25 million years PE, the mutualistic relationship that has developed between certain genera of leafcutter ants and several species of bamboo has produced a radiation of wildly successful new species that exist in symbiosis with one another.
By the end of the Hypostecene, a distinct example of mutualism had already begun to spread across the world's forest ecosystems, where colonies of ants and bamboo plants had begun to adapt towards each others' benefit. The ants protected their host plant, known as a myrmecophyte (literally "ant-plant"), in return for a safe and secure place to call home, driving off other insects and keeping their home plant safe from threats. In the following ten million years this process has continued to an even greater extent. A new genus of ants has become obligatorily tied to a newly-evolved radiation of bamboo plants that no longer spread significantly by rhizomes into colonies, but instead grow single tall trunks which grow a radiation of secondary branches at every leaf node, eventually developing a pyramidal shape reminiscent of a pine tree with only a single leading shoot. This single tree lasts several years before flowering magnificently at its upper growing stem but a single time, producing seed, and then dying. These single-stemmed, tree-like bamboos grow more slowly than their clumping relatives and most other tree-like plants, which would normally put them at a distinct disadvantage in a high-competitive world, but these plants have a secret weapon: they grow large and extremely thick knots near its base and throughout its root system in which their symbiotes dwell.
The knots are hollow, providing a perfect environment for the leaf-cutter ants to cultivate their fungal gardens, relatively safe from predators as well as the weather. No longer needing to dig their own burrows, they cultivate their gardens in pre-built beds, leaving them more time for other occupations, such as defending the host tree from all threats from tiny beetles to giant browsing birds. Any creature which attempts to feed on the host plant in which the ant lives is mobbed in mass and bitten with giant mandibles and stinging bites. Additionally, however, simple defense, already having been practiced by many species for several million years, has in a few new symbiotic relationships becomes active offense.
As previously described, leaf-cutter ants have existed in symbiosis with bamboo for more than ten million years by the middle Tempuscenic. Many species of ant still behave similarly to these ancestors, feeding on their neighbors and defending their hosts by attacking hungry herbivores - even other colonies of their own species on neighboring plants. There exist constant battles waged by the bamboo with their own insect armies that each exhibit specific castes adapted to either attack threatening animals or to clip vegetation.
The Monovitus bamboo, however, does not grow where bamboos historically have. With its single trunk and slower than average growth rate, it has begun to adapt to a drier climate than most of its kind can tolerate. It moves onto the dry uplands where the sunflower trees thrive, storing energy in a strong taproot. The sunflowers are more abundant and grow faster than the bamboo and exude harmful tannins into the soil in attempt to stunt its growth and crowd out the competition - but the Monovitus has a solution. Its own leaves are thin, hard, and succulent, almost needle-like to survive in dryer environments, and with bitter alkaloids they are highly unpalatable to the particular genus of ants adapted to live within it. Even if several trees grow near each other, their ants do not battle. Instead of foraging from their own host species, the logger ants, with shearing mandibles for pruning plants, cooperate to search out more succulent foliage, and nothing is more succulent than the soft, broad leaves of the sunflower trees. As the secondary branches of the bamboo tree spread out in a whirl in all directions around the trunk, they regularly come into contact with surrounding sunflower trees that the ants then feed from, cropping the green leaves and taking them down to their burrows in the bamboo's roots to feed their fungus gardens. Unlike other bamboo, the sunflower trees have not adopted their own armies of protective ants and have no defense against such a systematic attack. All around the tree, the ants obliterate the surrounding vegetation, completely defoliating their host tree's competitors, cutting off their flowers before they bloom, and eventually killing them. Occasionally a brushfire burns away all of the food around the tree, sending the dry stalks of the sunflowers up in smoke, but the Monovitus survives by merit of its hard, dense wood. After a fire, its thin leaves are quick to regrow. In the intermediate period where its ant colony has nothing to forage, they turn to feeding on the nutrient-rich tissues of the host tree's root nodules, sufficiently nutritious to sustain them until their preferred food regrows around their host.
