Walking Palms

I don't know about you but Socratea exorrhiza has to be the strangest species of palm that I have ever laid eyes on. Native to Central and South America, its peculiarly stilted appearance has earned it the common name of "the walking palm." Whereas most palms invest in heavy trunks, the walking palm sends out a lanky set of stilt-roots upon which the palm grows like some otherworldly tripod.

There has been a lot of debate over the last few decades as to the purpose of these stilt-roots. In 1961 it was suggested that they were an adaptation for living in swampy areas. To date, no evidence of this has been found. Others have suggested that these roots are relatively cheap to produce compared to a solid trunk, thus allowing more investment in growing taller in a shorter amount of time while still maintaining structural integrity. This sounds attractive and is probably part of the puzzle. However, I feel that a particular study published in 1980 offers the best explanation.

Tropical forests are full of decomposition. The omnipresent threat of rot means there is a constant rain of limbs and snags from the canopy above. Trees regularly topple as well. For most plants, getting flattened by such debris is usually fatal. This is not necessarily so for the walking palm.

It has been observed that walking palms flattened by a fallen limb or tree can actually "walk" themselves out from underneath. Since most of the trunk is capable of producing stilt-roots, it doesn't take long for a new anchor to become established. Once this occurs, the palm is free to continue its journey into the canopy.

Getting squashed isn't the only worry either. Light is a premium in the deep shade of a rainforest understory. It is also short lived. A hole in the canopy that provided ample light one week may quickly close in the next, removing the life-giving rays of the sun. If a plant were able to "move around" it could potentially relocate to a sunnier spot. In a sense, this is what the walking palm does.

Walking palms are positively phototropic, meaning they lean towards a light source. Leaning can put stress on a trunk to the point that the tree topples over. The walking palm gets around this by sending down those stilt-roots, which provide support as it chases light through the canopy. In a sense, this palm "walks" itself around the forest in search of the best light. Whereas most trees are stuck where they germinate, the walking palm has, in a sense, freed itself from such restrictions. As such, older trees are often found far from their original germination point.

Once in a favorable location, the walking palm will right itself and continue upwards. At this point, the old trunk and roots are superfluous and will often rot away. For a young tree, this process can happen in as fast as two or three years. This is an incredible feat considering the time scale most trees operate on. Personally I would love to be able to observe a forest with walking palms over a few decades. Seeing how their positions change with time would be fascinating. At the very least, their bark is often covered in epiphytes, which offers a lot to comb over on our timescale.

Photo Credits: Hans Hillewaert (Wikimedia Commons) and John H. Bodley and Foley C. Benson (infographic)

Further Reading:

http://www.revistas.ucr.ac.cr/index.php/rbt/article/view/5955

http://www.jstor.org/stable/2387775?seq=1#page_scan_tab_contents

The Largest Seed in the World

Coco_de_mer.jpg

For Lodoicea maldivica, better known as coco de mer, producing the largest seeds in the world may seem like a cool fact for the record books but it certainly has its drawbacks. However, as with anything in nature, selection would not allow for wasteful traits to be passed on. Costs must be offset by a reproductive advantage on some level. A recent study looked at what these tradeoffs might be for L. maldivica and what they found is pretty incredible.

With seeds clocking in at upwards of 30 kg (66 lbs.) one has to wonder what L. maldivica is up to. It was long thought that, like the coconut, seeds of this palm must be dispersed by water. However, they are simply too dense to float. Instead, seed dispersal for this peculiar species of palm is actually quite limited. They simply fall from the tree and germinate below the canopy.

This may explain why L. maldivica is endemic only to the islands of Praslin and Curieuse in the Seychelles. It's not just the seeds that are huge either. The female flowers, which are borne on separate trees than the males, are the largest female flowers of any species of palm. At 10 m (32 ft.) in diameter, the leaves are also massive, fanning outwards on petioles that can reach 2 m to 4 m (6.5 - 13 ft) in length. It goes without saying that L. maldivica is a palm full of superlatives.

Counterintuitively, the habitats in which they grow are notoriously low in nutrients. Why then would this palm invest so much energy into growing these gigantic structures? Because they tend to germinate and grow beneath their parents, the offspring of L. maldivica would appear to be at a disadvantage from the start. A recent study suggests that the answer lies in those massive leaves.

Researchers found that the areas directly beneath the adult trees were wetter and had more soil nutrients compared to the surroundings. As it turns out, L. maldivica modifies its own habitat. Those massive leaves do more than just collect sun, they also act as giant funnels. In fact, most of the water that rains down onto the canopy is collected by the leaves. In this way, everything from water, debris, and even excess pollen is funneled down to the base of each tree.

Not only is this good for the parent tree, it is also a boon for the dispersal-limited offspring. Coupled with the considerable endosperm in those massive seeds, all of this additional water and fertilizer means that seedling L. maldivica enter into the world at a distinct advantage over many other plants on the islands. All of that endosperm serves to help fuel seedling growth while it is still shaded by its parent.

Sadly, over-harvesting of the seeds has crippled natural reproduction for L. maldivica. This coupled with habitat destruction paints a bleak picture for this record-holding palm. It has already been lost from three other Seychelles islands. Luckily there are many conservation efforts underway that are aimed at saving L. maldivica. The Seychelles are now considered a World Heritage Site and many of the wild populations of this palm lie within national parks.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]