Generally speaking, plants get filed under the "boring" category. Occasionally, they smell nice, look pretty, or provide some tasty food, but that's about it. Until you realize that these immobile life forms are engaged in a terrifying daily battle that involves theft, slavery, eavesdropping — and explosives.
Plants face a pretty unique set of challenges. Throughout their lives, plants don't have much say in where they live. Seeds are scattered by wind or animals, and may end up in useless wasteland (game over). If a seed is lucky enough to germinate, it is stuck in the same spot for the rest of its life. All of its food, water and light are supplied only by what it can reach with its roots and leaves, if other plants don't get it first (game over). And then there are the predators. Nematodes, insects, birds, mammals…all munching plants to the ground (game over) before the plant can achieve its ultimate goal: a sexy encounter and reproduction.
So how do plants cope?
Exploding Seed Pods and Self Planting Seeds
One of the biggest challenges plants face is getting their seeds somewhere safe, and far enough away from mom that offspring don't have to compete with their parents (or share their diseases). If your seeds are light-weight, you can float them away on the breeze (think dandelions), but that doesn't work for heavier seeded plants. So, some plants have evolved explosive propulsion. These plants have specially formed fruits that, as they dry, create a tension that explosively opens seed pods, sometimes tossing seeds as far as 200 feet, and with force enough to crack an oak plant press!
Some of these plants employ both ballistic seeds, and create seeds with similar structures that twist while drying, effectively causing the seed to bury itself.
Tricking Ants into Planting Seeds
Ants and plants have a long history. Long enough that many plants have evolved specialized structures to get ants to work for them. One such structure is a delicious little packet of fatty tissue on their seeds, called an elaiosome. Ants grab this tasty snack, drag it into their nest, feed it to their offspring, and discard the seed in an empty chamber, effectively planting and keeping it safe from predators.
Photo by Benoit Guenard
Tricking Ants into Killing Enemies
Ants are pretty territorial. If you give them a nice house to live in, or a delicious sugary drink, they will defend that house or beverage to the death. And plants know this. So they have evolved special structures that invite ants in to live, called domatia. These specialized structures are evolved to provide inviting homes for stinging ants. On the acacia, these domatia often form on thorns, and when large mammals come to graze on the plant, the ants swarm out to defend their home, stinging animals that might otherwise munch the plants.
Plants have also evolved specialized ant-feeding structures called extrafloral nectaries. These little bumps and nodules secrete sweet nectar, which ants love. In an effort to maintain control of this sweet food, ants aggressively defend the nectaries, chasing away insect predators and sometimes even beneficial pollinators.
Believe it or not, plants have a lot of decisions to make. Do they make more leaves,to harvest light, or more roots to capture water? Plants have to do both just right in order to reach maturity and reproduce. And for some plants, that is, frankly, too much work. Take for example, the golden paintbrush. This plant can be self-supporting, collecting its own light and nutrients, but give it half a chance, and it will extend its roots toward its neighbor and form special structures called haustorial connections. These links allow it to tap into the roots of other plants, stealing water, sugar and nutrients. And, like a good parasite, these plants don't usually kill their host but instead, leech off of them for years.
Plants can pick up important information by tuning into what is going on in their immediate vicinity. Like a neighborhood watch forming after a break-in, plants pay attention to the distress of their neighbors while they are being eaten by predators, and mount their own special chemical defenses. Plants that are being eaten tend to release volatile compounds (responsible for the smell of cut grass, crushed sage, and basil) in part to ward off insects. Plants nearby can detect these compounds, and begin to sequester bad-tasting or poisonous chemicals in their leaves to deter herbivores when they move on to the next victim. Scientists have shown that plants who experience these warnings receive less damage from predators than those that haven't. Some plants also use these signals to change their sex in response to neighbors. For example, if a plant is located in a neighborhood full of female plant chemicals, it may devote its reproductive efforts to making sperm rather than seeds, in order to guarantee successful reproduction.
Tricking Insects into Sex
Sex in the plant world is a whole lot less sexy than it is for most animals. For the most part, plants never meet their sperm donors because plant pollen (yep, that is plant sperm all up in your nose causing your allergies) is typically blown around by wind or carried by bees and birds from flower to flower. Sometimes, just getting the correct bird or bee to stop by your sexy flower can be difficult, if your nearest partner is hundreds of meters away in a dense jungle. And reproduction is the end-goal for plants.
So evolution provides. Mimic orchids do exactly what their name suggests: they mimic the appearance, and in some cases, smell, of female insects. Unsuspecting male insects are easily fooled, it would seem, and can spend several vexing minutes humping a flower, only to realize that seductive lady is actually just a plant. However, while Mr.Bug was trying desperately to get it on, the orchid has attached a special pollen sac, called a pollinia, to the insect. When the poor guy finally gives up and flies off, the pollen is attached, and will detach when the next nearest orchid tricks him again.
This mimicry can lead to some interesting results for scientists when bees go extinct, as highlighted in this wonderful XKCD comic.
When we consider the struggles of the plant, it becomes pretty apparent that they are not boring, but are in fact awesome. They can be pretty dynamic, in some cases growing up to a foot a day, poisoning their neighbors, or being downright terrifying, like when they eat mammals. Not to mention breathing in our gross mammal breath and turning it into delicious, life-giving oxygen. Do yourself a favor, and get a pet houseplant.