The Tree Fern Tree
If I gave you a tree fern right now, would you know if I gave you the beautiful Cyathea cooperi or the addicting Dicksonia antarctica? Perhaps it might help if you knew how tree ferns were classified?
DNA data suggests that tree ferns are monophyletic (Hasebe, 1994), which means they all share a common ancestor and constitute a single “frond branch” on the “tree fern of life”. The tree fern order is known by botanists as Cyatheales. They branched away from other core lineages around 220 million years ago (Pryer et al. 2004) making these plants old enough to receive the pension.
In the above “Tree Fern Tree” I have highlighted the core tree fern clade in a green box. Please take a moment to familiarise yourself with that clade as that is the focus of today’s post. Do you recognise which two genera have been mentioned already in previous posts?
So when I hand you a tree fern, the first thing I would recommend you look for are hairs or scales on the fronds. Hairs are thin cells stacked end to end (Large & Braggins, 2004), while the scales appear more like flat fur. If it has scales, it will be a Cyathea species (Large & Braggins, 2004). Let’s say it has hairs, so it must either be a Dicksonia, or a Cibotia. How can we tell these two apart?
You must now look at the sori, the sporangia clusters. Both Dicksonia and Cibotia will have bilobed sori on the margins of their leaves. Cibotia sori will have lobes that are identical in texture and colour, unlike Dicksonia, in which the lobes are dissimilar (Large & Braggins, 2004). If I clumsily gave you a Cyathea by mistake, you would notice straight away that it has abaxial sori, meaning the sori are located around the middle of the leaf, not at the edges. Obviously I would appolagise for this mistake, saying “sori about the mix up”.
Regardless of what tree fern I give you, it almost certainly won’t be a Metaxya which consists of only a single genus and two species with a creeping rhizome (Cardenas, 2016). Genetic data confirmed that Metaxya has a close relationship to Cyathea and Dicksonia (Hasebe, 1994) and that is why it is included in this clade. Just between you and me (and the internet) I consider Metaxya to be somewhat embarrassing, they don't even have a trunk!
But what about those other purple and yellow clades? we will look at those in future posts. Until then, keep your trunk wet.
Reference list
Cárdenas, G.G., Tuomisto, H. & Lehtonen, S. 2016, "Newly discovered diversity in the tropical fern genus Metaxya based on morphology and molecular phylogenetic analyses", Kew Bulletin, vol. 71, no. 1, pp. 1-27.
Hasebe, M., Omori, T., Nakazawa, M., Sano, T., Kato, M. & Iwatsuki, K. 1994, "rbcL Gene Sequences Provide Evidence for the Evolutionary Lineages of Leptosporangiate Ferns", Proceedings of the National Academy of Sciences of the United States of America, vol. 91, no. 12, pp. 5730-5734.
Large, M.F. & Braggins, J.E. 2004, Tree ferns, CSIRO Publishing, Collingwood, Victoria.
Pryer, K.M., Schuettpelz, E., Wolf, P.G., Schneider, H., Smith, A.R. & Cranfill, R. 2004, "Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences", American Journal of Botany, vol. 91, no. 10, pp. 1582-1598.
Smith, A.R., Pryer, K.M., Schuettpelz, E., Korall, P., Schneider, H. & Wolf, P.G. 2006, "A classification for extant ferns", Taxon, vol. 55, no. 3, pp. 705-731.
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| A painting of a tree fern forest http://www.kentcrawford.ca/wp-content/uploads/2016/08/treeferns_sk_2016_1000x634_tgf.jpg Viewed on 12/4/18 |
DNA data suggests that tree ferns are monophyletic (Hasebe, 1994), which means they all share a common ancestor and constitute a single “frond branch” on the “tree fern of life”. The tree fern order is known by botanists as Cyatheales. They branched away from other core lineages around 220 million years ago (Pryer et al. 2004) making these plants old enough to receive the pension.
