Tatooine’s tangled bank – plants evolve in a galaxy far, far away
“It is interesting to contemplate a tangled dune, clothed with many plants of many kinds, all produced by laws acting around us. There is grandeur in this view of life, where so unforgiving an environment has taken but one common ancestor, and, over the millennia, forged such marvellous forms most beautiful. That this should occur, as it does elsewhere, in such an inhospitable place, speaks to the power and the universality of evolution – a creative force that that exceeds the Force in its impact in our galaxy.” from The Origin of Tatooine Species, by Momaw Nadon (50 BBY – 50 ABY)
There is nothing like a voyage to a distant land to reinforce the incredible diversification of nature.
I undertook such a voyage some four years ago. I now find myself in a place so distant from that which I considered “normal”, in both location and character, that the mere existence of life is testimony not only to its capacity to diversify, but to survive at all. So harsh is the environment here that it beggars belief that anything can cling to life in this place, let alone flourish.
But I am getting ahead of myself.
Let me step back in time to introduce you, as I was, to this distant land.
My first footsteps onto this place were disorienting. After what had seemed an impossibly long time aboard the ship, the solidity of terra firma felt peculiar somehow. As it is, gravity aboard ships always seems to operate in unusual ways, and I am more susceptible to ship sickness than most. Stepping off the finished surface of the ship’s docking plank, onto the rocky land, was simultaneously strange and comforting – strange after having grown accustomed to the ship’s movement; comforting to be standing on solid ground again. And then the intensity of our destination struck me squarely.
The heat was forceful. We had docked the ship not long after sunsrise, and the temperature was already hovering near 40 degrees. By double noon, an additional 10 degrees could be counted on.
It was a dehydrating heat. The humidity of the air here is said to average 5.4%, with little variance about that value. In my homeland, humidity can reach 100%, as gentle showers nourish the land beneath.
Such a stark contrast with our destination.
After the humid confines of my quarters aboard the ship, the daytime heat of the place felt oven-like – it seemed to suck the moisture right from your skin, eager to roast you alive. Yet, during the night, after sunssets, the temperature would plummet. With no humidity to hold the warmth, the nights could be unbearably cold. The daily cycle of blistering heat and bone-numbing chill lent a degree of meanness to the place.
A survey of the nearby land bore testimony to the brutality of the daytime heat, and the frigidity of the night. The surface appeared scorched. Sandy dunes, peppered with hard-baked rocky outcroppings, created a landscape that was simultaneously serenely sculpted yet harshly foreboding. It was a landscape to look at, but not one that welcomed you. Yet my exile to this place meant that I must welcome it, even if it did not welcome me.
I knew the land would be this way. It had been made this way not yet 26 millennia ago. Its history was well known. Its history could be read in the rocks and the sands, and heard in the lore of its indigenes.
This arid land once sat beneath a beautiful, if tumultuous, ocean. The ocean was bordered by lands with lush forests and coastal plains. But the seas had been boiled away, and this severe land took its place – rich in silica and basalt – to create the desert to which the ship had brought me.
At first glance, it seemed impossible that anything could make its natural home here. With passing time, I learned that nothing could be further from the truth. A surprising abundance of life had taken a foothold here. Within a mere 25000 years, this most inhospitable of places now played host to remarkable plant and animal life.
Much has been made of the spectacular beasts that reside in this arid place. Their fearsomeness speaks to the hostile environment in which they thrive. Dramatic though they are, the existence of these creatures is not the one that gives me cause to marvel. A creature can retreat from the midday suns to the shelter of shady cliffs and caves, or burrow beneath the sands to escape the midday heat. A creature can huddle amongst its own kind, in herds or colonies, to contend with the chill of the night. A creature can actively search out sources of water, track down prey, find a mate.
Creatures can accomplish all of these things by movement and behaviour. Such traits may inspire awe and wonder, but they are nothing in comparison to what must be done by organisms that are literally rooted in one place – plants. That is, the challenge of this ruthless environment is most felt by those that cannot run nor hide nor huddle nor search. Plants must find a way to face the harsh conditions face on, harvesting the light from the suns without suffering its mean effects, and gathering water from a place where it is scarce.
