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In praise of plants, and the three-billion-year-old trap

When the light shone on the greenness, the greenness welcomed it, and comprehended it, and put it to use.” [Oliver Morton, Eating the sun]

The sunlight’s energy bounced from one molecule to the next like a frog across lily pads before reaching the subtle trap at the pool’s centre, the three-bilion-year-old trap where the light becomes the stuff of the earth.[Oliver Morton, Eating the Sun]

We need to talk about Kevin plants. I discovered this yesterday after having a revealing (and humorous) conversation with my lovely niece (5 years old; K) and nephew (3 years old; L), which went like this:

L: What are you doing today?

Me: Working.

L: What’s your work?

Me: Looking at plants.

K: Why don’t you do real work?

Me: …but this is real work. Plants are great.

K: But plants can’t do anything!

So I want to put the record straight! Plants are, in fact, the most fascinating creatures to study, and for any number of reasons: Plants power the planet, they have shaped Earth’s history and climate, they eat the sun, they produce most of the food we and other animals eat, they form the backdrop to the most beautiful views…the list is endless.

I am fortunate enough to be able to study plants for a living; one of the most rewarding career/life choices that I have made! Richard Feynman once wrote about the pleasure of findings things out…and I am constantly inspired by finding out new things about plants and how they function. I have been helped in this pursuit by many wonderful books, which I highly recommend. My top five books are: Eating the Sun (Oliver Morton), The Emerald Planet (David Beerling), The Secret Life of Trees (Colin Tudge), In Praise of Plants (Francis Halle), and The Wollemi Pine (James Woodford).

As a quick aside, the story of the Wollemi pine (not an actual pine, of course) is one worth recounting. Wollemia nobilis (which is closely related to the Auracaria‘s, or Monkey Puzzle trees!) is called a “living fossil” because it was first described from fossils, similar to the Coelocanth and the Dawn redwood. Living specimens of the plant were only discovered in 1994 (!) in a refugial valley in Australia’s blue mountains. Notice how similar the branches of the living plant are to the fossil specimens in the photo below, taken from The Wollemi Pine. Although the exact location of the natural populations is a well-kept secret, many plants have been grown in botanic gardens around the world since it was discovered. While I was in Australia I was lucky enough to see Wollemi Pines in the Royal Botanic Garden in Sydney in 2016 (see below) and in the Royal Botanical Gardens in Hobart.

So why are plants often under-appreciated? My theory, which is my own, is that us humans are biased towards focusing on things that stimulate or trigger our senses. We are hard-wired to pay attention to and appreciate movement and new noises, which is why birds and animals appeal to us. There is possibly an adaptive (or survival) element to this: animals and birds that grab our attention can be hunted and eaten. At the same time, we have also evolved to ignore less mobile and more common organisms or items because it would require too much energy to constantly focus on everything. The colour green is a good example: it is ubiquitous and constant during daylight hours. The three-billion-year-old chlorophyll trap works relentlessly while the sun shines to generate carbon-based products, and we would be hard pressed to acknowledge this incredible (microscopic) dance all the time.

The good news is that this under-appreciation can be over-turned. There are many ways in which the exciting world of plants can be brought to life. We can use our innate senses: Red excites us (because this is the color of ripe fruit…which is consistent with the survival aspect of interest that I mentioned in the previous paragraph), as do new smells from flowers. We can also observe plants in motion: seedlings growing towards the light, or the venus fly trap clamping down on a hapless fly. But more than that, we can learn new and exciting aspects about how plants work. Did you know, for example, that plants can have heart attacks?

Ode to oaks

One of the pleasures of comparative biology is exploring new places to find the organisms that are the focus of your research. During my postdoctoral research at the University of California, Berkeley I was fortunate to find myself in a position where I could explore the western part of North America in an attempt to better characterize the drought tolerance of temperate woody angiosperm trees. My study group was the wonderfully diverse oaks of North America. Nineteen species of oaks occur in the western part of the region (see Figure 1) and my goal was to figure out how they varied in capacity to withstand embolism (which I have written about previously).

