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Those of you who have been listening to the new podcast will know that Andy came up with an idea for an Anemone Tree. The idea is that this "tree" would prey on small animals for some of its needed nutrients.

In a vein similar to the Anatomically Correct Series we would like some help making this thing work in a realistic way. It need not be biologically a tree it can be an animal (anemones are animals) but should still resemble a tree as closely as possible.

The "tree" should have the following characteristics:

  • The branches should have some way to react to prey not dissimilar to the whomping willow (for those familiar with Harry Potter). The branches would not need to be fast, just able to move.
  • Some mechanism in the branches/leaves should disable prey, it can kill, stun, paralyze...take your pick.
  • The tree needs to, in some way, consume the prey it disables. Letting corpses decay all around it so they can be absorbed like a normal tree is out, the tree needs to eat them, think Venus Fly Trap.
  • The tree should have a woody bark-like trunk, design wise we would like the trunk to look similar to a swamp cypress.
  • It should pass as an actual tree upon cursory inspection. If I am walking through the forest I wouldn't notice it until I was close or specifically looking for one. The forest in question is quite dense.
  • The tree should grow larger over time like a real tree. If it needs to cap out in size for some reason it should grow at least 25' (7.6m) tall.

Best answers will allow for all of the above while maintaining as much a tree like appearance as possible.

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    $\begingroup$ Have you taken a look at the existing list of carnivorous plants? You might find some ideas there. $\endgroup$ – Draco18s Dec 21 '17 at 17:48
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    $\begingroup$ Most of questions in anatomically correct series has "anatomically correct" in title, right? Consider adding it. $\endgroup$ – Mołot Dec 21 '17 at 18:01
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    $\begingroup$ How do you get 4 good answers in a couple hours? I need to learn how to ask better questions. $\endgroup$ – kingledion Dec 21 '17 at 20:55
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    $\begingroup$ @kingledion 3+ years of practice :D $\endgroup$ – James Dec 21 '17 at 21:20
  • $\begingroup$ @kingledion Three plus years, indeed! That's what I call an unfair advantage $\endgroup$ – a4android Dec 22 '17 at 4:40
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The Common Swamp Anemone

Like its cousin the sea anemone, it is more animal than plant. The "bark" is a rough leathery skin, with lots of folds and wrinkles just like a swamp cypress.
It's flesh has many similarities with wood, being comprised with a combination of rigid walled cells and more traditional animal cells. The addition of many air pockets that can be inflated gives the anemone the structural support to stand upright without the support of water, but also the ability to flex and move if needed.

It anchors itself with many tentacle like appendages in the soil and which spread out just under the surface. These also act as a way for it to detect nearby movement.

"Branches and Leaves" enter image description here Likewise the "branches" are semi-rigid arms, and the "leaves" are comprised of dark green feather like structures. These feathers are not harmless plumage.
enter image description here
The calamus (hollow shaft) of the feather holds a quantity of toxin, and the tip is needle sharp. When prey comes near the tree it is felt by the tentacles under the ground, which are used similarly to trip threads in a spider web. The anemone then ejects dozens of feathers, which fall toward the ground like darts. A single scratch is enough to knock down a man sized creature, and stagger larger prey.

enter image description here
* Swamp anemone about to eat an unsuspecting man

The folds in the skin also conceal a mouth like opening. When the prey has been downed by the feathers, the anemone then pushes it's tentacles above the surface, grasp the prey, and shove it into it's mouth for digestion.

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    $\begingroup$ For an anemone-like creature, this sort of body plan would probably make more sense if it were a colonial lifeform, like the sea pen. $\endgroup$ – Cowrie Dec 21 '17 at 22:54
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The reaping willow has a most peculiar fruit, little wound-up coils of material that effuse a sweet, inviting scent, perhaps to entice, though also perhaps to help cover up the other odors that come from the soil below. When an interested animal gets close, sensors in the roots below detect the weight of worthwhile (sufficiently heavy) prey and the fruit rapidly uncoil (having been held closed by only a small trigger mechanism), dropping vines onto the surprised visitor.

