The end of the Mid-Ultimocene ice age has resulted in the proliferation of lush plant life across regions that lacked it for millions of years. Yet slower to adapt than animals, only a few species will go on to form the foundations of the new ecosystems of the future.
1,000 years have now passed since the end of the Mid-Ultimocene. An enormous cross-continental coal seam fire still smolders beneath the ground of Serinarcta, and will continue to burn for tens of thousands of years before it at last exhausts its available fuel supply. Yet the deadly surface fires, that once flashed across the land with deadly speed, are now a thing of the past as a much more humid atmosphere resulting from a massive increase in melted water and an atmosphere high in greenhouse gases now means that any which escape to the surface are doused quickly by rainfall. Over the land green vegetation now grows nearly to the poles, and there is already little seasonal change even at high latitudes. Global warming has come so rapidly that though most large animals that survived the initial fires have survived through behavioral adaptability, most terrestrial plants of the ice age have now died out.
Floral diversity worldwide is now dominated by just a couple of small, rapidly-growing species which have best been able to adjust to a suddenly much warmer and wetter environment, and nearly all plants that now cover the globe descend from short-lived annual plants, most of which had lain dormant as seeds for thousands of years until the permafrost melted and exposed them again to the surface. Puffgrass, a sedge-like, water-loving grass that evolved in the Pangeacene is the clear winner, and has colonized the entire world through its airborne seeds and spread in vast monocultures over all of Serina’s land. It shares its space here and there with a few creeping, relatively primitive descendants of dandelions and clovers. Cactaiga, a cold- and arid-environmental specialist that cannot survive wet roots, is in drastic decline, and with its loss the ancient lineage of sunflower trees is now nearly gone from the world.
But not entirely.
A singular species of myrmecophyte sunflower tree has also survived through the ice age and into this new era, living in the literal shadow of larger relatives. Just a few inches tall and with no woody trunk to speak of, the hiddenwood is the only living species of ant tree, a group that otherwise died out at the start of the Mid-Ultimocene ice age. It survived the cold and constant grazing by thorngrazers by adapting to grow most of its structure not up into the sky but below ground, as a hidden creeping rhizome. When damaged by grazers, these plants could quickly sprout new leaves low to the ground and so survive while smaller competitors like grasses were killed entirely either by grazers or by fire, though they barely managed to set seed and so relied on vegetative reproduction to spread, forming huge underground clonal colonies millions of years old. Hollows within the underground trunk housed its obligate symbiote, a small colonial ant, from the harsh weather of the ice age. These cold-hardy, slow-moving ants fed upon thorngrazer droppings, and by breaking them down into smaller particles, their own droppings then fertilized their host plant.
With the climate now warmer and nimicorn thorngrazers abundant, while the more destructive razorbacks have died out, this unique relic of an otherwise extinct ecology, along with its ant partner, is now reproducing again. Like distant, far taller forest-forming ancestors, the hiddenwood produces not seeds but fully-formed little plants at the edges of its flowering stalks. Large queen ants, much bigger than the tiny underground workers, take plantlets with them as they fly off to mate and to start their own nests and so plant them in safe places that are also loose and easily dug. They favor sites along steep riverbed slopes where there is abundant water, and where thorngrazers will struggle to reach them to eat them before they are big enough to survive being nibbled. For their first few seasons they colonize the riverbank, growing short prostrate stems and small green leaves, while their subterranean branches penetrate deep underground and eventually sprout new growth upwards and away from the riverbank. Now big enough to endure grazing, they eventually creep away from the site where they were planted and spread out to form large colonies that can now compete with faster-growing but far shorter-lived grasses. Thus is established the two major ways plants will survive the coming eons - quick to grow but short-lived, or slow to start but lasting for many years.
There are other persistent hold-outs from warmer days before the ice age, too. The ramblerooter is another small woody plant, like a bush or short vine, that has survived similarly to the hiddenwood by forming creeping underground stems. The ancestors of this plant, too, were trees, though never of as much significance or great size as those which descended from sunflowers. It is a member of the clover lineage, and its leaves still grow in groups of three. During the floral radiation of the early Pangeacene, its small prostrate ancestors rose to some success as small, fast-growing understory trees that formed colonies by spreading with arcing branches that gradually bent down and rooted into the ground at their tips, these rooted stems then growing upright again as another plant.
Ramblerooter ancestors survived into the Ultimocene with very reduced diversity, having been largely displaced by ant trees, but outlived most of them as the climate shifted severely in the ice age. Freed from these competitors, they now faced new threats from new groups of destructive grazers and climate changes, became smaller and shorter as the world got colder and harsher. At the height of the glaciation only one species remained, limited to the coastal steppe of Serinarcta, where its stems grew no more than 3 inches above the ground and crept almost entirely horizontal to avoid chilling winds and hungry herbivores. As in hiddenwoods, sexual reproduction virtually stopped for millions of years, except perhaps in brief and uncommon warm spells, and these plants survived by spreading clonally, with most of their growth at ground level and their green tissues short-lived and relatively disposable.
But now the weather is warm, and the winds have died down. The rambleroot's shoots, each one functionally like its own tiny tree, can grow taller without their oppressive force, reaching knee-height before they arc downward and take root. It spreads faster, and it has begun to flower again, exchanging stale genes once more and improving its vigor, and produces a characteristic jellybean-sized and shaped fruit with a single large seed, which birds spot and come down to eat. The seed is dispersed through their droppings anywhere they may fly away and land - even an ocean away. As seeds take root upon the thawed southern continent, and find themselves in a new environment with less intensive grazing than that from whence they evolved, the sky is the limit for how tall it might soon be able to grow.