Category Archives: News

Thirsty? Then suck on a stone!

Golden gypsum crystals

Golden Gypsum Crystals from Winnipeg. Image: Rob Lavinsky/Wikimedia Commons

Whilst it is claimed that only the taxman can get blood out of a stone, it seems that some plants can abstract water from stone-like minerals.

Arguably, ahead of light, water is the most important abiotic factor that plants need and obtain from the environment. Although water is essential to plant life, it is not always available in sufficient amounts, and plants have evolved many adaptations that enable them to cope with water-limited environments – e.g. xerophytes in extremely arid areas, and halophytes in saline habitats. One strategy that was hitherto unrecognised is the extraordinary (I don’t think that’s too strong a word to use) ability of some plants to obtain large parts of their life-giving and -sustaining water from a mineral in the soil.

Analysing the isotopic composition of xylem sap in the rock rose Helianthemum squamatum, Sara Palacio et al. showed that it was similar to that of the water of crystallization in gypsum – CaSO4.2H2O, an inorganic mineral common in the plant’s environment. And, significantly, the composition of the water in the xylem differed from that of free water – i.e. that which is freely available within the soil (albeit in short supply!), the more usually assumed water source for plants. This therefore provided strong evidence that the plants were using the mineral as a water source – especially in the summer months when it accounted for 70–90% of the water used by these shallow-rooted plants.

Several other ‘coexisting shallow-rooted, sub-shrub species’ (the gypsum-specialist Lepidium subulatum – a gypsophyte – and the ‘non-specialists’ Linum suffruticosum and Helianthemum syriacum) behaved in an isotopically similar way to H. squamatum, suggesting that this phenomenon may be a widespread strategy of water-extraction by plants in this environment.

Although it is as yet unclear how the plants get hold of the water from this unusual source, it is suggested that high temperatures in the environment may cause the water to evaporate from the mineral when it can then be acquired by the plant.

Whilst this is a neat enough solution (pun recognised, but not intended!) for life on Earth, the authors conclude that ‘given the widespread occurrence of gypsum in dry lands throughout the Earth and in Mars, these results may have important implications for arid land reclamation and exobiology’. So, botanical research that may truly be ‘out of this world’!

[Intrigued by these intriguing gypsophytes? Then why not indulge your interest and read more of Sara Palacio et al.’s research in ‘Plants living on gypsum: beyond the specialist model’? – Ed.]

Classical texts re-imagined/re-imaged…

Weird Scientific Equipment

Image: Stephen Hales, Vegetable Staticks. London, W. and J. Innys, 1727.

Do you remember the good old days when students read for a degree? Well, I don’t know how much proper reading they do these days – i.e. that which involves actually touching and turning the pages of a book or research article (but which is probably nowadays forbidden on health and safety grounds – well, you never know what disease you might pick up from a multi-accessed textbook… and paper cuts can really hurt…). But if their access to the real thing is limited it is heartening to know that some classic botany/plant biology-related texts are now available online as open-access items. So, by way of whetting your – and your students’ – appetites, here are a few I’ve stumbled across (another H&S issue with piles of textbooks, journals, manuscripts in one’s room…)…

Accordingly, first mention goes to that great ‘plant physiology’ text of 1727, Stephen Hales’ Vegetable Staticks, made available by the Biodiversity History Library. That important tome investigated such phenomena as root pressure and transpiration, and made such suggestions that ‘plants very probably draw through their leaves some part of their nourishment from the air’, and speculated that plants might use light as a source of energy for growth. At the time these were ground-breaking suggestions, but the fact that we take such ideas for granted nowadays is largely due to the work of such 18th century luminaries.

Other classic texts can be accessed free courtesy of the USA’s National Library of Medicine’s (NLM) TTP (Turning The Page) Online initiative, which is itself a development of the UK’s British Library’s own TTP system. But, ‘in creating our version of TTP at NLM, we have refined the original technology by using advanced 3D computer generated imagery, digital image enhancement, animation, illumination models and software programming to simulate the act of easily flipping through virtual books displayed in a highly photorealistic manner’. To see how close this is to the real thing, you are welcome to browse such timeless classics as Robert Hooke’s 1665 Micrographia. Lauded as ‘the first scientific best-seller, inspiring a wide public interest in the new science of microscopy’ [an essential discipline for unlocking plant structure, hence physiology, etc. – Ed.], it is also notable for coining the biological term cell.