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| Phylogenetic Tree of Cyatheales. Image produced by Dale Perkins on 12/4/18 based on the article "A classification for extant ferns" by Smith, Pryer, schuettpelz, Korall, Schneider and Wolf which can be found in the reference list. |
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| The hairs on a Dicksonia frond https://commons.wikimedia.org/wiki/File:Dicksonia_antarctica_2.jpg Viewed 12/4/18 |
You must now look at the sori, the sporangia clusters. Both Dicksonia and Cibotia will have bilobed sori on the margins of their leaves. Cibotia sori will have lobes that are identical in texture and colour, unlike Dicksonia, in which the lobes are dissimilar (Large & Braggins, 2004). If I clumsily gave you a Cyathea by mistake, you would notice straight away that it has abaxial sori, meaning the sori are located around the middle of the leaf, not at the edges. Obviously I would appolagise for this mistake, saying “sori about the mix up”.
 | ||
| The scales on a Cyathea frond https://pixabay.com/en/koru-native-tree-fern-plant-frond-1091917/ Viewed 12/4/18 |
Regardless of what tree fern I give you, it almost certainly won’t be a Metaxya which consists of only a single genus and two species with a creeping rhizome (Cardenas, 2016). Genetic data confirmed that Metaxya has a close relationship to Cyathea and Dicksonia (Hasebe, 1994) and that is why it is included in this clade. Just between you and me (and the internet) I consider Metaxya to be somewhat embarrassing, they don't even have a trunk!
But what about those other purple and yellow clades? we will look at those in future posts. Until then, keep your trunk wet.
 | |
| A tree fern from above https://commons.wikimedia.org/wiki/File:Tree_Fern_at_Kew_Garden_(Steve_Parker).jpg Viewed on 12/4/18 |
Reference list
Cárdenas, G.G., Tuomisto, H. & Lehtonen, S. 2016, "Newly discovered diversity in the tropical fern genus Metaxya based on morphology and molecular phylogenetic analyses", Kew Bulletin, vol. 71, no. 1, pp. 1-27.
Hasebe, M., Omori, T., Nakazawa, M., Sano, T., Kato, M. & Iwatsuki, K. 1994, "rbcL Gene Sequences Provide Evidence for the Evolutionary Lineages of Leptosporangiate Ferns", Proceedings of the National Academy of Sciences of the United States of America, vol. 91, no. 12, pp. 5730-5734.
Large, M.F. & Braggins, J.E. 2004, Tree ferns, CSIRO Publishing, Collingwood, Victoria.
Pryer, K.M., Schuettpelz, E., Wolf, P.G., Schneider, H., Smith, A.R. & Cranfill, R. 2004, "Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences", American Journal of Botany, vol. 91, no. 10, pp. 1582-1598.
Smith, A.R., Pryer, K.M., Schuettpelz, E., Korall, P., Schneider, H. & Wolf, P.G. 2006, "A classification for extant ferns", Taxon, vol. 55, no. 3, pp. 705-731.
It's about time you used the "sori" pun
ReplyDeleteHahaha I've been saving it for a sunny day!
DeleteThis was very intriguing blog. You depict the green clade on your diagram as a polytomy. Does this mean that the relationships between these four groups is unresolved?
ReplyDeleteHi Tasmin
DeleteI couldn't talk much about the unresolved relationship without producing something that resembled a novel, but I can sum it up by saying that tree ferns are fairly complicated. Let's just use "Metaxyaceae" as an example. When analysed with Maximum Parsimony (MP) Metaxyacea appears to be a sister group to all other tree ferns. Yet when you use a model based system (M/MCMC and ML) Metaxyaceae appear to be a part of the core tree ferns (Korall et al, 2006). In the end I chose to use the Smith tree because it looked at the phylogeny of all leptosporangiates (for which Cyatheales falls under) making the paper more applicable to the wider fern community, but also, the smith article was was coauthored with tree fern experts such as Korall.