Invisible in plain sight: Recurrent double allopolyploidy in the African Sphagnum ×planifolium (Sphagnaceae)

Microsatellites, nucleotide sequences, and flow cytometry were used to determine if two sympatricAfrican peat mosses (Sphagnum ×planifolium and S. ×slooveri) had a history of inter-subgeneric hybridization and to assess their phylogenetic relationship. Both species had previously not been considered to be hybrids. Sphagnum ×slooveri was found to be gametophytically allodiploid. Its maternal parent was S. recurvum (or a closely related species) of subg. Cuspidata and its paternal parent was an unidentified species from the S. africanum complex of subg. Subsecunda. Sphagnum ×planifolium was found to be a cryptic species complex of gametophytic allotriploids, with recurrent double allopolyploidy resulting in at least two evolutionarily distinct lineages. The maternal parent of both lineages was S. ×slooveri. The paternal parent of one lineage (S. ×planifolium I) was an unidentified haploid associated with the S. capense complex of subgenus Subsecunda while the paternal parent of the second lineage (S. ×planifolium II) was S. cuspidatum (or a closely related species) of subg. Cuspidata. Four species having a history of double allopolyploidy are now documented in bryophytes; all are gametophytically allotriploid, all are in Sphagnum, and all had an allodiploid parent having a history of inter-subgeneric hybridization. It is postulated that a high genetic divergence between subgenomes may facilitate double allopolyploidy in Sphagnum. Genetic analyses reveal that S. pulchricoma, S. recurvum and S. sancto-josephense form a complex of non-hybrid and hybrid plants in the Neotropics, with the hybrids having a history of hybridization between S. cuspidatum and S. recurvum. Reticulate evolution needs more attention in bryophyte studies and this requires experimental designs sufficiently robust to detect it. © 2014 The American Bryological and Lichenological Society, Inc.

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Author A. Jonathan Shaw Biology