If ethnobotany is more your bag, then there’s Elizabeth Blackwell’s 1737 A Curious Herbal. This charming publication includes hundreds of colour images of plants, many drawn from London’s Chelsea Physic Garden. Drawn by Elizabeth, the illustrations are accompanied by text supplied by her medically minded husband, from his debtors’ prison cell, and before he was ultimately decapitated for international conspiracy (! I tell you, botany is so multi-faceted!). And there’s also The Edwin Smith Surgical Papyrus. Whilst it may not contain many botanic references amongst its treatments, it does at least have the great claim to fame of being the world’s oldest surviving surgical text (from approx. 17th century BCE), and was written on … papyrus (‘a thin paper-like material made from the pith of the papyrus plant, Cyperus papyrus’).

Also containing a gallery of images for each text, this NLM initiative is a lovely resource. And if it is primarily images you seek – to illustrate your teaching, etc. – then many of those in the Wellcome Images collection are now essentially copyright-free, for any usage, under a Creative Commons Attribution Only (CC-BY) licence. Wellcome Images ‘is one of the world’s richest and most unique collections, with themes ranging from medical and social history to contemporary healthcare and biomedical science’, and is of great value for providing those important historical dimensions to your lectures (and let us not forget that ‘we are where we are now because of where we’ve come from’ – Anon.), e.g. on plants-and-people or other worthy topics.

Finally, for some insight into the old-fashioned ‘world-at-your-fingertips-before-the-digital-age’, a recently completed project gives us a chance to explore the library that accompanied Charles Darwin as he travelled the world aboard the Beagle. Will all – or any – of this rekindle interest in proper books? I do hope so!

Brilliant bird-brained bryophyte diaspore diaspora…

many mosses

Ernst Haeckel, Kunstformen der Natur. Leipzig and Vienna: Verlag des Bibliographischen Instituts, 1904.
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There is an ancient and time-honoured association – maybe co-evolution even – between birds and flowering plants, e.g. in respect of pollination and dispersal of the fruits/seeds of the latter by the former. Now, at the other end of the evolutionary spectrum of the Plant Kingdom, is news of another avian–Plantae link-up as Lily Lewis et al. present evidence for long-distance transport of bryophyte ‘bits-and-pieces’ in the plumage of transequatorial migrant birds.

Bryophytes – a general term that embraces mosses, liverworts and hornworts – are so-styled ‘lower plants’ that have occupied the planet for megamillennia and have many important ecological roles. But, like the other members of the Plant Kingdom, bryophytes are essentially immobile and fixed to one location. This poses problems to any enterprising moss, etc., that wants to boldly go, seek out, occupy and colonise new areas, in order to command resources and help to ensure its survival in the dog-eat-dog jungle that is the natural world.

However, evolution has equipped these cryptogams with a phase of the life cycle that is potentially mobile, the spore stage. Transfer of those spores away from the parent plant – and their subsequent germination, establishment and development into individual bryophyte plants – reduces competition for resources between parent and offspring, and extends the area occupied by that species.

Consequently, exploiting agents that can contribute to wide-ranging dispersal of those spores represents a considerable boost to aspirations of territorial gain for an ambitious ‘lower plant’. But reliance on spores to spread the species can be risky; e.g. if the bryophyte taxon concerned is dioicous and it either doesn’t travel along with another spore that gives rise to, or to a place that already contains, the corresponding male/female gametophyte in the new neighbourhood. Which is why Lewis et al.’s work is of considerable interest because – and despite the headline in Scientific American’s news item on the subject – the bird-assisted moss migration is not really about spores, but diaspores.