Yet even here, in this mean place, plants not only survive, they thrive. Non-native plants can flourish, but this requires the helping hand of the gardener. I have grown plants from my homeland here – with trees standing 10 meters tall and with girths of 50 cm, in a mere 3 years. But this required irrigation, shading, fertilising. I merely approximated the conditions of their homeland, and was abetted by the continuous growing season of this land. If left to their own devices, my fellow expatriates would perish – succumbing to the excessive heat of the day, and the absence of accessible water.
The native plants here have no such problems contending with these conditions.
By far the most important plant of this region, the hubba gourd’s melon-like fruit supports a diversity of animal life. This includes the indigenes, who value it as their primary food source – eating its thick-skinned fruit after roasting, or extracting its sour juice for liquid refreshment. So important is this plant that the word “hubba” means “staff of life” in indigene language.
The hubba plant has starchy, segmented stems that can snap off into finger-length portions. These segments roll very efficiently along sand or rock when propelled by the wind. When they roll into an area that has shade, these segments proliferate hair-like projections along the length of the segment. Some of these projections embed themselves deep within the sand or rock, while others remain exposed to the air. Close examination of these hairs reveals that they contain complex carbohydrates and proteins that are hygroscopic – they take up water. As such, the hairs function as water wicks, extracting any moisture that is found in the air, sand or rock.
Once secured in place, and collecting water, the hubba stem segments produce a small flower. The flower has long extending anthers that release pollen to the wind. Hubba pollen can blow tens of kilometres in the open desert. Once this pollen fertilises a different flower, the hubba fruit – the gourd – develops. The gourd itself is green and photosynthetic, it can capture light and convert it to sugars. The hubba fruit is protected from the sunslight, by incorporating silica from the sand into its hard shell, where it reflects much of the midday light, but still allows enough to be transmitted through the skin to be used for photosynthesis. The fruit’s thick skin also prevents water loss, so that moisture is retained within the fibrous body of the melon.
The hubba plant can best be described as a shade lover and a reflector. It avoids the damaging effects of sunlight by growing only in the shade, and by creating a reflective coating. This strategy is in striking contrast to the molo shrub.
While the molo shrub also prefers to grow in the shade, it can grow in the full light of the day as well. During the day the molo shrub is not green, nor does it appear as anything more than a bunch of segmented, woody stems. During the night, however, the molo shrub erupts into a seemingly different kind of plant altogether.
The daytime, segmented “stems” of the molo shrub actually comprise tightly furled leaves. In the night-time, after the sunssets, the “stems” unfurl, such that they are now coated with beautiful slender leaves, and, depending on the time of the year, flowers. Waving in the cool evening breezes these leaves capture moons’ light. The deeply green, almost black, leaves contain a photosynthetic pigment that captures almost all available light. They are perfectly suited to capturing the suns’ light reflected in the moons.
Like the hubba, the molo also has fine, hair-like appendages that contain the same suite of hygroscopic, water-sponging, carbohydrates and proteins to capture water from the air and from the ground. Also like the hubba, the molo flowers are wind-pollinated, but their flowering time is offset from that of the hubba, occurring only during the annual foggy season.
Both the hubba and the molo live in the open. Their life strategies depend on light collecting organs that capture light at different times of the day. The funnel plant employs a yet another, different strategy.
The funnel plant embeds itself deep within rocky crevices, or, failing that, in seams in sandy aggregates. Here it creates a J-shaped, funnel-like organ that gives the plant its name. The organ is actually a set of highly elaborated, overlapping leaves, each emerging from different segments along the length of a segmented stem – not unlike the unfurled molo. Together they form the funnel shape. On the inside of the funnel, the same hair-like appendages emerge from the stem. Together, the funnel and the hairs resemble the interior of a hairy human ear. But together, they also function as a highly efficient condenser – capturing water from the air, both within the hairs, and in the bottom of the J, where the air is cooler, and trapped moisture collects on the hygroscopic interior of the leafy funnel. Photosynthesis occurs in the leaves that are at the lip of the funnel – in a thin band that sits on the top of where the funnel emerges from its underground refuge.
Like the hubba, the funnel plant produces one flower, but it only does so every two years or more. Again, it is wind pollinated, but it has much heavier pollen that rolls along the ground, so that eventually it tumbles into a receptive funnel. In keeping with this, the pollen-releasing anthers rise up out of the funnel; whereas, the pollen-receptive stigma lies deep within the funnel.
