150 Million Years Post-Establishment
Assassin grass, gluetrap trees, and an ecosystem once more in flux
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We are now in the late Thermocene. Serina by this time has had more than one hundred million years of relative stability, with a stable climate well-suited to the long-term survival of many plant and animal groups. Now, however, a newly emerging plant group threatens to completely overturn everything, and it has only existed for less than one million years.
Assassin grasses are a newly evolving genus of tropical and temperate grass which have evolved a very dramatic and effective manner of reducing their competition upon the grasslands where they originate. They have evolved to produce a powerful natural herbicide in their leaf tissues to which the assassin grass itself has evolved immunity. The leaves of assassin grass are edged in small, fluid-filled beads which are easily ruptured, leaking a clear, odorless fluid containing the compound. The beads are popped easily by the movements of animals, but this isn't their primary function. Their main use is to be abraded and broken by the harder, silica-edged leaftips of other grasses when they come into contact, releasing the harmful agent which then bleeds freely and is absorbed into the competitor's leaf tissues, causing die back of the affected stems within several days wherever the assassin touches. The herbicidal agents at use are several closely related chemicals known as sulfonylureas, which interfere with the synthesis of amino acids in most other plants which have not developed a natural tolerance, slowly causing them to wither and die. Though deterrence to herbivores was likely not the primary reason for the assassin grass to develop its defenses, an added benefit of the chemicals is that they are also potentially harmful to animals by inducing hyperglycemia - high blood sugar. Though the grass is not immediately toxic to animals and can be eaten in small quantities without lasting harm, grazers which feed extensively in areas where assassin grasses have displaced most of their competitors for a prolonged period of time are at risk of being sickened and eventually put into hyperglycemic shock. Animals would thus instinctively avoid assassin grasses all together unless they have exhausted all other available forage, leaving its growth largely unchecked and furthering its ability to spread.
Because assassin grasses have few competitors and few animals feed on them significantly if given a choice, they can take over large tracts of open habitat and are a highly successful pioneer species, one of the first to appear and spread after natural disasters, such as fire or hurricanes, that clear large areas of other plant life. They have an effect too upon natural forest succession, for the young of trees and forest-forming plants experience extreme difficulty in establishing themselves in the presence of assassin grasses, which abrade their tender new leaves and poison them as they germinate and reach up to the sunlight. For the past half million years that the assassin grass has existed in its modern form, its offensive adaptions have given the assassin grass an extraordinary advantage over other plant life, so much so that across Serina many millions of acres formerly covered in diverse forest ecosystems have been displaced by at times seemingly endless prairies of this toxic invader, which may now comprise almost 99% of the floral biomass in some environments. Though the seeds of assassin grass are edible to birds, few other large animals can survive well in these environments, meaning that the prairies are a sort of ecological desert, destroying biodiversity wherever they spread and threatening a great deal of Serina's endemic plant and animal communities.
Now, however, this is just beginning to change. Diversity is making a comeback as grasses of other lineages - grasses much more palatable to grazing animals - are returning to the plains, having evolved their own resistance to the toxic compounds produced by these new invasive species. A single forest tree has also emerged with a resistance to sulfonylureas. A member of the broad-leaved sunflower tree family, it superficially resembles a maple, with a fast growth habit, branching crown, and large lobed leaves. It produces edible seed pods favored by many woodland animals. Unlike some of it kin, it doesn't utilize ants for protection but rather produces a thick, sticky sap which insects struggle to chew into without gumming up their mandible or clogging their spiracles and suffocating, but which isn't inherently toxic and is easily broken down by the digestive systems of most higher animals. Aptly called the gluetrap tree, it is descended from a hardy understory bush which survived in the shade beneath the canopy and is thus able to germinate and survive even in tracts of dense assassin grass which block most light from reaching the soil beneath them. Able to sprout and develop slowly until they break past the dense crowns of the grasses and into the sunlight, forests of gluetraps then can grow rapidly, eventually producing their own thick canopy of branches which envelop the grass in shade. Adapted to the open plains, the grass cannot survive under shaded conditions and soon dies out, then freeing up the forest floor for the growth and establishment of other jungle trees including other sunflower trees which are involved in symbiotic relationships with ants.
One type of plant which does not survive well in these forests, however, are the myrmecophyte bamboo trees, which are for the most part naturally adapted to be pioneer plants and struggle to establish themselves in the shade of grown trees; even types adapted to grow in the understory for a while as seedlings are usually displaced, eventually, by long-lived sunflower trees as a forest reaches it climax state. Across Serina, for the first time in more than sixty million years, the global forest ecosystem is beginning to experience new and significant change. The highly diverse bamboo trees, formerly Serina's dominant plant type, will be almost fully displaced by the sunflower trees over the next twenty five million years. Their decline will be rapid and dramatic, paved by the spread of the gluetrap trees, eventually leaving them to persist only in their most specialized niches. Some of the lucky ones which will make it past the sunflower tree speciation boom are the bamboo mangroves and their derivatives, the true sea bamboos, which have managed to exploit niches outside the ability of most of their competitors to survive. Ant symbiosis will survive in a degraded state within the sea bamboos, with the sea ant, and within some sunflower trees, which originally developed the mutualistic relationship for the purpose of competing with the bamboo ant-trees which will experience a dramatic decline of diversity across most of Serina by the end of the Thermocene.