These vines contain thousands of tiny stinging cells, similar to jellyfish nematocysts. They inject extremely potent toxins that rapidly immobilize their prey. The vines then naturally wither and fall off so that new 'fruit' can grow.

Of course a tree with obvious corpses beneath it might scare off future victims. This is where the tree benefits from its symbiote, the barkbrood ravager. This fearsome creature is a particular large species of ant and it has developed a very specialized relationship with the reaping willow. After paralyzing its prey, the willow releases from its roots a pheromone that acts as a dinner bell for its inhabitant colony. Thousands of ants swarm out and cover the paralyzed victim, injecting digestive compounds to liquefy its tissues for easier consumption. These compounds even help dissolve the bones, for although they are of limited use to the colony, their minerals diffuse into the soil for use by the willow.

Over just a few days (fair warning: time-lapse video of a gecko corpse being consumed by a swarm of ants), a grown man can be reduced to a layer of mulch. Organic clothing is also typically consumed, though more durable artifacts of metal or stone remain intact as warning markers for the sufficiently wary. The nutrients are carried by the ravagers to specialized root nodules around which the colony's tunnels are dug, which accept the raw nutrients and continuously secrete a sweet sap for the ants to consume when food is not immediately available. It takes a while for the willow to regenerate its fruit and prepare for its next guest, but its appetite for large meals more than balances this out.

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    $\begingroup$ On a side note, I recognize that this doesn't move the actual branches, but I find moving branches to be fairly implausible, as wood is not really intended to deform in the necessary ways. Mobile foliage, on the other hand, is very much within the realm of what plants can accomplish. $\endgroup$ – Dan Bryant Dec 21 '17 at 18:21
  • $\begingroup$ That video of the gecko is amazing! $\endgroup$ – Green Dec 21 '17 at 20:51
  • $\begingroup$ A tree fit to live in the Bonegrass Savannah!!! $\endgroup$ – Joe Bloggs Dec 22 '17 at 18:38
  • $\begingroup$ For anyone interested in the jellyfish nematocysts, Destin from Smarter Every Day has an awesome episode which includes seeing nematocysts firing in slow motion! $\endgroup$ – Cort Ammon Dec 22 '17 at 21:59
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    $\begingroup$ Is your reaping willow biologically a tree? If so, how does it map the location of sensory input (pressure) to the location of the branches/fruits, in an acceptable amount of time? Any stationary predator relying on large prey would starve after the larger animals of the area have fled or been eaten. For smaller prey (if detectable): As neurotoxins are generally expensive to produce, I doubt the energy input from what leftovers the ants carry to the root nodules suffices even for just regrowing the one fruit wasted on killing a hare or the like. How does your tree survive its early youth? $\endgroup$ – Orphevs Dec 23 '17 at 14:51
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The Greater Whipping Cypress

Any weapons system needs a way to acquire, track, engage and destroy targets/prey. Venus Fly Traps use sensitive hairs to detect prey then trigger the leaves to close over the prey. A cypress tree has a lot going for it. The Greater Whipping Cypress (GWC) will use elements taken from regular cypress trees, and electric eels.

The GWC lives in soft, water-logged ground. It has a deep and broad root system that interlocks with nearby trees.

Cypress Knee

Acquire & Track

Cypress knees stick up above the ground and make a convenient multipoint tracking system. Each of the cypress knees senses the electrical fields emitted by the nervous systems of all living creatures. When the electrical field is large enough and moving slowly enough, it triggers the trap.

Engage

Many earth species of cypress live in environments with large amounts of Spanish moss living in their branches. Spanish moss is normally benign but the Greater Whipping Cypress has evolved a mimic branch that looks like Spanish moss. We're going to refer to the imitation Spanish moss as Inquisition moss. When triggered, a clump of Inquisition moss drops from above onto the prey. Location information was provided by the cypress knees so targeting should be good. The Inquisition moss sticks to the prey, immobilizing it first with mechanical restraints then by strong alkaloid poisons. Strong digestive enzymes are also injected.