Figure 1: Nineteen species of oaks (Quercus spp.) from western North America. A. Q. kelloggii (black oak); B. Q. agrifolia (live oak); C. Q. parvula; D. Q. wislizenii (interior live oak) E. Q. palmeri F. Q. chrysolepis (golden cup oak) G. Q. vacciniifolia H. Q. tomentella I. Q. sadleriana J. Q. gambelii K. Q. lobata (valley oak) L. Q. garryana M. Q. durata N. Q. berberidifolia (scrub oak) O. Q. pacifica P. Q. john-tuckeri Q. Q. douglasii (blue oak) R. Q. cornelius-mulleri S. Q. dumosa T. Notholithocarpus densiflorus (tan oak; not an actual oak, but a closely-related species)

As you would expect just by looking at the leaves of the different oaks, many of these species occur in vastly different habitats, including moist temperate rainforest (e.g. Quercus sadleriana; note the moisture on the leaves in the photo) and semi-arid desert scrub or chaparral (e.g. Q. berberidifolia) (see Figure 2). This meant that I had to sample species ranging from the pacific northwest close to the border between Oregon and California to the deserts of southern California close to San Diego.

The measurements that I was taking on each species involved drying the plants down from a hydrated state and visually capturing the point at which they fail (i.e. emoblise) using repeat photographs taken of the xylem. A key part of this measurement process is ensuring that the plants are hydrated when the measurements start. To ensure this I was required to collect the plants in the early hours of the morning, and then place them in a bag to prevent them from drying out. I also needed to take the measurements as quickly as possible from the time when I first collected the plants. The best way to ensure this was to make the hydraulics lab mobile! So, I packed up all the gear into my trusty steed (including scanners, pole pruners, pressure chambers, stem psychrometers and a whole bunch of other equipment) and hit the road (see Figure 3).

“I went to the desert on a horse with no name; it felt good to be out of the rain” [Americas]

On my travels I was accompanied by several incredible assistants, companions and collaborators. Together, we sampled oaks from all sorts of exotic locations. We sampled species in the high elevation deserts in southern California (note the snow), the pristine Channel Islands (we got there by ferry) and slow moving Los Angeles. It was very special to see exciting and diverse habitats and to meet many wonderful people along the way.

You will have to wait to see what we found…as that is a post for another day! One exciting initial finding though is the discovery that science moves at about the same pace as the traffic in Los Angeles (see Figure below)…

And the Andes!

My love affair with Chile continued today when I went on a field excursion to the Chilean Andes (Figure 1). I joined a group of delegates attending a conference on Hydrology on an outing to the San Pablo de Truega experimental watershed. The tour took us past some experimental stream gauges, designed to test the impact of forest thinning on stream flow. The site has two streams with monitoring gauges: a control stream in a relatively undisturbed natural forest stand and a treatment stream in a thinned forest stand. So far their results indicate that stream flow is vastly increased in the thinned site, primarily because fewer trees intercept rainwater and return less water to the atmosphere via transpiration, so more water ends up as run-off. Consequently results from this watershed are assisting foresters to manage the land, and also assist scientists in predicting future changes in water supply, an important ecosystem service.

DSC_8106

The highlight of the trip for me was definitely our hike to El Presidente – the largest Nothofagus tree in the forest (Figure 2). On the hike I saw magnificent Saxagothea, Nothofagus and Laureliopsis trees, and a Darwin Frog (Rhinoderma darwinii)! This unusual little creature relies on camouflage to avoid being detected by predators, resembling a fallen leaf (Figure 2). Another interesting aspect about the frog is that the male Darwin’s frog protects the eggs for about three to four weeks. After the female lays the eggs in the leaf litter the male guards them until the developing tadpoles begin to move, and then he ingests the eggs and retains them in his vocal sac! The baby frogs hatch about three days later after which the male frog continues to carry them in his vocal sac until they hop out and disperse. Remarkable.

