From the weathered stones of Nishsystir to the fresh stone of Mossfellheim, swashes of bright green hug the sides of the islands. These are mangroves, teeming with life. Protectors of the land and a crucial home to many aquatic animals, the mangroves consist of many different species of plants. None however, are as curious as the sailtree.

The sailtree is a stout, salt-tolerant member of the Asteraceae family. Upon first glance, the sailtree looks like a member of the Avicennia genus. It also has many features identical to mainland mangrove trees such as an ability to live an anaerobic conditions, salt secretion, and dendritic prop roots. However, a distinguishing feature of the sailtree from its mainland counterparts is its large yellow flower and the distinctive sail-propelled seed pods.

Throughout the year, the sailtree produces rubbery vines which dangle low to the water. At the tips of these vines a large, orange bulb the size of a honeydew will sprout. The bulb is surrounded by several yellow florets, giving it the appearance of a yellow crown. After fertilization, the florets fall off and the bulb matures into a hard woody capsule. At this point, the vine begins to atrophy. Through the action of wind or waves, the capsule will easily fall into the water below.

As it plops into the salty water, the capsule rights itself with a small woody nub positioned dorsally. In insides of the capsule contains the fertilized seeds of the sailtree, and much like a coconut it protects them from the salinity and movement of the ocean. Unlike a coconut, the capsule contains a unique trick of evolution. Within a few hours of landing in the water, the hard nub of the capsule erupts into a strong mast with a matrix of white fibers. The fibers quickly unfurl into a sheet. The sheets eventually coalesce into a sail with the use of sticky, waterproof secretions produced by sailtree capsules. Fully unfurled sails easily reach surface areas of six to eight square feet.

With the sail prepared, the capsule has finally transformed into its aquatic form - the sailseed. Using both wind and ocean currents, sailseeds are able to quickly disperse from their parent tree. Individual variations on capsule shape, mast size, and sail orientation can result in varied paths for sailseeds. Unfortunately, sailseeds do not have an effective covering like many other aquatic plants, and the outer capsule will begin to wear down within a week. This limitation has largely resulted in sailseeds being limited to the Mossfell archipelago, aside from some vagrant specimens found in Azores. Upon reaching favorable conditions, the sailseed sheds its sail and begins anchoring its thick taproot into sediment. A sailtree with then take anywhere from 5-10 years to mature.

The sailtree is a member of the genus Yggdrasil. Members of this genus are quite ubiquitous on the Mossfell islands, and are known for their thick taproots and unique seed-dispersal methods. Thought to have been one of the earliest arrivals to the Mossfell archipelago (perhaps even up to 18mya), the primordial ancestors of the sailtree were likely among the first herbaceous plants to adapt to a flooded and salty home. Genotypic analysis has recently identified dandelions as the closest relative. Much like the scalesia forests which dot the Galapagos islands, sailtrees have adapted from a small ancestor into an impressive and iconic feature of the Mossfells.

The earliest accounts of Norse explorers mention the sailtrees in great detail. During the Mossfell-Norse Golden Age, sailtree seeds were described as "friendly vessels [which] bring us the hope of land near by. [Their] sails beckon us back to our home". In another account, the Thorkyr Runestone credits sailseeds for leading a crew through the treacherous Mossfellheim channel. 

Following the collapse of the Mossfell Norse, Viardrmen culture gave a more spiritual take on the sailtree. Viardrmen consider the sailseed to the unitive spirit of land and sea, and have many myths which detail the arrival of the sailseed with the arrival of their ancestors (the Norse and Algonquin peoples) to the island.

During the U.S. antebellum, the sailseed became an icon of hope and deliverance for the enslaved population on the islands. Often forced to work grueling labor on sugar and cotton plantations, enslaved individuals spun tales and songs of the sailtree and its seeds as vehicles to escape their enslavement. The sailtree also became a symbol of defiance against their captors, as fresh sailseed fibers could be mixed into cotton before they hardened. After hardening, the mixed cotton would be impossible to process conventionally in a cotton gin.

Currently, sailtree mangroves are in decline around many of the urban and industrial centers of the Mossfells. The destruction of mangrove biomes has resulted in greater erosion and costal damage throughout the archipelago. Severe flooding produced by Hurricane Gaston in 2004 led the cities of Canterbury and Fort Sherman to initiate mangrove preservation initiatives along threatened coastline, such as the protection of vulnerable coastal areas from future development. The diminutive isles of Nishsystir is particularly dependent on the presence of the sailtree mangroves to prevent rapid erosion of the little remaining arable land. Models predict that with increased hurricane activity in the mid-Atlantic, the removal of only 20% of the remaining mangroves surrounding Nishsystir may result in complete erosion of the tiny isles within 200 years. It remains to be seen if preservation initiatives are enough to protect the islands from the next "Big One".