Trees of the Pangeacene

Myrmecophytes - broadly known as ant trees - have seen a resurgence as the dominant floral group making up the forests of the Pangeacene. Descended from sunflower trees and with no biological relationship to the original bamboo trees which first developed the mutually beneficial relationship, they adopted it as a result of their competition in order to defend themselves from other trees whose ant colonies would attempt to mow down all other plant growth in the vicinity of their hosts, unless those hosts could defend themselves. While some of their relatives, the gluetrap trees, instead developed sticky ant-smothering sap to protect their assets from injury, the easiest solution for other sunflowers was simply to accommodate their own ant colonies to limit the damage inflicted on them by those allied to neighboring trees. They developed similar hollow galls in their tissues to accommodate nests, and in some cases nectar-producing glands to provide a ready food source, to attract their own lodgers. Over the eons, these copycats would come to displace the original bamboo trees, which were afflicted heavily by the evolution of assassin grasses in the Thermocene which overtook large tracts of formerly forest habitat by inhibiting the survival of most tree seedlings. By chance, it would be a member of the sunflower tree lineage which first developed an immunity to the toxins produced by assassin grasses and was able to rise above them and shade them out, restoring forest communities. The tree in question was of the gluetrap lineage, and lacked ant partners. By beginning the chain of forest succession, however, it cleansed the land of assassin grasses (which die in shaded conditions) and allowed the subsequent growth of less resistant plants, including mymercophyte sunflowers. Before the evolution of assassin grass and gluetrap trees, it was the bamboo ant trees which had specialized as pioneer species, the first to grow on cleared land and start the development of the forest community - like assassin grass, they required full sun to grow and survive, and their seedling could not survive in the understory of an established woodland. So displaced as they now were by gluetrap trees that even following the decline of assassin grasses, there was little room left for their group. The extreme ecological upheaval at the end of the Thermocene, which resulted in the nearly complete loss of forests worldwide, was the final nail in the coffin for a once widely diverse group of trees, but was only the final factor following tens of millions of years of drawn-out decline.

The sole survivors among tree-like plants, excluding the extremely specialized marine bamboo which were by this time only trees in the broadest sense, descended from woody plants but now more akin to seaweed - were only a handful of sunflower species. Some of them were mymercophytes and utilized ants to trim away competitors and to spread their seeds. On the other spectrum, at least one species was a gluetrap tree which defended itself from said ants with sticky insect-snagging sap. It is these few trees, apparently all ancestrally tropical, which have given rise to most of the broad-leafed trees of the Pangeacene - thousands of endemic species worldwide. In the impoverished environment of the early Pangeacene, ant trees were extremely successful, employing their insect lodgers with the task of trimming back the leaves of any neighboring plants to maximize the amount of sunlight that could reach those of their hosts. This behavior evolved long ago in herbivorous, leaf-cutting species which would use the foliage of their neighboring trees to raise fungi, which they fed on. Most symbiotic ants of the Pangeacene, however, are more generalized. They still harvest the leaves they take and use them to raise fungal gardens which they harvest and feed to their larvae, but as adults they also feed on other insects, simultaneously keeping their host trees free of both insect pests and plant competitors. Additionally, the inner linings of the galls the trees produce to attract nesting ants absorb the nutrients deposited within them by the ants' droppings and partially consumed food remnants and the decomposing plant material utilized by the ants to cultivate the fungus they feed to their larvae. By associating with the tree, the ant is provided safety and a ready supply of food - so long as it does not consume its own host, but only neighboring plants, which the ants can distinguish by scent even among the same species. By attracting the ant, the tree benefits from the processing of the insect pests and plant competitors which would otherwise harm it into organic matter it can use to fertilize its own growth. The system remains highly beneficial to both plant and animal and lives on, even though the original bamboo trees which began the process have long since died out, survived only by the sunflower trees which, initially, were the very unwelcome competitors they employed the ants to attack in the first place.

Like the most derived bamboo trees, many ant trees rely on their partners to disperse their seeds. Seeding is timed with the production of fertile queens and drones within a colony, and each queen takes with her a seed when she flies off to start a new colony. Colonies start in the ground, where the queen buries the seed, but with luck, within a year it will be underneath the roots of a growing seedling. As the tree grows, the colony expands above ground and moves into the hollow chambers and galls produced in the tree's tissues, often channeling out highways just underneath the bark that stretch from the roots to the tops of the tree. Through these channels the ants cart food and leave droppings absorbed by the plant, in addition to a very large source of nutrients deposited in the underground nest chamber which the tree surrounds with fine feeding roots.

Sunflower trees are not the only tree-like plants around by 40 million years into the Pangeacene, however. In drier and colder regions where competition is much lower, myrmecophytes are less successful and other plant groups lacking either an insect-repellent sap or their own ant armies have been able to establish a hold, producing large tree-like forms. In the arid interior, these are the cactus sunflowers, related only distantly to the broad-leafed trees. Many species of them lack leaves altogether and grow only as of branching, thorny, water-filled photosynthesizing stems, some of them reaching heights of fifty feet or more - resembling a leafless broad leaf tree all year long. Others grow flushes of leaves seasonally, replacing them with sharp thorns after the brief rainy season to prevent desiccation, while a few groups retain their leaves all year long, covering them in a thick armor of hard silica; it is from this group, comprised mostly of desert bushes and small scrubby trees, that the creeping razorgrasses evolved.

On the plains and at high altitudes, dandelions regularly give rise to large and sometimes branching forms which could be considered trees of a type, though more akin to palms than anything else. On mountains, these are often the most noticeable endemics, swelling to massive sizes with large fuzzy leaves which insulate against the cold and airborne seeds that disperse via cottony threads on the wind, as they have now done for hundreds of millions of years. Dandelions are a plant group which seems very capable of producing large tree-like forms and have started on that path repeatedly throughout Serina's history, but never to their fullest potential, because they are always slightly less competitive than the other plants around them. In a world without sunflowers or bamboo, the dandelion would surely be the dominant forest-producing plant, but so far, most species must be content as smaller bushes and extremists, reaching their greatest sizes only where their competitors struggle to grow. Hardiness is certainly one factor they have going for them, the group as a whole being extremely tolerant to sandy and rocky soils low in nutrients and blazing direct sunlight - indeed, like bamboo, they struggle to survive in shaded conditions, particularly when first establishing. Dandelions thrive in the arid interior as a variety of scrubby bushes and daisy-like flowers which spend most of the year as dormant roots, bursting into bloom for only a short period whenever the rains fall. Some species have swollen leaves in which they store water, resembling aloes.