The Inquisition moss will need to be quite close to the ground to prevent wind from blowing the moss sideways when it falls. There should also be something to prevent the moss from falling if the wind is blowing too hard.

Digest

Given that the prey is already immobilized on the ground, it doesn't make a ton of sense to haul the prey back up into the canopy for digestion. The tree already has a vascular system for moving nutrients and water around so let's use that.

Growing new roots or enveloping the prey completely for full digestion takes too long. The Inquisition moss has little whips that activate on landing. Some go into the prey to inject the paralysis poisons and digestive enzymes while others push down into the soft ground. Just below the surface, the tree roots wait for the incoming nutrients. Even when the nutrients are injected into a part where the roots aren't close, the nutrients will stay around for the roots to grow out to them.

As soon as the digestive enzymes start working, the whips start moving nutrients from the prey to the waiting root system. Even if somehow the prey survives, the tree will have gotten some benefit.

When digestion is complete, the Inquisition moss disintegrates leaving the bones to be scavenged.

Defense against theft

Because of the close contact between the Inquisition moss and the roots, it's easy for a large amount of nutrients to pass from prey to tree.

The strength of the poisons used to immobilize the prey are such that any other scavenger that wants to steal from the Cypress will only be able to eat a small portion or none at all. Just as predators learn to leave skunks alone, so scavengers will learn to leave Whipping Cypress prey alone.

Clean Living Space

The poisons and digestive enzymes that leak out from the Inquisition moss into the surrounding soil suppress ground cover growth. The Inquisition moss requires a straight path to fall on the prey. Having other plants around would complicate this mechanism.

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    $\begingroup$ Spanish moss. Inquisition moss. I see what you did there... $\endgroup$ – DonielF Dec 21 '17 at 21:15
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    $\begingroup$ If scavengers are able to learn about this tree, wouldn’t all animals eventually learn its calling cards and avoid it? $\endgroup$ – DonielF Dec 21 '17 at 21:17
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    $\begingroup$ @DonielF not necessarily. It only takes a few clueless or unobservant animals to properly provide. It may just be a young bird, or perhaps something too busy frantically fleeing a predator to notice the one directly in front of it... $\endgroup$ – Papayaman1000 Dec 23 '17 at 15:58
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Supersized land anemones

Meet the swimming sea anemone:

Sea anemone swims away from sea star

It's desperately avoiding the grasp of a nearby sea star, which is interesting but not what we're interested in. Rather, notice how it bends its ring of tentacles nearly all the way to the ground.

What if this wasn't a defensive mechanism, but rather an offensive one? Our supersized land anemones would remain quietly waiting until they detect prey, either by touch or through the network of symbionts surrounding them. Once triggered, the entire crown of the tree, full of tentacles and the anemone's nematocysts, would smash down upon the prey, capturing it and lifting it into the forest canopy. There, the prey is digested exactly like a normal anemone, and the land anemone is ready to catch something else.

Considerations

It'll take a some handwaving to make this happen, but that's mainly to do with the transition of the anemone from sea to land. Anemones are supported by water pressure, so our land versions would only be found in the dampest areas such as swamps.

It's quite possible to imagine an anemone that ends up looking like a tree, especially if it's a strong evolutionary pressure. The stalk of the anemone might become tough, leathery and brown simply by drying out, giving a very bark-like texture. On land, zooxanthellae can be much more helpful given the higher intensity of sunlight, so they'd proliferate wildly. However, these symbionts are brown algae, so the tree canopy would remain a brownish golden color all year long, much like a sick tree.