Although a diaspore (or ‘disseminule’) can be defined as ‘a reproductive plant part, such as a seed, fruit, or spore, that is modified for dispersal’, the definition is usually broadened to include any plant part that could result in the establishment of a new individual. Thus, it includes not only bryophyte spores, but also fragments of established plants, too.

Sampling the plumage of bird species in their Arctic breeding grounds – prior to their South Pole-ward migration – the team found examples of diaspores not only of bryophytes, but also of green algae/cyanobacteria, and fungi. The presence of these putative propagules amongst bird feathers thus seems to establish this phenomenon as another instance of ectozoochory (transport of plant – and algae/fungi/bacteria! – propagation units on the external surface of an animal).

But just because these passengers may be present at the start of the journey doesn’t necessarily mean that they arrive at the carrier’s destination, which in some cases – such as the red phalarope and the semipalmated sandpiper – is the southernmost tip of South America; e.g. could the disseminules be consumed during preening as a sort of in-flight snack by the birds…?

And – as the investigators recognise – even if diaspores arrive, this doesn’t demonstrate that they are viable and could become established in the new home. But it’s another step towards unlocking the mystery of how the disparate bipolar distributions of certain taxa of bryophytes, etc. could be established and maintained. Whether this counts as ‘blue-skies’ research I’m not sure, but it’s a topic that’s certainly got legs and could well take off!

[And if you’re interested in seeing of some of the pre-publication comments on the bryophyte paper, they can be found online. And for more on the world of moss, I recommend Jessica M. Budke’s blog site. – Ed.]

For they are jolly good fellows

The Royal Society/Wikimedia Commons.

The Royal Society/Wikimedia Commons.

We’d like to add our words of congratulations to two recently appointed plant-biological Fellows of the Royal Society (of London for Improving Natural Knowledge), Professor Liam Dolan FRS (Sherardian Professor of Botany, Department of Plant Sciences, University of Oxford, UK) and Professor David Beerling FRS (Professor of Palaeoclimatology, Department of Animal and Plant Sciences, University of Sheffield, UK). Fittingly, Dolan has been so honoured because his ‘pivotal discoveries illuminate our understanding of the interrelationships between the development of plants, their evolution and the Earth System’ (e.g. Victor Jones and Liam Dolan, 2012Timothy Lenton et al.,  2012). Beerling has received his accolade in view of how ‘his integration of ecosystem processes into a broad geosciences framework established the importance of the terrestrial biosphere in Earth’s climate history’ (e.g. Laura Llorens et al., 2009*; Beerling, 2012). In addition to their research activities both have also taken time out to help spread the botanical message and enthuse the next generation of plant biologists, Dolan in the highly regarded undergraduate textbook Plant Biology, and Beerling with The Emerald Planet. Dolan and Beerling join approximately 1600 other Fellows in the self-governing fellowship that is the Royal Society, and which includes ‘many of the world’s most distinguished scientists drawn from all areas of science, engineering, and medicine’. Well done to these most deserving botanists!

 

* It’s also rather gratifying to think that having their work published in the Annals of Botany will have helped both gentlemen attain fellowship!

[And congratulations, too, to those UK researchers working in plant sciences (including fungi…) who’ve been named in the global Top 1%. This listing of ‘Highly Cited Researchers 2014’ names more than 3000 people selected by having writing the greatest numbers of ‘reports officially designated by Essential Science IndicatorsSM as Highly Cited Papers’. I counted four female and 11 male notables from addresses – ‘primary affiliations’ – in north, central, west and south of England, but none from Scotland (or Wales or Northern Ireland). However, I am intrigued by included scientist ‘Philip J. White’, whose primary affiliation is shown as King Saud University, Saudi Arabia (KSU), because I found no mention of this notable person on KSU’s website. So, I wonder if this could actually be the Philip J. White currently at The James Hutton Institute (Invergowrie, Scotland, UK). That P. J. White has many other affiliations – Special Professor in Plant Ion Transport at the University of Nottingham (UK), Adjunct Professor at the University of Western Australia, Visiting Associate Professor at the Comenius University, Bratislava (Slovakia), Visiting Professor of the Brazilian Research Council, and an Honorary Lecturer at the University of Dundee (Scotland) – so maybe KSU was amongst those at the time the census was taken? Or perhaps there’s been a mistake? Or there’s another Philip J. White who is even more highly cited than James Hutton’s? So, will P. J. White please get in touch and put the record straight? – Ed.]

