Wednesday 8 October 2014

Deep sequencing coming for three taxa at key phylogenetic nodes

Following his recent visit to Cambridge, Josh Mylne (University of Western Australia) will be collaborating with Jill Harrison (Cambridge) and Kingsley Dixon (Perth Botanic Garden) to sequence the transcriptomes of three rare taxa at key phylogenetic nodes.
Kingsley recently collected the lycophytes Phylloglossum drummondii and Isoetes drummondii and the basal angiosperm representative Trithuria bibracteata from Alison Baird Reserve, Kenwick in Western Australia this week (Figure 1).
Although lycophytes formed the dominant land plant tree flora in coal swamps that existed over 300 million years ago[1], they are now small herbs forming three distinct relict lineages[2]. Whilst club mosses such as Phylloglossum comprise c. 400 species, spike mosses such as Selaginella comprise c.700 species and quillworts such as Isoetes comprise c. 150 species.
As the evolutionary divergence of these three lineages was ancient, and the taxa sampled are rare, the new sequence data will be useful in comparative and phylogenetic studies that seek to sample densely at the base of the plant tree of life to minimize long branch artefacts.
Phylloglossum also has corms, organs with a unique ‘fuzzy morphology’ and root/shoot-like identity[3]. The new sequence data will be helpful to future evo-devo projects aiming to determine homologies.
In contrast, Trithuria comprises just 12 species and sits at a key evolutionary divergence point higher up the plant tree of life. It is an aquatic angiosperm placed in the family Hydatellaceae, one of three families in the basal angiosperm order Nymphales[4].
Trithuria differs from other water lilies in that it is tiny with narrow grass-like leaves, and the flowers may not be homologous to other angiosperm flowers, having an ‘inside out’ floral whorl arrangement[5].
Again, the new sequence data will be useful in future systematic and evo-devo studies.
To access the raw reads or de novo assembled transcriptomes when they become available please contact Josh Mylne at
Further reading
[1]            Taylor et al. (2009). Palaeobotany: The biology and evolution of fossil plants. Academic Press, Burlington.

[2]             Pryer et al. (2001). Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants.   Nature 409: 618-622.

[3]           Bower FO. 1885 On the development and morphology of Phylloglossum drummondii. Philosophical Transactions of the Royal Society of London 176:665–678

[4]             Saarela et al. (2007). Hydatellaceae identified as a new branch near the base of the angiosperm phylogenetic tree. Nature 446, 312-315.

[5]           Rudall et al. (2009). Nonflowers near the base of extant angiosperms? Spatiotemporal arrangement of organs in reproductive units of Hydatellaceae and its bearing on the origin of the flower. American Journal of Botany 96:67-82.

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