After the hike we had a traditional Chilean barbecue. It was excellent, and I was absolutely stuffed with delicious steak, potato salad and blood sausage. Needless to say that most of the tour group slept on the bus on the way home.

I was pleased that the Andes lived up to (and exceeded) my expectations, both in terms of the diversity of plants, but also the beauty of the forests. These ecosystems really are magnificent, and I very much hope to return to them one day.

Journey to another distant world: Chile

Visiting South American temperate rainforests had always been on my wishlist, and recently I had the opportunity to go see some of these beautiful ecosystems in Chile. The opportunity arose when Rocio Urrutia, a researcher at the Universidad Austral de Chile in Valdivia, invited me to collaborate with her on a research project investigating the potential impacts of future climate change on temperate Chilean rainforest species (Figure 1). The focal species of the project is Alerce (Fitzroya cuppresoides), a conifer species often referred to as the “redwood of the south”. This magnificent tree is threatened by drought events, habitat destruction, and illegal logging, and Rocio and her colleagues are doing some fantastic work with the aim of promoting conservation of the trees and the forests that they occur in.

Upon my arrival in Validivia, I was immediately struck by the trees; Many of them seemed oddly familiar. On the way to the city from the airport my taxi drove past Chilean firetrees in full bloom (Embothrium coccineum, members of the Proteaceae), and magnificent southern beech trees (several Nothofagus species). I am particularly fond of species of the Proteaceae, mostly as a result of having grown up in South Africa where Protea, Leucospermum and Leucadendron are common features of the Fynbos flora (and also as a consequence of having studied the Fynbos flora for my dissertation).

One of the reasons for my trip to Chile was to participate in a discussion around the conservation of Alerce (Fitzroya cuppresoides). The mini conference was excellent (Figure 2). Among other things, I learned that even though the mean annual rainfall of Alerce Costera is over 4000 mm, Alerce trees can experience water stress during dry years as a consequence of the shallow, sandy soils. I was also highly impressed to learn that Fitzroya is the second longest living tree in the world (and I met the individual who dated the tree – the wonderful Antonio Lara!). I found this remarkable because these trees are quite different in appearance from the longest living trees in the world, the Bristlecone Pines. Alerce is tall, and flourishes in its native habit (moist temperate rainforest); in stark contrast the Bristlecone Pines appear to persevere rather than grow in arid mountains of North America. It really is unfortunate that these Alerce forests are threatened by climate change and deforestation. Overall the conference was incredible. It was fantastic to learn about the ongoing research at the University.

Screenshot 2018-11-03 10.34.09

After the formalities of the conference were completed, my wonderful hosts, Rocio and Aldo took me and a few other colleagues (Jarmilla Pittermann and Jonathan Barichivich) on a field excursion to see the Alerce Costero forest (Figure 3). The forest is a two-hour drive from Valdivia and the site of much long-term monitoring and experimental research conducted by Rocio, Jonathan and their colleagues.

When we arrived I was awestruck to be standing amongst Nothofagus, Fitzroya, Pilgerodendron and Saxagothea. Incredible. My mind wandered to the last time I was standing in a mixed Nothofagus-conifer temperate forest. That time, I was travelling in New Zealand, but the similarities between the two forests are striking. Of course, the similarity between the southern hemisphere flora is no coincidence. The splitting of the ancient continent of Gondwana resulted in many shared families between the countries, including the Proteaceae, Myrtaceae, and Podocarpaceae. Antarctica was also a part of this supercontinent, as demonstrated by the abundance of fossils of tree species that occur on the cold continent. Remarkably, some of the fossil species still exist in the Alerce Costero temperate rainforest; I was amazed to see Nothofagus antarctica trees for the first time, surviving in a small drainage basin frequently exposed to very cold conditions (Figure 4). Its occurrence on Hoste Island (one of the southernmost islands in Chile) earns Nothofagus antarctica the wonderful distinction of being the southernmost tree on earth! Tangible, living evidence of these ancient geographic links between the southern hemisphere land masses.