When I arrived in this land, I was struck by the diversity of strategies employed by the plant life to contend with the conditions here. The hubba and the molo, above-ground dwellers both, prefer the day and the night respectively. The funnel plant, on the other hand, escapes the conditions by burying itself. Three entirely different approaches to contend with precisely the same conditions. But I was also struck by the similarities: the reliance on wind pollination; the use of hair-like appendages; and the employment of hygroscopic macromolecules to collect water.
What was I to make of these similarities?
Such similarities undoubtedly reflected some sort of shared ancestry. This would not be surprising. The land here was exposed to a thorough scorching, through which only a handful of plant species could be imagined to survive. Perhaps only a small handful of plants founded the diversity of plants now found here. This was a hypothesis worth testing.
The test proved surprisingly easy. All of the plants were wind pollinated, but none flowered at a time where they could cross-pollinate each other. What if I was to foil this separation of pollination? What if I took pollen from each of the plants, and cross-pollinated them by hand?
The experiment was straightforward. I collected pollen from each of the plants – from the hubba, the molo, and the funnel. I then applied it to the stigma of a member of its own species to ensure it was functional. In each instance, fruit formed shortly after the pollination – the gourd of the hubba, and smaller, multiseed fruits for the molo and funnel plant. I then cross-pollinated each of the species with each other – reciprocating each kind of pollination. Hubba pollen on molo stigmas. Molo pollen on hubba stigmas. And so on.
To my delight, all produced fruit. What’s more, the fruit produced seeds that germinated and gave rise to plants that were precisely intermediate between each parent. Imagine! A funnel that curled its leaves up every day. A hubba that burrowed its stems into the soil. Remarkable.
Also remarkably, each hybrid was poorly suited for the environment of that land. A buried hubba cannot produce a fruit that can photosynthesise. A curled leaf funnel cannot collect water. In short, had I not practiced good gardening with them, the hybrids might all have perished. Instead, I saw them all through to flowering. Then I crossed hybrids with hybrids.
What emerged from this second generation was equally remarkable. The traits began to sort themselves out. Some plants were more like one grandparent than another. If I let the environment select which it favoured, it is easy to imagine that, within relatively short order, I would recover the original species types again.
Together my simple breeding experiments suggest that the plants shared a common ancestry that, over time, had diversified to produce the species now present there today. The process that we call evolution in my homeland was clearly at play in this place also. This is not so surprising, although the timeframe in which this occurred was impressive.
How had such diversity emerged in a mere 25000 years? Perhaps the makings of this diversity already resided within the plant life that preceded the arid conditions. Alternatively, perhaps the sunslight in this place hastens the pace of emergence of variants upon which selection could act. Further experiments, or indeed, querying the indigenes about their knowledge of the plants, pre- and post-aridity, might provide some insights into these hypotheses. Either way, in a short period of time, evolution had created plant life that thrived under conditions that would make even the most resilient of beings from other places wither.
I find solace in the resilience of the hubba, of the molo, of the funnel plant. I like that they have different ways of accomplishing survival under the same adverse conditions. And there is something comforting in the fact that evolution “discovered” these diverse strategies using the same starting materials – a primordial ancestor that enjoyed a very different, arguably easier, life. It gives me hope that my exile to this distant land, to this distant planet, so very different from my home world, will not wither me. Instead, I hope that my exile will provide me with different ways of thinking – new strategies to make my way through this life – so that I may not just survive, but thrive, in this time of turmoil, in this time of tumultuous change.
May that a creature like me, product of the beautiful planet Ithor, with its forests, jungles, rivers and waterfalls, be forged into a better being by the dry winds and demanding environs of Tatooine. May this planet shape me like it has shaped the resilience of its botanical denizens.
Posted on behalf of Momaw Nadon, Tatooine, 0 ABY
Note from MMC: This post is obviously a huge departure from what I would normally write here. That said, the post was a lot of fun to write, and I hope that you enjoyed it. It is part of the Science of Tatooine Blog Carnival organised by the fantastic Matt Shipman. If you would like to read more about the Science of Tatooine, please make sure to check out the following posts in the blog carnival: