Psilogrodendron

Psilogrodendron latacephalo
Psilogrodendron latacephalo and Aliqualignum ramyrtus

After seven-hundred million years, Earth will have become a distant place, geologically and biologically. It has evolved and changed for longer than today's animals had backbones. As life recovered from a prolonged mass extinction with a magnitude of no other, the center of biodiversity shifted to the land once the ocean gradually evaporated down to the reserves of their deepest trenches, ravines with highly-salinated water fed by Earth's new water cycle in a hot, humid, dying planet. Above the ground-shading bodies of permanent clouds, humid enough to support the microscopic producers that tint them green, the Earth's average temperature exceeds 170° Fahrenheit (75° Celsius).

Although the beginning of the era of springtails like Gnathosimilidon gorgops was characterized by a lack of greenhouse gases and its bitter cold, it ended with a Great Broiling as quickening hydrogen fusion processes in the sun expanded its luminosity upon the ever-changing planet. Trees grew structures of bark over them to shield their leaves from the sunlight, but all vascular plants perished within a span of roughly 100 million years, from a combination of lowered carbon dioxide concentrations and constant heating that further inhibited photosynthesis. Left behind were blind, microscopic eyeless underground nematodes sheltered from the worst of the radiation; phytoplankton that reproduced quickly enough to adjust to the ocean's heightened heat and sodium concentrations; planktonic organisms that fed on the phytoplankton and adjusted to the same conditions; heat-tolerant, algae-holding lichens that supported their symbiotes, even through humidification and desiccation, and grew with no noticeable change for hundreds of years; and various microscopic algae adjusted for thriving in the Earth's high temperatures, some of which became incorporated in the structures of surviving lichens. After the die-off of the last complex plants, no organism grew larger than a penny for the next 20 million years.

Over the period of time that Earth supported less ecological diversity than a typical man-made city, the hardiest and slowest-growing organisms silently adapted to the new conditions. Much more quickly than the second-worst die-off of multicellular eukaryotes began, it ended. A lineage of crustose lichens acquired the right set of mutations to take off, to diversify, and a Cambrian-Explosion-type diversification took off on land. Lichen with heat-tolerant proteins shoot up in size, transforming into tree-sized producers after previously having been no taller than a few millimeters. Blind nematodes take on a variety of diets and body shapes thanks to the burst of new life-supporting producers in a water-filled atmospheric Earth.

Even in the diorama 720 million years in the future, life has not stopped changing. Psilogrodendron latacephalo, the ecosystem's dominant tree lichen species, is semi-vascular and grows up to 400 feet tall with the help of the high humidity the clouds trap in, with fruticose "leaves" 90 feet in length not being uncommon. Its lineage was the first of the lichens to become tree-like, but smaller Aliqualignum ramyrtus is among the first woody lichens, shrub-like in form and named after its resemblance to myrtle. It uses its exposed, spore-producing apothecia as leaves for photosynthesis instead of its full stem. Although Psilogrodendron latacephalo is much taller than Aliqualignum ramyrtus and takes access to the sunlight above more quickly, it is rather short-lived for its size and lives no longer than a few-hundred years, most often falling victim to fungi-returned-decomposers, parasitic primary consumers, or strong winds that topple over dying individuals. Aliqualignum ramyrtus' strong, rigid outer layers provide it greater protection against the outside elements, and Aliqualignum and its woody relatives will eventually replace the tall Psilogrodendron currently characteristic of the landscape, growing tree-like in form as the Psilogrodendron once did but better at staving off the hazards that problem trees.