After our walk through the forest and the research sites we retired to a small cafe located on the outskirts of the Alerce Costero National Park. Jonathan’s mother runs a tiny cafe where she provides warm refreshment in the form of coffee and baked goods (Figure 5). It was delightful. We crowded into the cozy, warm room and had an incredible lunch.

Finally, we decided to see the big Grandpa of the forest: the largest Alerce of the region (Figure 6). This tree is one of the few remaining large trees of the forest, with most of the large trees having been cut down in previous centuries for timber. It is incredible! It has a known diameter of at least 4m and is at least 2000 years old according to tree rings obtained by Antonio Lara (It is probably much older, since the inner core has rotted away with time).  Jonathan mentioned that the sex of the tree is actually unknown (Fitzroya is dioecious, meaning that, like humans, individuals can have seperate sexes). However, they aim to find this information out later this year….and Jonathan suspects that the tree is actually the Grandma of the forest.

So far my experience of Chile has been wonderful, and I still have a week to go here. It is great to be among southern hemisphere trees again and to learn about more remarkable southern hemisphere forests!

Low vulnerability to xylem embolism in leaves and stems of North American oaks

Have you ever wondered how plants become damaged and die during drought? As a post-doctoral researcher investigating plant physiological responses to water deficit, I spend most of my time thinking about this question. A very smart young lady once told me that it’s obvious…they run out of water. In one sense, she is absolutely correct: when the leaf mesophyll cells run out of water (desiccate), they become unable to maintain normal physiological function, which ultimately leads to death. But this explanation is not entirely satisfactory: It does not tell us about the precise processes that lead to desiccation, whether there is a particular threshold of desiccation that plants fail to recover from, and how different species might vary in their capacity to withstand desiccation. I have been investigating these questions in Californian oaks, and recently published my findings in the scientific journal Plant Physiology.

To find a satisfactory answer to the question, we need to revise some fundamentals about how plants function. Not having a heart, or a mechanism to pump water to the tops of their canopies, trees rely on gradients in water concentrations. Water naturally and passively moves from places of high concentration to areas of low concentration. As water is drawn out of the pores on leaves (stomata), it is replaced by water from the rest of the plant. Plants replace this water lost to the dry atmosphere by taking up moisture from the soil. Within the plant water is transported in xylem: from the roots, all the way to the leaf mesophyll cells. Think of this process as similar to an elastic band being stretched from the tops of the canopies. As the environment dries, plants find it harder and harder to extract moisture from the soil. The elastic band stretches…

Xylem embolism

We currently think that as the tension in the water column increases, air is eventually drawn into the xylem vessels and the elastic band snaps. This process creates an air pocket that blocks the transport of water, know as embolism. Xylem embolism represents a significant, drought-induced damaging process in land plants. As plants embolise they lose the capacity to hydrate the downstream cells in the leaves. So this partly answers our question: the point at which plants experience embolism is the point at which they begin to suffer (mostly irreversible) damage.

However, substantial debate surrounds the capacity of species with long xylem vessels to resist embolism. Some studies have shown that species are highly vulnerable to embolism, and regularly experience this during dry periods, while others suggest that plants are actually less vulnerable to embolism. Our paper investigated whether recent methodological developments could help resolve this controversy within oaks, a  charismatic, ecologically important, temperate angiosperm genus. We were hoping to shed further light on the importance of xylem vulnerability to embolism as an indicator of drought tolerance in long-vesselled trees. To do so we used a non-invasive optical technique to visualise embolism in leaves and stems of eight oak species from the Mediterranean-type climate region of California, USA. Basically we took a lot of photos of trees as they dried down and monitored when they embolised.

