Plant Lives: A timely coincidence

Plant Life: A Brief History. Frederick Essig. Oxford University Press, 2015

A phenomenon I thought only applied to buses was that you wait for ages for one of them to arrive and then two turn up together. Well, a similar thing has happened recently in the world of plant biology book publishing. The two tomes are Armstrong’s How the Earth Turned Green: A brief 3.8-billion-year history of plants * and the one I write about today, Essig’s Plant Life: A brief history (hereafter referred to as Plant Life). That’s not a problem, merely an observation. Hey, I like books about plants so I am definitely not complaining! But what also struck me about these two is how similar they are (but more on that later).

Technical stuff: Plant Life’s 261 (+ xv) pages are principally spread across an Introduction, 9 numbered chapters, an Epilogue, Endnotes, Glossary, Bibliography, and Index.

What is Plant Life all about?

Short answer: It’s ALL about plants (particularly the evolution of land-plants [‘proper’ plants…] from their non-plant photosynthetic progenitors).

Long(er) Answer: …

Assessment of Plant Life

Essig has done a great job in retracing almost 4 billion years of evolution (and – Creationists be warned! – Plant Life has a strong and clear evolutionary dimension) that has resulted in the plant life with which we share the planet today. But, not only that, Plant Life is also well written – right from the first page of chapter 1. So, whilst it has the educational value of a textbook (and each of the chapters could easily be used as the basis of a lecture – or several in some cases!), it is eminently readable. And sufficiently endowed with in-text citations to permit one to follow-up points of interest in the literature.

Indeed, approx. 50% of the book’s 100+ references are dated post-2000, and at least 6 have 2013 or 2014 publication dates, which attests to its up-to-dateness (and given both Plant Life’s subject matter, and a recognition of the evolution of ideas regarding plant evolution, many references are of necessity older than one might expect in a modern-day textbook to give that important historical dimension).

Pleasingly, there are only approx. two pages of Notes – to supplement material within the body of the text – which is nice and few and means that matters of explanation are generally where they belong, within the text with the relevant material. And where it is not possible to explore a topic in more depth (a book – even a textbook – must be of a manageable/marketable length, after all…), Essig indicates and cites relevant reviews, e.g. Niklas (1997) re modes of nutrition, Zimmer (2009) on sexual reproduction, and Raven and Edwards (2001) re roots.

Although there are no colour images within the text [because that would have been too expensive for the scale of the project – p. xi], Essig has sidestepped that criticism in seeking to showcase the botanical line art tradition “with some of the best line art ever published” (p. xi). Whilst many of those images are effective in achieving that goal, the lack of scale bars can be a little irritating from a pedagogic point of view. And, for die-hard, botanicochromaphiles, there are some colour images on the front cover (thought they aren’t the most inspiring trio one can imagine…).

Whilst Charles Darwin’s angiosperm “abominable mystery” [and for more on the real meaning of this phrase, see Friedman (2009)], is used almost as a starting point for the book (Introduction, p. xiii), you know that Plant Life is not going to be the last word on the subject of plant evolution because Essig is quick to point out the many other plant mysteries that remain, e.g. the origins of photosynthesis (and of life itself…), the origin and early evolution of land plants, and the origins of the first plants with seeds, etc. Notwithstanding the fact that there are so many unknowns, which leads one to wonder why anybody would attempt to offer any sort of synthesis, it is important to start somewhere, if only to be able to recognise the gaps where more information is needed. Accordingly, Plant Life attempts to deliver what one would like to think is the current consensus view of ‘how plant life came to be’, and does so in 9 chapters that provide a sequential appreciation of the development of plant complexity. And throughout, Plant Life is suffused with much of educational value for sharing with one’s students (and for one’s own edification!).

Thus, Chapter 1 starts the journey with a consideration of The origins of photosynthesis wherein Essig makes the point that ‘plants’ are Earth’s primal planet-dwellers; animals could not exist until there were oxygen-producing photosynthetic plants to supply the former’s need for oxygen. And thereby any argument about whether plants or animals are more important is nipped in the bud straightaway! For those of use struggling to summarise the light reactions of photosynthesis in text, a lot can be learnt from pp. 6-12, and a good introduction to the importance of HGT [horizontal gene transfer, a process unknown to Darwin but which has had a powerful influence on evolution] is gleaned from its relevance to photosynthesis wherein two HGT events are considered.

In Ch. 2 Eukaryotic plant life, endosymbiosis is covered with a timely reminder that – important though Margulis’ contribution was – this notion is not due to Lynn Margulis et al. in the 1970s, but was apparently first proposed in 1905 by Russian Botanist Konstantin Mereschkowski, who had a somewhat ‘colourful’ history and end-of-life (and the concept can even be traced back to 1883 and the French Botanist Andreas Schimper). Now, whilst I was aware that chloroplasts had two membranes (which indicates their primary endosymbiotic origin), that strictly only applies to the chloroplasts of green algae and land plants and red algae, those of brown algae, diatoms, euglena, and dinoflagellates are triple-membraned (!)(which is evidence of secondary symbiosis), and there are apparently some dinoflagellates whose chloroplasts have four membranes indicating a tertiary symbiosis(!!).

