The Everwood tree (Archedendros sempervivens) is an extinct plant once found throughout Greater Equestria. It was able to overcome hydraulic limitations on tree height by absorbing rainwater through modified leaves. Note that the everwood tree was a broad-leafed flowering evergreen, something that would be quite unusual on Earth. Everwoods were once the dominant tree species of subtropical to temperate climates of Equestria where soil conditions were suitable and it rained with sufficient frequency to allow the plant to absorb water other than through its root system.
The everwood tree can live many thousands of years; dendrochronology (the Everwood has annual growth rings) has shown that the 95th percentile of these trees reached 3.8x10^4 years. The last of its kind, Great Archaeus, had 36,102 annual growth rings in 652 AE, all of which were counted individually by the reclusive savant, Ring Mare, a fellow of the Arcane Helix. (Some years after its death.) The 95th percentile of everwood tree height at death was 252m.
Everwood trees were passively magical, the heartwood containing specialized crystal-producing cells that enhanced the compressive and tensile strength of the wood by establishing favorable low-energy magical resonances with each other. The peripheral tissues, especially pedicles and leaves, do not have mature crystal-producing cells - the immature crystal is smaller, and does not have the appropriate physiomagical properties to establish a stabilizing resonance. Instead, its interaction with the changing ambient magical field causes it to undergo minute vibrations which it dissipates as heat. In this way, the broad leaves of the tree endure freezing temperatures, but the thick trunk does not reach protein-denaturing temperatures by the same mechanism.
Both of these effects, which are powered by ambient magical flux and not by the mundane metabolism of the tree, persist the death of the tree, but because the seasoning of wood affects its dimensions, the precise spacing of the mature crystal-producing cells is disrupted, and seasoned everwood lumber is not much stronger than that of ordinary hardwoods. However, large pieces of everwood lumber have been known to spontaneously combust as the crystal array reverts to producing heat as it did when its crystals were immature. A square everwood timber of 40cm * 40cm or greater in cross-section will destroy itself through violent dry distillation during the seasoning if it is not processed carefully (knowledge of seasoning techniques for everwood is generally lost in the present; 25% of Equestrian Lumberjacks polled believe that it is best seasoned “with rosemary and possibly chives.”) Ancient craftsponies have managed to make some everwood artifacts that retain their terrific strength by replacing the water with a blend of organic waxes; the process and reagents necessary are unknown to modern pony, as, the tree being extinct, there is no pressing need to rediscover them.
Recently, in the time of PRPG3, the species has been restored from total extinction. Nisente, a well-read shadhavar mare, was scavenging in the remnants of the Arcane Helix when she realized from scraps of literature that the tree at its core was extinct in its native dimension. However, she had previously seen that the inhabitants of New Unicornia still had a few living examples in their gardens. Sensing an opportunity, Nisente put together a small party to travel with her to New Unicornia, where she succeeded in acquiring a small hoofful of Everwood seeds. After further travel, she was able to have a portal opened to obtain passage from the Dread Dimensions to Equus, where she offered the seeds for sale to ponies in exchange for her own weight in gold. The ponies paid this gladly, considering it a more than fair price for the miraculous return against all odds of a valuable long-lost species. After careful propagation, a few new groves of Everwood trees have been planted in (among other locations around Equus) the Yore Mountains, at elevations where a suitable cooler cloud forest biome exists for them to thrive.