We show that the point at which air enters into leaves ranges from −1.70 MPa to −3.74 MPa, and from −1.17 MPa to −4.91 MPa in stems (pure water is 0 MPa and plants normally operate above -1.5 MPa). Consequently, our results show that long-vesselled North American oak species are more resistant to embolism than previously thought, and support the hypothesis that avoiding stem embolism is a critical component of drought tolerance in woody trees. So now we can say exactly when particular oak species start to fail during drought.

This information is useful, as it allows us to predict how oaks might respond to future drought events. It tells exactly when they will start to lose function, and become damaged. In fact, our study shows that accurately quantifying xylem vulnerability to embolism is essential for understanding species distributions along aridity gradients and predicting plant mortality during drought. All we need to do is monitor their water status to know whether they will recover or not. Ultimately, this is why physiological studies, such as ours, are important: They allow us to be precise in understanding how plants respond to climate change.

How plants respond to drought provides insights into climate change survival

Globally, droughts have had a negative impact on many plant species. This has led to much higher rates of mortality than usual. Understanding how different species are likely to respond to drought is crucial to accurately predicting the impact of future climate change on plant communities.

Plants in South Africa’s Western Cape area have tremendous variation in their sensitivity to drought. Photo: A. Betzelberger.
Plants in South Africa’s Western Cape area have tremendous variation in their sensitivity to drought. Photo: A. Betzelberger.

It can be extremely challenging to find meaningful ways to describe plants’ many different types of responses to drought, particularly in biodiverse areas. Scientists have been working to develop a new system in which plant functional traits can be used to assess the range of drought tolerance in diverse plant communities.

Why some plants shrivel and die and others don’t
Although it may be tempting to think that drought is bad for all plant species, there is tremendous variation in their sensitivity to drought. For several decades, plant scientists have been attempting to figure out what determines this variation. But there are no simple universal measurements of drought tolerance. Instead, scientists usually rely on long-term experimental manipulations.

The difficulty of assessing drought tolerance makes it challenging to work with large numbers of species. It is critically important that we do so, particularly within the world’s biodiversity hotspots – they are incredibly important systems for the planet. They include the tropical rainforests – the lungs of the planet – and many economically significant ecosystems such as South Africa’s fynbos.

Trade-off between water loss and carbon uptake
A recent paper offers a solution to the challenge. It proposes using simple plant characteristics or traits to identify the different strategies that species adopt to cope with drought. The beauty of using plant traits is that they are relatively easy to measure, and can be gathered for a large number of species. The system uses combinations of easily measured plant traits to get an index for drought tolerance in much the same way as body mass index works in humans. You can measure relatively simple traits like weight and height and combine these to determine how a person might react to stress or exercise.

To predict how different plant species respond to drought the researchers focused their trait selection on the classic water-loss versus carbon-uptake trade-off that plants face. When land plants open their stomata to allow carbon dioxide to enter the leaf for photosynthesis, they inevitably lose water. This creates a carbon-uptake-water loss trade-off, particularly under water limiting conditions. During periods of drought plants face a dilemma – to continue to photosynthesise and risk desiccation or close the stomata to conserve water but risk starvation.

Studies were conducted to determine how plants like the Protea adapted to drought. Photo: A. West.
Studies were conducted to determine how plants like the Protea adapted to drought. Photo: A. West.

Tracking two plant traits
The scientists recognised that two plant traits would be critical to determine which side of the trade-off different species tended to err towards. The first trait relates to how a plants’ internal plumbing responds to dehydration: the ability of the xylem to withstand desiccation. Water is transported from the soil through the stem to the leaves under tension, which gets greater under drought stress. When the plants become too dehydrated the water column breaks and air enters the stem, which blocks the vessel. This is similar in some sense to an embolism in human arteries and is potentially as fatal for a plant as it prevents them from moving sugars to where they are needed.

The second trait relates to the breathing apparatus, or stomatal response of a plant. Stomata operate like variable resistors on the leaf surface, opening and closing in response to desiccation. The sensitivity of the stomata varies between species. In some species they may be highly responsive to changes in water status and less so in others.