Ch. 3 Plants invade the land (though shouldn’t this be ‘algae’ invade the land..? Discuss!) contains the rather sobering thought – for one who firmly believes in the superiority of plants over all other lifeforms – that the first terrestrial organism was not necessarily a land plant progenitor but more likely a desiccation-tolerant bacterium in wet or intermittently wet places, and the first multicellular land organism was probably a … fungus. In many respects this chapter covers the ‘familiar’ story of the challenges posed by invasion of/living on the land with appropriate mentions of cuticle, stomata, vascular tissues, and alternation of generations (but it’s a tale always worth a retelling, and is essential to the evolutionary narrative of the book). We are also introduced to the concept of a ‘penguin strategy’ for moss survival, and the notion that mutations in master regulatory genes act as pivotal moments in plant evolution, e.g. re spores’ desiccation-resistant cell wall, and sporophyte branching, and the chapter concludes with thoughts on ‘why mosses are small, and trees are tall’.

Ch. 4 Vascular plants and the rise of trees covers the ‘race to the sky’ which began in the Devonian and took only 60 million years to produce proper trees and forests from plants just a few cm tall, and whose tall stems and deep root systems changed the earth (in both senses of the word!) dramatically; e.g. in accelerating the development of soil, creating more complex freshwater recycling patterns, and converting CO₂ into biomass (some of it still being exploited in fossil fuels today…).

Ch. 5 Seeds and the gymnosperms – not just seeds, but pollen as well, with a consideration of whether early gymnosperms were wind- or insect-pollinated. Yes, it is a great shame to summarise that chapter with so few words, so do visit it yourselves(!)

Ch. 6 Darwin’s abominable mystery – in which ‘wet and wild’ and ‘dark and disturbed’ hypotheses of angiosperms’ origins are introduced, and there is the cherished-notion-destroying moment when one learns that angiosperms per se evolved before flowering plants so the two terms aren’t necessarily synonymous(!). As befits a section on the flowering plants, there is lots of discussion and consideration of floral structure, and much emphasis on the vagaries of the fossil record in considering the origins of angiosperms (and thereby setting out the case for a need for subsequent editions of Plant Life when newer, missing-link’ fossils are discovered..?).

Ch. 7 Adaptations for pollination and seed dispersal. If the book – and its plant evolution story – was a game of chess, this chapter could be considered the beginning of the end-game, for here are considered two of Stebbins’ important plant adaptational pressures (see p. 52): sexual union, and dispersal of reproductive units that culminate in nature’s crowning glory, the flowering plants. And this section shows just how far angiosperms have come since their early experiments with beetles as pollen-ferrying go-betweens. Colour, smell, food, even heat have all successfully been exploited by plants who thereby manipulate and manage the behaviour of unsuspecting animals whose own needs are subverted by the reproductive desires of plant. Appropriately, all manner of contrivances and zoophilic relationships are surveyed in this interesting chapter. And we are also introduced to some of the author’s botanical specialisms with mention of weevil-pollinated Costa Rican palms Bactris spp. and Papua New Guinean Hydriastele. And, re Nypa pollination, there’s an insight into the activities of a field botanist, and a reminder – albeit tongue-in-cheek – of the debt of gratitude that the world owes Essig. Herein too, the pollination activities of fig-wasps are described (including a welcome reminder that cultivated figs produce fruit without pollination so vegetarians need not fear that they are getting a mouthful of dead wasps when they eat theirs). In addition to these ‘accidental’ pollination phenomena, Essig provides an – the? – example of deliberate pollination by the yucca moth. As well as biotic agents of pollination, this chapter also deals with wind- and water-pollination, and has 6.5 pp. related to fruit and seed dispersal. [It’s also pleasing to see cotton – the material derived from the plant of the same name that is converted to fabric – properly described as tufts of hairs (not fibres as it is so often incorrectly stated, even in botany texts!)] In abbreviated encyclopaedic style, this review of angiosperm diversity provides an important sexual/reproductive dimension to the more vegetative one covered in chapters 8 and 9.