Supersized heliozoans

Heliozoans are a class of aquatic predators that look like underwater spikeballs:

Heliozoan

They act almost like underwater spiders, as they use those long, thin spines to catch prey, which are nearly invisible underwater. They're coated in a sticky substance that may have some paralyzing effects. They sit and wait for a prey item to bump into a spine, at which point the spines actually retract with incredible speed- up to 2 body lengths per second. Prey is then brought near to the cell body and digested.

Fortunately for us, some species already come with trunks!

Stalked heliozoan

Such species rise slightly above the sediment and focus on plankton floating by. In a dark forest, it's easy to (not) see supersized versions of these creatures as they remain almost invisible amongst the trees- and horrific to imagine being dragged into the sky after touching what looks and feels like a spiderweb.

Considerations

Again, these are aquatic creatures that don't like being suspended in the air. Fortunately, they also have a sporelike function that they'll use when food is scarce or the streams dry up. It's possible that such a heliozoan, once left in a dry streambed for long enough, will nonetheless try to feed. Realizing the vast amounts of food available, they'll be selected for size and eventually (with a tiny bit of handwaving) become the size of trees!

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ya-te-veo - carnivorous tree

The Man-Eating Tree

The slender delicate palpi, with the fury of starved serpents, quivered a moment over her head, then as if instinct with demoniac intelligence fastened upon her in sudden coils round and round her neck and arms; then while her awful screams and yet more awful laughter rose wildly to be instantly strangled down again into a gurgling moan, the tendrils one after another, like great green serpents, with brutal energy and infernal rapidity, rose, retracted themselves, and wrapped her about in fold after fold, ever tightening with cruel swiftness and savage tenacity of anacondas fastening upon their prey.

Such a tree has existed in our imaginations. The question is what shape would this tree take?

Building a bigger Venus Flytrap

big venus tree

I've studied fascinating aspects of the venus flytrap and it's 20 second rule. The flytrap counts the number of times something touches the sensory hairs on it's leaves. If you touch one, it triggers the plant to a ready state. Touching two hairs in a short amount of time causes the trap to close, but not all the way. It leaves room for small insects to escape since it will cost the plant more energy to consume the prey than it produces. If you touch three hairs, the trap switches to digestion mode and with five hairs, it releases digestive enzymes. All of this comes from a plant with no nervous system, no muscles, we simply do not know how this works. What we do know is that each leaf can be used around three times before it dies off and the plant needs to create a new leaf.

With the need for a massive branch to be created to digest a man, it would require some really amazing growth. It would grow as fast as the fastest bamboo, yet be solid enough to support a man or large prey. I'm not sure it would be effective to have such massive roots supporting a branch and the large, tough leaves required to trap a man and hold him until digestion starts.

shrew on a raja pitcher plant

Pitcher Tree

I think a carnivorous tree would take the shape of a giant pitcher plant. It would resemble a tree like an oak, with leaves that would give it some nutrients. I don't think moving branches are realistic. I am not sure the physiology behind a venus flytrap would scale up.

The center of the Pitcher Tree would contain a sweet nectar, tastier than any peach, with an irresistible smell. It would use pheromones other species use for mating to attract prey into thinking this is a place for romance. Other plants like the titan arum do something similar to attract carrion beetles to help pollinate the flower.

It's prey would try and drink the nectar, lose footing and end up in a slippery, sticky pool with no escape. Eventually, the plant would sense the prey, release digestive enzymes to break down the flesh into usable nutrients.

I'm not sure how long a man-eating tree would last in the wild. One would assume nearby villagers would burn, uproot or do whatever they could to rid the area of such beasts. At the same time, I could see planting the tree around a village you did not like to be a very good way to send a signal to your enemy about how you wished for them to disappear.

Jimenju - human head tree

Good luck.

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I have two versions for you.


1 The answer you don't like

As Dubukay suggests, your anemone tree could resemble actual anemones on land. Instead of making the whole treetop one giant set of tentacles with the mouth in the middle, the tree could consist of traditional twigs and branches sporting small tentacle mouths. Each mouth would secrete a sweet smell , be brightly coloured to mimick flowers, or have other means of (passively) attracting prey. This would provide several benefits to the creature/plant:

1.1 Lower Energy consumption

Having the tree move around to catch prey is going to cost energy. A lot of it. Being able to move aroudn superficially while also being rooted underground makes no sense from an evolutionary standpoint, because the increase in range at a rather slow speed does not compensate for the loss of energy. An rooted organism capable of any noticeable controlled movement would either loose this capability, for example if the ground supplied enough nutrients, or loose the roots, in case the movement made up the central aspect of the organism's energy acquisition cycle.

1.2 More Consistent food supply

This is in response to some of the other answers submitted, where the tree preys on larger animals.

Predators that prey on large animals invest a lot of energy in hope of a lot of food (hyenas, wolves, lions), and will spend most of their time conserving energy if there is no food source in sight. Predators that hunt smaller animals (frogs, otters, smaller birds of prey) spend most of their time hunting, since each food ration they acquire will not last as long, but also is not as hard to get.
Since the anemone tree is most likely stationary, it can't search for food; it has to wait for it. As large animals tend to be rarer, I deem it unlikely that such a tree's prey spectrum would consist of anything larger than insects, rodents, birds, small monkeys and the likes. This brings us to the third point:

1.3 Higher likelihood of actually catching anything

As we've ruled out large (and therefore slow) animals, we have to acknowledge that out prey will be fast, faster than out tree can afford to move. Nature shows us that carnivores don't neccessarily have to be fast; there are a number of flesh-eating plants which rely on stickyness, stunning or sedation of the prey upon first contact to keep it in a place where the plant can easily digest it.


2 The answer you might like a little better

So, as the question explicitly asks for moving branches, we have to incorporate them somehow, despite their high energy consumption and low evolutionary likelihood. What benefits could the anemone tree gain from being able to move its branches, when it is a "passive predator"?

2.1 Fishing

While eerily waving vines might deter prey on land, it can be quite the attraction under water. Imagine a tree literally applying a longlining technique with its vines.

2.2 Photosynthesis

There might be not enough prey around, and in case the anemone tree is an actual plant, it could use it's movement capabilities to gain the most sunlight for photosynthesis, the same way people earlier thought sunflowers would do it.

2.3 Very slow prey

Its prey consists solely of slow and/or relatively blind animals like snails, worms, or turtles, so that the tree could graze a larger area for potential food. It's debateable whether a strand of sticky vines could retract with enough force to lift something as large as a turtle. If not, the question arises how the tree could access the food source after killing or immobilizing it with toxins; dragging it into the ground is hardly possible with anything but very soft soil, and would leave visible marks that would warn other prey. Leaving the carcass on the ground would mean leaving it to scavengers, and loosing a big part of its nutrients.

2.4 Symbiotic host

It has a symbiotic relationship with a species that can somehow supply massive amounts of energy for the tree. An example would be ants or bugs decomposing fallen prey. How the tree would benefit from the bugs taking the food is unclear though, as I highly doubt the feasibility of feeding nodules.

2.5 Free movement

Its actually not stationary. The anemone tree is by no means a plant and can easily pull its "roots" from the ground and move freely. Maybe the environment has a high risk of storms or floods partially, so that there would be a reason for the "tree" to lock itself in a stable position.

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I offer you my version:

The Octopus Willow

I thought of a tree similar to a Weeping Willow, with long, falling leaves that reach almost to the ground. These leaves are impregnated with a tremendously sticky substance, and react to touch.

So, when an unsuspecting prey crosses a curtain of its leaves, it ends up stuck to many of its leaves, unable to move. This is when the leaves react and retract by rolling on themselves, rolling the prey with it. The prey then ends up ont op of the tree, curled up in its leaves in a cocoon-like leave roll, similar to a fly curled up in spider web. The prey is now slowly "digested" by the tree.

A nice pro is that no visible corpses here, just strange non-corpse-like leave balls, up and away from sight.

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I think the first way to go about this is to address 'why it needs to even eat?'

Anemones eat for the same reason any animal does, because it cant make its own food.

Predatory plants, more famously the Venus Fly Trap, can make their own food through photosynthesis. The reason they eat animals is because their environment doesn't not contain usable nitrogen and phosphorus which they can get from flies.

This is important to address first because it determines what traits are needed and what the waste of the creature might be like. An animal can use all the nutrients in bones leaving dust or pellets behind however a plant likely wouldnt need the calcium so like the venus fly trap might leave desiccated bodies laying around which may be discouraging for larger prey.

For this reason I'm going with an animal as leaving bones behind would be bad. This also means it needs a rigid calcium based structure somewhere like the trunk. Calcium structures are vulnerable to water so it needs a protective layer like a keratin layer that appears like bark. Keratin is the substance found in finger nails and animal hooves that is strong and water resistant. Good coincidence is that hooves bare similar color appearance and rigidity to bark.

Now the big question is "how does it digest?"

Anemones aren't capable of a lot of motion, moreover what motion they can perform is often supported by their aquatic environment. Additionally, the point of this topic is to have passive predatory creature.So whatever predatory method is used on land must work with gravity. Therefore this creatures stomach must be at its base / root system. It must also have a way of hiding bodies.

So I purpose: the 'root' structures are capable of hollowing out a large pit around the base of the 'tree' and expanding into the pit walls to support anchoring. A secondary more fibrous root contains barbs like the anemone that secrete acidic toxins capable of melting prey. At the base of the pit resides more absorptive roots capable of transporting all that material up the tree. Basically falling into this pit would be easy but the viney stinging roots would ensnare and prevent fauns from escaping.

(Note: The roots need not contain paralytics because the paralytic leaves, discussed later, would be present in the pit. This allows for more digestive specialized 'roots')

Now what to do with the waste?

The tree transports the nutrients up the tree and deposits waste into large leaf like structures that don't perform any photosynthesis. when its foliage reaches a certain density it releases them with some being carried off with others falling onto the root pit making the perfect pitfall cover. The fallen leaves obscure the pits opening from sight of unsuspecting ground animals which can fall in like a pitfall just by passing by.

At this point we have a tree like creature that can already catch some animals but we want it to be a little more proactive.

How does it hunt? couple ways,

  • the leaves can contain micro barbs and paralytic sap. Since the tree doesn't care about the leaves it can easily lose them, so if an animal touches the leaves the barbs make the leaf cling to the animal so that even if it breaks free it still has this leaf clinging to it while the paralytic sap continues to soak into the skin aided by the perforations of the barbs. This would get anything landing on it or trying to eat its leaves if they hadn't fallen into the pit already.

  • the paralytic sap can also be volatile. On particularly hot days the sap can vaporize from the leaves creating a paralytic gas cloud over the tree. This would cause near flying birds to fall into its realm.

Note: this sap only needs to be paralytic causing the animal to fall into the root pit.

  • It can produce a flower that is not needed for procreation but simply looks vibrant and releases a sweet smell in order to attract pollenating prey.

  • It can also produce a fruit. The fruit need not be insidious as the rest of tree is plenty insidious as it is. Instead the fruit would likely be kept towards its center and be used for reproduction. If it manages to get carried off then it successfully procreates if not then its mature stage can be some floaty structure like a tumbleweed that can carry it away from the root pit.

'This sounds too passive'

Unfortunately the structures that give fly traps and anemones any kind of motion do not scale well to land based tree sized structures for large fauna sized prey. Lifting something the size of a deer requires to much motion so its better to rely on passive trapping as much as possible.

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  • $\begingroup$ The specialization of the various structures is key here because the more task specific a structure is the better it can adapt to fullfiling that purpose. Like the leaves can adapt to making a plethora of paralytics to catch a wide range of animals. while the roots can focus on digestion and structure. $\endgroup$ – anon Dec 27 '17 at 17:12

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