Scientists have known for a while that both xylem vulnerability and stomatal response varies between species. But the association between these traits and the ability of a species to survive droughts remained unclear. The key missing element was how the xylem and stomatal responses are co-ordinated within a species. Very few studies have addressed co-ordination between stomatal regulation and xylem vulnerability and then used this to predict how likely a species is to die during drought.

Lessons offered up by Fynbos
To test the system, the authors studied fynbos communities in South Africa’s Western Cape. These highly species-rich plant communities are recognised as one of the world’s biodiversity hotspots and contain three major plant functional types: the familiar proteas, restios and ericas.

Restios are highly diverse in fynbos, which makes these communities more resilient to change. Photo: R. Skelton
Restios are highly diverse in fynbos, which makes these communities more resilient to change. Photo: R. Skelton

Different species adopted a continuum of strategies. It ranged from a risky, low safety-margin response to a more conservative approach to water loss. A key finding was that species which were more conservative and closed their stomata earlier in response to desiccation were less likely to incur xylem embolism. On the other hand, species that closed their stomata later were more likely to incur xylem embolism.

It was also possible to make predictions about how different species might die during drought. Worryingly, the study suggests that many restios and ericas appear to be particularly sensitive to drought. This may lead to shifts in the future composition of fynbos communities.

On a more positive note, the study also showed that all three familiar fynbos plant types had representative species from the full range of responses. This suggests we are less likely to see any one plant type disappear. It highlights the importance of biodiversity for landscape resilience. Having species of each functional type respond differently to drought may allow a community to be more resilient in the face of change

This article was originally published on The Conversation. Read the original article here:

https://theconversation.com/how-plants-respond-to-drought-provides-insights-into-climate-change-survival-44017

Also, the PNAS paper can be downloaded here:

http://www.pnas.org/content/112/18/5744.abstract

Thoroughly modern conifers?

Who could compete with the angiosperms?

“The redwoods, once seen, leave a mark or create a vision that stays with you always. No one has ever successfully painted or photographed a redwood tree. The feeling they produce is not transferable. From them comes silence and awe. It’s not only their unbelievable stature, nor the color which seems to shift and vary under your eyes, no, they are not like any trees we know, they are ambassadors from another time.” John Steinbeck from Travels with Charley in search of America

Some of the most impressive trees on earth are conifers: a redwood (Sequoia sempervirens) is the tallest tree in the world and a bristlecone pine (Pinus longaeva) is the oldest. Yet, redwoods (plants of the subfamily Sequoioideae) and several other conifers are often considered to be relics, primitive survivors from a distant era (Figure 1). Many would agree with Steinbeck’s sentiment that conifers are ambassadors from another time.

Indeed, the three extant genera known colloquially as the “redwoods” – Sequoia, Sequioadendron and Metasequoia – are all that remain of a once-much larger, ancient sub-family: the Sequoioideae. The fossil record shows that the Sequoioideae were widespread in the Cretaceous (about 140 to 70 million years ago), being particularly dominant in northern latitudes. However, the reign of the redwoods began to draw to a close in the late Eocene and continued throughout the Oligocene, when both the range and diversity of Sequoioideae declined. Today only three species cling on in refugial areas in China and California, and all of them are highly threatened by climate change and habitat destruction.

The demise of the redwoods is captured well by the fortunes of the genus Metasequoia. The genus has a very extensive fossil record and was one of the most common taxa in the Cretaceous and Paleocene in the Northern Hemisphere. At least three distinctive fossil species have been described from this era (although there may have been as many as twenty according to some authors). And as if to further emphasize the point that Metasequoia is a remnant genus, the only extant species – Metasequoia glyptostroboides – was first described from fossil material in 1941 and, following the later discovery of living plants in China in 1948, is commonly regarded as a living fossil.