Within approximately ten years, a colony has often cleared a circular space of more than ten meters around, or the approximate spread of its host's branches that now fill the empty space lushly and enjoy a bright spot in the sun. By this time, however, the squat, sprawling tree that now reaches perhaps five meters in height begins to stop growing. Its ant population having ground up all of its competition into a fine compost and deposited it at its own roots, it now sits on an enormous store of nutrients that it uses to produce a magnificent spike of flowers more than thirty feet above its branches, the blossoms cascading nearly twenty feet around from its topmost point in a splendid display. The show lasts for just three months before the flowers, pollinated by the wind, fade and large, hard seed pods take their place. Eventually the pods burst, revealing hundreds of thousands of fluffy, hair-covered seeds, each equipped with a white wisp of fiber that will carry it on the breeze. The seeds are hard, few birds favor them, and the majority float away on the wind. When the seeds mature and are shed, the bamboo dies, its life's work complete. Within a year its needles wither, its secondary branches drop to the soil, and eventually only a dry trunk remains like a monolith surrounded by vacant soil and short grasses. When the tree dies, the ant colony follows. Once their host's branches wither, they are isolated in a veritable desert. They consume the roots that once provided them shelter, but as the tree has since died, they have become dry, almost inedible, and when used up don't regenerate. Eventually, there will be nothing left to sustain the colony and it will collapse. Just before all is lost, the colony reproduces for the first time. For more than a decade it has produced workers. An extremely long-lived queen has laid hundreds of million of eggs in her lifetime, all of them infertile female workers. Now, tired and aged, she produces one last flush of eggs to be nourished by the last of the worker ants. Hormonal changes brought by the shortage of food result in a different crop of offspring this time - a swarm of flying queens and drones (fertile males and females). The winged ants take to the skies in search of a new home while their elders and their tired mother, without food, slowly go still and die beneath the roots of the great tree that sustained them for so long, their lives - but also their life's purpose - completed.
The kings and queens are hard-wired to search for a new Monovitus tree in which to begin a new colony, but only a very young tree, just a few weeks old, will suffice. Any older and a tree will surely be claimed by an established colony. How possibly do the tiny ants, who have just days to find a new host before they starve, locate such a perfect tree?
They use their noses. Not for the tree's specific scent, no - this would more than likely lead them to a mature tree already taken. They instead search out the scent of a recent brush-fire - charcoal and burned carbon. Fire is relatively rare in most Serinan environments, but in the dry forests it is a relatively common fact of life. Given the rapid growth rate of the sunflower trees, it is only when an entire forest has been cleared by wildfire that the seeds of the Monovitus tree stand a chance to establish themselves. Of countless thousands that floated all around from the now-deceased host tree, by chance one or two will surely have landed upon a patch of ground that would, before too long, be scarred by flame. Only when exposed to the extreme heat of a brushfire will the Monovitus tree's seeds germinate. Then, briefly free from competitors, the tree has several weeks to sprout and grow as fast as it can before the sunflower forest begins to sprout again around it. By the time it does, as much as two years after its parent tree flowered and began to die, it should be just around the time that the mother tree's colony will have produced its flush of new kings and queens in search of their own new little tree to call home. Dozens of the kings and queens released from the aged mother tree all hone in upon the new seedling bamboo tree, often the only one of its rare kind for miles around, fighting over squatting rights. Eventually only a single pair will take dominance in the first, smallest root node of their new host (but eventually, if another tree is nearby and the two come to grow together, multiple colonies will join together.) The little family will begin to breed, the flying male at first leaving the tree to distant greenery to bring back leaves to start a fungus garden before the other plants begin to return nearer to the colony. When the burned ground around the new tree begins to turn green with a new flush of vegetation, the male dies and the first flush of female worker ants - just a few of millions to come - take over foraging. As they prune away the little tree's competitors and fertilize its roots with compost, it grows steadily larger, sprouting additional hollow root nodules to support the new and growing ant colony. The cycle begins anew.