Ch. 8 The dicotyledonous grade – highly-evolved plants united by flexible forms of leaf development and which display great variety of growth forms from giant woody trees to tiny aquatic herbs (and almost everything in between…). Accordingly, this chapter includes trees, annuals and biennials, clonal trees, perennial herbs, vines, aquatic plants (a lifestyle ‘discovered’ independently in many unrelated eudicots [dicots is no longer an acceptable term…] and monocots, and water-lilies), and leaves (lots about leaves and their modifications – e.g. bracts, tendrils and spines, deciduous leaves, and xerophytes (and where CAM [Crassulacean Acid Metabolism] is mentioned, but in a way that is very light on the biochemical details thereof)). And there’s a very good consideration of carnivorous plants (the ultimate example of dicot leaf plasticity) – a syndrome that probably evolved independently at least 6 times amongst plants – in which Essig traces the putative steps along the evolutionary paths that led to proper, full-blown carnivory. Something that had passed me by in this context was the revelation that Genlisea traps protists [“eukaryotes that are not plants, animals or fungi” – p. 22] in its underground leaves (so-called ‘lobster-pot traps’). However, Essig’s assertion that this – from Barthlott et al. (1998) – is the “most recently verified carnivorous plant” is surely contradicted by work of Pereira et al. (2012) that attributes carnivorous behaviour to the underground leaves of Philcoxia which trap and digest nematodes. And, although this is a dedicated dicot chapter, for some sort of completeness, it would have been nice to see at least mention that carnivory has been proposed in bryophytes, such as the liverwort Pleurozia purpurea (Hess et al., 2005). Nevertheless, although only 4 pages of Plant Life are devoted to carnivorous plants, this is still quite a serious chunk of the entire book. And, why not? After all, there are “quite a few reasons for calling carnivores ‘the most wonderful plants in the world’” (Król et al., 2012). Finally, this chapter also considers secondary plant compounds (SPCs). Having invested significant evolutionary capital in developing many and varied ways and contrivances to attract insects for pollination, plants do have to defend themselves from the unwanted trophic attentions therefrom, hence development of SPCs. And, although only occupying a single page, Essig is careful to remind us of the importance of SPCs to humankind in terms of food flavourings and medicines.

Ch. 9 The Monocots: an extremely highly-evolved group of flowering plants that are characterised by a much more restricted development plan than dicots – and one which prohibits wood – but which excel at surviving underground. Whilst consideration of monocots is not exclusively restricted to this chapter – it is difficult to consider groups such as dicots elsewhere in the book without contrasting them to monocots – this represents an opportunity to explore and celebrate monocot diversity and specialisation in one dedicated place. Since we tend to hear more about dicots when flowering plant diversity is considered, it is refreshing to have a whole chapter devoted to monocot diversity. So what is included? The monocot leaf (which, contrary to what one might have imagined, does include true compound leaves such as the palms’), and monocot stem, geophytes, epiphytes, and xerophytes (with a – slightly! – more biochemical mention of CAM than we had in chapter 8), arborescent palms [with a reminder of why the stems of such plants are ± the same diameter from bottom to top, cf. dicot trees, and are also often stronger than their dicot counterparts as some can withstand being bent down to the ground in strong winds yet bounce back seemingly undamaged], not forgetting the persistence and resilience of the grasses, and aquatics (not only in freshwater but submarine spp. too!) And there is the revelation that palm trees contain the longest-lived plant cells, which may be active for several hundred years (!). Let’s hear it for the monocots!!!

Thus, the book’s extraordinary journey ends with the monocots, “a group of plants that have come to dominate many habitats of the Earth through a unique and specialized, but highly versatile, architectural plan… whose superiority as clonal plants in stressful and extreme environments points to them as a major cutting edge in plant evolution” (p. 229). And that ultimate accolade is fitting because it is the monocots – as providers of cereals amongst the grasses – that have largely fuelled humankind’s own recent evolution and development with the advent of cereal-based agriculture.

Comparisons?

Although quite a lot of the material covered in Plant Life can be found in standard Botany or plant biology textbooks, it probably either won’t be in a single place or as complete an evolutionary history of plant life as provided by Essig. Those texts are therefore not a good comparison for Plant Life. Rather, Plant Life‘s obvious comparison is with Armstrong’s How the Earth Turned Green: A brief 3.8-billion-year history of plants. And the two compare extremely well; e.g. they cover the same story and timescale, neither includes colour images, both include references for follow-up (with varying degrees of in-text referencing), and both demonstrate high degrees of pedagogy, etc. The main difference is in narrative style. Although both are highly readable – and show how readable ‘textbooks’ can – and ought to? – be, Armstrong’s is the more ‘idiosyncratic’ (but in a good way!) whilst Essig’s is a little more formal/traditional. Both contain information or interpretations that the other doesn’t, together therefore they give a very comprehensive view of the present-day understanding of how the land flora came to be.