Mirroring the story of the northern hemisphere giants is that of the once-great southern hemisphere conifer family, the Araucariaceae (Figure 2). In the Cretaceous the araucarians were widespread in the southern hemisphere (and even extended into the northern hemisphere). Today, most species are found in moist rainforest refugia in New Caledonia and Papua New Guinea. The number of genera has fallen from approximately six during the Cretaceous to three that are extant. One of the extant genera (Wollemia) contains only a single species (Figure 3). Similar to the story of Metasequoia, Wollemia nobilis was first described from fossils and was only discovered in a refugial valley in Australia in 1994. Another living fossil!

The two most likely reasons for the decline of these noble plant families were climate change and the rise of the angiosperms. Global cooling in the Eocene and Oligocene appear to have had a major impact on conifer diversity and abundance. Aridification and the evolution of fire-adapted flora in many parts of the world may also have contributed to their decline. The flowering plants (angiosperms) also evolved 120 million years ago and have since expanded to fill many of the niches previously occupied by gymnosperms. Angiosperms have been suggested to be more competitive, faster growing and better adapted to fire than conifers. Indeed the angiosperms are truly an incredible group, accounting for over 80% of the roughly 297 000 species of known land plants (Figure 4). In comparison gymnosperms account for less than 0.5%. Angiosperms are the dominant plant forms in the tropics and subtropics: most of the species in the rainforests tend to be angiosperms. Modern broadleaved tree species are the lungs of our planet. If humans had to choose five families to coexist with into the future, we would almost certainly choose the grasses (Poaceae), daisies (Asteraceae), orchids (Orchidaceae), madders (Rubiaceae) and legumes (Fabaceae). Together these five families contain approximately a third of all plant species and contain the most ecologically and economically important species. So for all the splendour and nobility of the gymnosperms, the angiosperms are indispensable.

So it seems as though the Sequoioideae and the Araucariaceae have had their heyday, along with the dinosaurs that once browsed on their foliage. Yet, just as with the dinosaurs, perhaps it is time to reconsider whether this idea pertains to all conifers. The Pinaceae and the Cupressaceae appear to have radiated fairly recently and occupy vast tracts of land, particularly in the boreal zones of the northern hemisphere. Pines (actual pines…and not “pines” from the southern hemisphere) are tremendously important economically. Junipers are both diverse and widespread. Yet, despite their areal dominance, the pines and junipers still tend to be restricted to more marginal growing areas: northern latitudes and deserts or semi-deserts. Species of these families found in the tropics tend to occupy mountain slopes or moist refugia. Few can compete with modern broadleaved species in the tropics.

Only one conifer group that I know of seems to have taken on the angiosperms at their own game in the tropics and done surprisingly well. Surprisingly, the Podocarpaceae have diversified in recent times in the tropics. The reason behind this is linked to their leaf shape. More basal podocarps, such as Lagarostrobos franklinii or Microcachrys tetragona, cling on (just as the redwoods do) in refugial habitats. These more basal species tend to have scale-like leaves and slow growth rates. Yet, a group of species within the Podocarpaceae have developed broader, flattened leaves or phyllodes and more efficient conducting networks in their leaves (Figure 5). These innovations allow them to have relatively high growth rates, which in turn allows them to compete with angiosperms. Evolution never fails to innovate.

Apart from being a natural tale about the underdog triumphing against the odds, this story also provides some deeper insight into how evolution proceeds. It shows how inadequate it is to label species as either “modern” or “ancient”. Instead, it is more accurate to think that all extant lineages are good enough. Conifers, like the dinosaurs, were once the dominant plants on land. As always, whether a lineage persists through time is partly based on luck and partly on innovation. Although many conifer lineages succumbed to the voracity of time others have subsequently persisted and, like many podocarps, have even radiated. Like the birds, these extant lineages are thoroughly modern: they survive and compete successfully with other modern taxa. It is erroneous to think of birds and podocarps as remnant species. Instead, the next time you find yourself ogling over a yellowwood consider how thoroughly modern it is.