopteris erythrosora (D.C.Eaton) Kuntze— 123 F.-W. Li et al. AB232392, AB232420; Tsutsumi and Kato 2006. Elaphoglossum callifolium (Blume) T.Moore—AB232400, AB232428; Tsutsumi and Kato 2006. Goniophlebium persicifolium (Desv.) Bedd.—AB232408, AB232436; Tsutsumi and Kato 2006. Grammitis reinwardtii Blume— AB232398, AB232426; Tsutsumi and Kato 2006. Gymnogrammitis dareiformis (Hook.) Ching ex Tardieu and C.Chr.—AB232409, AB232437; Tsutsumi and Kato 2006. Hypodematium crenatum (Forssk.) Kuhn ssp. fauriei (Kodama) K.Iwats.—AB232414, AB232442; Tsutsumi and Kato 2006. Leucostegia immersa (Wall. ex Hook.) C.Presl—AB232388, AB232416; Tsutsumi and Kato 2006. Leucostegia pallida (Mett.) Copel.—AB232389, AB232417; Tsutsumi and Kato 2006. Lomariopsis marginata (Schrad.) Kuhn.—AY818677, NA; Skog et al. 2004. Lomariopsis sp. (Süßwassertang)—EU216743, EU216744; F. W. Li 569 (unknown origin; TAIF). Lomariopsis sp. (Süßwassertang) —AM946394?; F042 (unknown origin; SING). Lomariopsis spectabilis (Kunze) Mett.—AB232401, AB232429; Tsutsumi and Kato 2006. Loxogramme avenia (Blume) C.Presl—AB232410, AB232438; Tsutsumi and Kato 2006. Matteuccia struthiopteris (L.) Tod.—AB232415, AB232443; Tsutsumi and Kato 2006. Microsorum zippelii (Blume) Ching— AB232411, AB232439; Tsutsumi and Kato 2006. Nephrolepis acuminata (Houtt.) Kuhn—AB232403, AB232431; Tsutsumi and Kato 2006. Nephrolepis cordifolia (L.) C.Presl—AB232404, AB232432; Tsutsumi and Kato 2006. Oleandra pistillaris (Sw.) C.Chr.—AB232405, AB232433; Tsutsumi and Kato 2006. Oleandra wallichii (Hook.) C.Presl—AB212687*; Tsutsumi and Kato 2005. Polybotrya caudata Kunze—AB232393, AB232421; Tsutsumi and Kato 2006. Polystichum fibrilloso-paleaceum (Kodama) Tagawa—AB232394, AB232422; Tsutsumi and Kato 2006. Pyrrosia rasamalae (Racib.) K
H.Shing— AB232412, AB232440; Tsutsumi and Kato 2006. Quercifilix zeylanica (Houtt.) Copel.—AB232395, AB232423; Tsutsumi and Kato 2006. Rumohra adiantiformis (G.Forst.) Ching—AB232396, AB232424; Tsutsumi and Kato 2006. Tectaria phaeocaulis (Rosenst.) C.Chr.— AB232397, AB232425; Tsutsumi and Kato 2006. Teratophyllum wilkesianum (Brack.) Holttum—AB232402, AB232430; Tsutsumi and Kato 2006. Part 2: trnL-F Taxon—GenBank accessions: trnL-F; voucher (collection locality; herbarium) or reference. Lomariopsis: L. amydrophlebia (Sloss. ex Maxon) Holttum—DQ396555; Rouhan et al. 2007. L. boivinii Holttum—DQ396557; Rouhan et al. 2007. L. cordata (Bonap.) Alston—DQ396558; Rouhan et al. 2007. L. crassifolia Holttum—DQ396559; Rouhan et al. 2007. An aquatic fern gametophyte L. guineensis (Underw.) Alston—DQ396560; Rouhan et al. 2007. L. hederacea Alston—DQ396561; Rouhan et al. 2007. L. jamaicensis (Underw.) Holttum— DQ396562; Rouhan et al. 2007. L. japurensis (Mart.) J. Sm.—DQ396567; Rouhan et al. 2007. L. kunzeana (Underw.) Holttum—DQ396570; Rouhan et al. 2007. L. latipinna Stolze—DQ396571; Rouhan et al. 2007. L. lineata (C. Presl) Holttum—DQ396572; Rouhan et al., 2007. L. longicaudata (Bonap.) Holttum—DQ396573; Rouhan et al. 2007. L. madagascarica (Bonap.) Alston— DQ396576; Rouhan et al. 2007. L. mannii (Underw.) Alston—DQ396577; Rouhan et al. 2007. L. marginata (Schrad.) Kuhn—DQ396579; Rouhan et al. 2007. L. maxonii (Underw.) Holttum—DQ396580; Rouhan et al. 2007. L. muriculata Holttum—DQ396582; Rouhan et al. 2007. L. nigropaleata Holttum—DQ396584; Rouhan et al. 2007. L. palustris (Hook.) Mett. ex Kuhn— DQ396585; Rouhan et al. 2007. L. pervillei (Mett.) Kuhn—DQ396587; Rouhan et al. 2007. L. pollicina Willem. ex Kuhn—DQ396588; Rouhan et al. 2007. L. prieuriana Fée—DQ396590; Rouhan et al. 2007. L. recurvata Fée—DQ396592; Rouhan et al., 2007. L. rossii Holttum— DQ396594; Rouhan et al. 2007. L. salicifolia (Kunze) Lellinger—DQ396595; Rouhan et al. 2007. L. sp.— DQ396602; Rouhan et al. 2007. L. sp.—DQ396601; Rouhan et al. 2007. L. sp.—DQ396603; Rouhan et al. 2007. L. sp. (Süßwassertang)—EU216745; F. W. Li 569 (unknown origin; TAIF). Lomariopsis sp. (Süßwassertang) —AM946393; F042 (unknown origin; SING). L. spectabilis—EU216748; F.W. Li 567 (Wulai, Taiwan; TAIF). L. vestita E. Fourn.—DQ396598; Rouhan et al. 2007. L. wrightii Mett. ex D. C. Eaton—DQ396600; Rouhan et al. 2007. Cyclopeltis crenata (Fée) C. Chr.—EU216746; F. W. Li 568 (private garden, originally from Thailand; TAIF). Hypodematium crenatum (Forssk.) Kuhn—AF425122; Smith and Cranfill 2002. Part 3: rps4 (plus rps4-trnS IGS) Lomariopsis sp. (Süßwassertang) — AM947063; F042 (unknown origin; SING). a Asterisk, The same accession as previously noted; cross, this sequence is available in a different voucher but the same taxon; NA, data are not available for this taxon. 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