[Ed. – we are pleased to be able to report that the mystery has now been solved. The PJ White referred to is indeed Philip White of the James Hutton Institute who is also a Professor in Biology at the King Saud University. And we are more than happy to advise that the same PJ White is a co-author on one of the Annals of Botany’s most highly downloaded papers – White PJ and Broadley MR, Calcium in plants; Annals of Botany 92: 487-511, 2003.].

Bloody royal French gourd debunked

Image: Peter Woodard/Wikimedia Commons.

Image: Peter Woodard/Wikimedia Commons.

One of the most unusual plant-based items that has come to my notice recently is this rather ‘quirky’ item that sheds a forensic botany light on an episode of ‘regicide à la française’ when King Louis XVI had an unfortunate appointment with Madame la Guillotine. Big issues of whether mere mortals have the right to execute divinely ordained monarchs and the politics of late 19th century Europe aside, what is the plant connection? It’s not the wood that may have been used to construct the fearsome ‘engine of despatch’ (a euphemism if ever there was…), the guillotine. That would be far too obvious for Monsieur P. Cuttings (although the role of plant products in execution and torture has been given a fascinating scholarly treatment by Simcha Lev-Yadun of the University of Haifa- Oranim, Israel, in his paper ‘The ancient and modern ecology of execution’).‎ Rather, it concerns a gourd (the fruit of a member of the pumpkin family, the Cucurbitaceae) – which allegedly contained a handkerchief that had been stained with blood from the ill-fated monarch. (No, I don’t know why anybody might want to do this: chacun à son gout, I guess.) A fanciful tale certainly, but nevertheless one that we might like to believe. Sadly, when the DNA of the blood was subjected to various modern-day tests and analyses by Iñigo Olalde et al. this lovely story did not stand up – much like the late king himself after his sanguine appointment – to 21st century scrutiny. In a statement as beautifully crafted as the ‘pyrographically decorated’ gourd itself, the team conclude that, ‘although we cannot totally discard that the gourd’s sample belongs to Louis XVI on our genomic data alone, several lines of evidence, including the ancestry analysis and the functional interpretation of the genome fail to provide definitive support for the attribution of this specimen to the beheaded French king’. Le fin, enfin? (c’est la vie… or mort even…).

 

[This story is reminiscent of those concerning bottles of wine bought for vast sums of money in the belief that their contents are of immense value. In those cases (pun not intended, but duly noted…) the owners apparently never drink the contents for fear of discovering that the ‘wine’ is actually worthless. Seemingly for some things it’s simply best ‘not to know’; we seem prepared to accept that some cherished beliefs may not stand up to scrutiny so we choose not to scrutinise them. After all, if we studied everything we’d know everything. Sometimes it’s just nice to leave a few ‘mysteries’… – Ed.]

Sponsor a genome…?

Image: Kurt Stüber/Wikimedia Commons.

Image: Kurt Stüber/Wikimedia Commons.

Crowdsourcing – ‘the practice of obtaining needed services, ideas, or content by soliciting contributions from a large group of people, and especially from an online community, rather than from traditional employees or suppliers’ –was the name of the game a few years ago. And in a biological context it was famously exploited to investigate protein folding using the program/‘game’ FoldIt. And so skillful have participants in this exercise become that their combined talents are now being exploited to design completely new proteins, such as new catalysts for photosynthesis.