Quibbles…

I have a few quibbles, which are largely from the point of view of using Plant Life as a student text (which, whilst it may not be the author’s declared categorisation of the book, is how I’ve chosen to assess it). Whilst it’s good to see references integrated into the text, it would help to instil good practice in students if the references for cases of multiple citations are shown in chronological order – oldest first. This is not done on p. 1 (though is correct re pp. 4, 68, 224…). On p. 5, ATP and NADPH are first mentioned solely in those abbreviated forms. Whilst the ATP initialism is defined in the Glossary (p. 238), and in the text – eventually! – on p. 9, the NADPH initialism is neither defined in the Glossary (p. 242), nor – apparently – elsewhere in the text; it needs to be spelt out for completeness. There is an opportunity for confusion on p. 9 where a paragraph begins thus “Making ATP … adding a phosphate unit to … ADP … is called cyclic photophosphorylation”. Well, technically what’s been stated in that sentence is just phosphorylation, explicit involvement of light is required for it to be categorised as photophosphorylation. But as stated it’s neither cyclic nor non-cyclic, that distinction will depend upon which photosystems are involved in the light-driven process in the chloroplasts. In the context of the preceding text, it’s probably the non-cyclic variant that was dealt with, anyway. Another questionable statement is that the aquatic carnivorous plant Utricularia creates partial vacuum in its underwater traps “by pumping water out osmotically” (p. 191). Pumping doesn’t sound like osmosis – passive diffusion of water – to me. And, whilst one understands the sentiment behind the statement on p. 217 that photorespiration is the phenomenon in which carbohydrates produced by photosynthesis are “burned up on the spot with no apparent benefit”, it’s probably a little misleading since there are several pieces of research that suggest the process is beneficial [e.g. Peterhansel and Maurino (2011); Bauwe et al. (2012)], and the notion of ‘burning carbohydrates’ is rather economical with the biochemical details of the phenomenon. Probably less defensible is the idea that stromatolites have been around for about 3.5 million years (p. 1); I really think that this should be 3.5 billion years. And Araliaceae is not the proper name for the carrot family (as stated on p. 225), that honour goes to the Apiaceae. Finally, should one overlook the use of the noun form of the word ‘practice’ where the verb – with a penultimate ‘s’ not a ‘c’ – form is surely meant (on pp. 6, 15, and 19)? Or the misspelling of understorey as understory on p. 208? Apparently, yes, we should; both spellings are ‘Americanisms’ of the English language we probably have to accept in today’s global – albeit heavily Americanocentric – village.

Overall view

But let’s not end with the book’s ‘economical truths’ or dwell on its ‘errors’ (some of which are probably inevitable when a specialist tries to deal with such a vast, general topic as plant evolution, and were pleasingly few as far as this physiological plant anatomy-specialist reviewer could tell anyway…). Instead, let us conclude, as the Epilogue rightly does, that in its nine numbered chapters Plant Life has shown sequentially how distinctive features of plant life evolved as various environmental challenges were overcome and opportunities capitalised upon. And what a story! I never tire of reading it (there were lots of insights in Essig’s ** tale that I don’t recall from Armstrong’s), and am frequently surprised by new interpretations or instructional points that I can share with my own students. And such a story – and book – deserves to be shared!

* If you’re interested in my assessment thereof, see https://botany.one/2015/06/how-the-earth-turned-green/

** For more botanical musings and insights by Associate Professor Emeritus of Biology at the University of South Florida, Frederick Essig, visit his blog at http://botanyprofessor.blogspot.co.uk/

References

Armstrong JE (2014) How the Earth Turned Green: A brief 3.8-billion-year history of plants. The University of Chicago Press.

Barthlott W, Porembski S, Fischer E and Gemmel B (1998) First protozoa-trapping plant found. Nature 392: 446-446.

Bauwe H, Hagemann M, Kern R and Timm S (2012) Photorespiration has a dual origin and manifold links to central metabolism. Current Opinion in Plant Biology 15: 269–275.

Friedman WE (2009) The meaning of Darwin’s “abominable mystery.” American Journal of Botany 96: 5–21.

Hess S, Frahm J-P, Heisen I (2005) Evidence of Zoophagy in a Second Liverwort Species, Pleurozia purpurea. The Bryologist 108(2): 212-218.

Król E, Płachno BJ, Adamec L, Stolarz M, Dziubińska H and Trębacz K (2012) Quite a few reasons for calling carnivores ‘the most wonderful plants in the world’. Annals of Botany 109: 47–64.

Niklas K (1997) The Evolutionary Biology of Plants. The University of Chicago Press.

Pereira CG, Almenara DP, Winter CE, Fritsch PW, Lambers H and Oliveira RS (2012) Underground leaves of Philcoxia trap and digest nematodes. PNAS 109: 1154–1158.

Peterhansel C and Maurino VG (2011) Photorespiration redesigned. Plant Physiology 155: 49–55.

Raven JA and Edwards D (2001) Roots: evolutionary origins and biochemical significance. Journal of Experimental Botany 52: 381-401.

Zimmer C (2009) On the origin of sexual reproduction. Science 324: 1254-1256.