Helping plant science we also now have crowdfunding, ‘the collection of finance from backers — the “crowd” — to fund an initiative and which usually occurs on Internet platforms’. And an intriguing example of this phenomenon is the call for funds to help sequence the genome of Azolla filiculoides by a team based at Professor Kathleen Pryer’s Seed-Free Vascular Plants laboratory at Duke University (Durham, North Carolina, USA), in collaboration with Professor Paul Wolf at Utah State University (USA). The funding opportunity is hosted by the appropriately named ‘Experiment’, a ‘platform for enabling new scientific discoveries’. Although you might expect universities to be funding the research, that has become increasingly difficult to secure and might not always be forthcoming, especially in cases of ‘risky’ projects. That’s where organisations such as Experiment, which exists to help secure funding that will allow new ideas to get off the ground, especially ‘the innovative and high-risk ideas with the biggest impact’, come into their own. Acting primarily as a shop window, Experiment advertise projects to would-be sponsors – who in true egalitarian style can be anybody, true citizen science in action – and only charge a fee for their services when the project becomes fully funded. And at 8% of the funding total secured that fee is much lower than normal university overhead charges, which take large shares of research funding provided by more traditional sources such as government-funded research organisations!

Anyway, back to the Azolla project. The modest sum of US$15 000 is sought to generate a draft sequence of the genomes of Azolla and its symbiotic N-fixing bacteria, with a view to understanding the two-way, inter-kingdom language that codes for the molecular machinery underlying this symbiotic partnership, and possibly tailor it to suit our needs. Why? Azolla is a ‘superorganism’, consisting of not just the fern but also a diverse array of symbiotic bacteria. It is this unique microbiota that converts nitrogen into organic forms and makes Azolla a perfect bio-fertilizer. In a world where we are ever more concerned about pollution by increasing use of synthetic fertilisers to increase crop yields to meet an increasing demand for food by a growing human population, you might think that this is the sort of project that should be funded by tax dollars extracted from the populace by governments, rather than expecting their already-taxed citizenry to dig into their own pockets effectively twice over. But it always pays to look at the fine print: ‘Genomic sequencing of this unique Azolla–Nostoc system would cost well under $1 million’. Whilst $15k is well under $1 million, I suspect the final figure required will be much closer to $1 million than $15k, which I guess is what’s hinted at behind the text ‘as a start, the funding of $15 000 will get us reasonably good quality genomes [P. Cuttings’ emphasis] for the Azolla superorganism that can jumpstart various exciting research programs’ in the project’s ‘budget overview’. Maybe more traditional sources of funding will pick up the remaining US$985 000 if the project’s potential is demonstrated on the shoestring budget? If only because, although approximately US$1 million is considerably more than the $15 000 sought, that’s ‘far less than the $8 billion each year that US farmers pay for nitrogen fertilizer’ – much of which finds its way into rivers and streams, damaging delicate water systems. This small step toward potentially helping crops to use less synthetic nitrogen could benefit farmers’ bottom lines, the environment and the prices we pay for food’. Hear, hear! And as I write this on 9th June 2014 there are 32 days left to pledge and add to the then-current total of US$1625. Good luck securing the rest of the funding!

[What we haven’t got space to go into here – but which also emphasises another unique characteristic of Azolla – is the role it played in global cooling in the Arctic Azolla Event of 50 million years ago. A famously fascinating fern, indeed! – Ed.]

[Ed. – by way of follow-up to the above story, we are pleased to learn that BGI (formerly the Beijing Genomics Institute, but now based in Shenzhen) has now supported the Azolla genome project by offering to fulfill all of the necessary sequencing needs free of charge. For an insightful article dealing with the crowdsourcing initiative, and lessons learned therefrom,  see Li and Pryer: Crowdfunding the Azolla fern genome project: a grassroots approach. GigaScience 2014 3:16; doi:10.1186/2047-217X-3-16.]

Clear way ahead for leaf research

Image: Benjamin Blonder/Cleared Leaf Image Database.

Image: Benjamin Blonder/Cleared Leaf Image Database.

Databases (collections of information that are organised ‘so that it can easily be accessed, managed, and updated’) are everywhere these days and, as repositories of data that can be explored by interested parties – and maybe new connections made and insights revealed – they are an extremely useful resource for science. Indeed, access to large data sets is so important to modern-day scientific endeavour that a new journal has recently been established to publish the outcome of such studies. Scientific Data is an open-access, online-only publication for descriptions of scientifically valuable datasets that exists to help you publish, discover and reuse research data and will ‘complement and promote public data repositories’. And in the tradition of science belonging to us all, the journal’s primary article type, the ‘Data Descriptor’, is designed to make your data more discoverable, interpretable and reusable. However, for such journals to achieve their noble and philanthropic aims, the necessary databases of ‘stuff’ need to exist – or be created. One such facility whose birth caught my eye(!) recently was the ClearedLeavesDB, an online database of cleared plant leaf images – its existence and purpose has been highlighted by Abhiram Das et al., who developed it. Leaf vein networks (LVNs) are important to both the structure and function of leaves and there is a growing body of work linking LVN structure to the physiologyecology and evolution of land plants. Recognising the importance of LVNs, the team developed this digital archive that enables online viewing, sharing and disseminating of collections of images of cleared leaves (which usually have the LVNs enhanced) held by both institutions and individual researchers. We applaud this initiative and trust that its objectives – to facilitate research advances in the study of leaf structure and function, to preserve and archive cleared leaf data in an electronic, accessible format, and to promote the exchange of new data and ideas for the plant biology community – are met.

M people and the ‘B’ word…

Image: Wikimedia Commons.

Image: Wikimedia Commons.

No, this is not an item about M People, an ‘English house music band which formed in 1990 and achieved success throughout most of the 1990s’, nor about using profane language… Anyway, how would any of that be relevant to a straitlaced, sober, serious botanical news round-up that is the hallmark of a P. Cuttings item? It is about the phenomenon (I don’t think that’s too strong a word) known as ‘Dr M’. If you’ve not encountered this gentleman, then you should – we can probably all learn a little from him in our eternal quest to big-up botany and help to enthuse the next generation of plant biologists (or, at least, attempt to engender plant appreciation into the citizens of tomorrow). Dr M is the moniker of Dr Jonathan Mitchley, botanist and plant ecologist who goes WILD about teaching plant identification at the University of Reading (UK), and also acts as an ecological consultant with RSK Ltd. Looking like one imagines the Peter Pan of phytology should look like, his grinning visage beams botanical radiance upon all who chance upon his various web-based antics. His enthusiasm for all things verdant seems boundless and is evident in his varied offerings, such as his blogvideo-based plant ID quizzes and his YouTube-tastic Poaceae song. Maybe all of his outputs may not be to everyone’s taste, but they’re worth a look – you are highly likely to find something you can ‘borrow’ to enhance your own teaching of botany. In any event it’s really uplifting to see Dr M and ‘his people’ having so much botanical fun! As Dr M himself is wont to say, ‘Rock on, Botanists!!!’ Indeed (!).

 

[The true diehards amongst you might like to consider the extended-play, blooper-enhanced version of the Poaceae song on YouTube. Right, now what is the collective noun for a group of botanists? Answers, on a postcard-sized sheet of herbarium paper, please to… And in breaking news – well it was when this piece was penned – Dr M is now Associate Professor of Field Botany at the University of Reading – Ed.]

Deep sequencing coming for three taxa at key phylogenetic nodes

Following his recent visit to Cambridge, Josh Mylne (UWA) 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 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.

Lycophytes from the Alison Baird Reserve.

Isoetes drummondii (A,D), Phylloglossum drummondii (B,E) and Trithuria bibracteata (C,F) collected from the Alison Baird reserve.

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 joshua.mylne@uwa.edu.au.

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. doi:10.1038/35054555
  3. Bower FO. 1885 On the development and morphology of Phylloglossum drummondii. Philosophical Transactions of the Royal Society of London 176:665–678. doi:10.1098/rstl.1885.0012
  4. Saarela et al. (2007). Hydatellaceae identified as a new branch near the base of the angiosperm phylogenetic tree. Nature 446, 312-315. doi:10.1038/nature05612
  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. doi:10.3732/ajb.0800027