Black plants are an ancient descendent of early red plants that have survived several extinction events and evolved on a separate path for over a hundred million years. Thus, their form and lifestyle differ greatly from that of their red plant ancestors.
Symbiosis with black algae allowed these plants to grow in locations that are too shady for red plants. Ancestral black plants were not much more than black versions of their red progenitors, but they lacked the ability to produce mobile fruits, opting for rigid seed casings instead. Modern black plants exhibit secondary growth on some groups and a well-developed vascular system (derived from the plicozoan gut) terminating in hair-thin microphylls. These are an outlet for thermoregulation, as black plants are prone to overheating, and are less likely to be shed in high winds than true leaves. Despite their name, not all black plants are fully black. Some of their ancestral red coloring shows through in areas not exposed to any sun, or areas exposed to too much direct sunlight. When cut, they bleed pink. A few species have secondarily lost their symbiotic black algae completely. Black plants absorb light in the red and infrared, while red plants absorb light in the infrared and (to a lesser extent) green.
While not exactly repersentative of black plants, crassimorphs contain variations on structures present in most members of the clade. The heart, an ancestral trait, is maintained in most species. Their height requires a mechanism to pump blood throughout the body. Only unifoliates lack a heart: this limits their height and relegates them to a grass-like niche. Other plants, like some of the tallest trees, have multiple hearts.
The fat storage and deposition organs are unique to black plants. Red plants store fat in adipose tissue. Black plants store fat in a cavity filled with keratin spurs that provide strength and surface area to the organ. There is no tissue here, only fat solids and a steady drip of emulsification agents. These agents, similar to bile, are secreted by a blood filtration organ located above the cavity. This allows the fat to reenter the bloodstream in a safe form when needed by the rest of the plant.
Reproduction varies widely between clades and even species. In this example, the fruits develop separately from the pollination organ system (the “flower” of sorts) and are connected by a portal vein which carries pollen to unfertilized seeds before returning to the heart. Parasites and pathogens can enter the plant through this route. Crucial components of the immune system are often concentrated along this vein.
A second vascular system, more similar to that of Earth plants, makes up the cambium of heavy-bodied black plants. Plants obtain and transport exogenous nutrients and water using this system. The cardiovascular system is limited to transport of oxygen and metabolic products. The two systems are kept separate to protect the plant from disease.
Pennifoliates – This group includes crow’s feet and other tall, spindly plants. Having not evolved secondary growth yet, they are flexible and can sway freely in the wind without snapping. Their stems always terminate in a fixed number of feathered branches. They reproduce with a pollen-producing anther at the base of the plant and a seed-producing organ just above it. To avoid self-pollination, these structures ripen at different times.
Unifoliates – These are similar to pennifoliates but the microphylls grow directly off the stem in two opposite rows. In a strange case of convergence, the microphylls lock together with barbs remarkably similar to those on a bird’s flight feathers. Unifoliate fields are probably the closest thing Ilion has to grasslands.
Pterosperms – The seeds of pterosperms are the only organism capable of powered flight. They are unleashed in large numbers so that some will inevitably land in the “catcher’s mitt” anthers that grow out of the base of other trees. In the most advanced species, these seeds can even take off and germinate elsewhere. In other species, the mitt builds up internal gas pressure until it explodes, sending its contents flying. Otherwise, they must rely on the wind or animals for dispersal.
Caecosperms – This group includes the cliffhangers and other small trees. Caecosperms have a shaggy coat that covers all sun-facing parts of the plant. The seeds of caecosperms are hidden in a blind pouch. At the entrance lies an anther that closes like a trap door when an animal crawls inside to drink the nectar. When the animal crawls out, it brushes past the anther and carries the pollen to other plants.
Crassimorphs – Crassimorphs are caecosperms that have lost their branches. Instead, they grow a thick trunk that is almost spherical in some species and cactus-like in others. Crassimorphs include the blackbushes and other related species. Like their cousins, crassimorphs house their male and female reproductive larvae in cavities inside the trunk. They rely on animals for pollination and animals or wind for dispersal.
The dancing pitcher-catcher, above, is typical among Pandaros savanna trees in its willingness to bend in the wind. The wind is strong here, but not so heavy as to encourage the growth of stouter species like the Wulff’s pitcher-catcher of the south. The dancing pitcher-catcher bears fruit continuously but produces seeds only intermittently. When a tree goes into seed, it sends out pheromones that suppress the seed production of trees downwind so they will focus their energies on fruiting instead. Fertilized fruits turn from red to gold and shed their thorns so they can be eaten by frugivores such as the hognose thrax.
Ilion’s early explorers were surprised to find that the life there did not fit into neat boxes like “plant,” “animal,” and “vertebrate.” They found insectoid lifeforms – but they were not animals. They were the flying seeds of pterosperm black plants. Some of the trees appeared to be infested with wood fungus – but it was not fungus. The structures belonged to the tree; their purpose was to attract and fertilize the flying seeds, then develop into a fruit. Ilion’s higher gravity and lower oxygen levels limited the evolution of flight among animals. Here, plants rule the skies. Pterosperm seeds are short-lived and single-minded. Their goal is to disperse and find a pollen pad or pitcher of their own species while avoiding predation.
All flying seeds have four limbs, a tail, and a head. The head contains the main sensory organs for sight, balance, and olfaction. It also contains the opening through which pollen is ingested. The limbs are divided into upper and lower. The upper limbs are wings. The lower limbs can be wings, feet, halteres, or vestigial remnants. Some seeds also possess a caudal fin for stabilization during flight. The function of the tail varies from species to species. For some, it is a balancing organ; for others, a grasping appendage. While attached to the parent tree, the seed is fed through the tail and in some cases the tail’s function as a feeding proboscis persists beyond its connection to the tree. Heterotrophic seeds pierce plants to drink from their blood vessels. These seeds tend to survive longer and may one day spawn an animal lineage of their own.
The bugle-shaped growths are the tiny fruting bodies of the graphite tree, which is named for the dry, slippery texture of its bark along with its silvery sheen. The tree is dessication resistant and well suited to the desert environment it lives in, as are the aquaphores growing at the roots.
The brittle tree grows on the coastal shrublands of East Pandaros. The tree grows rapidly to a height of 30 meters before splintering, rapidly again, under the strong easterly winds. Other trees in the area have no trouble staying upright, so what gives?
For the brittle tree, falling is just another phase in its life cycle. The tree produces flying seeds while growing, but unlike other pterosperm trees, no pollen pads or other receptacles can be found on the base of the trunk. These erupt only from the stump of a felled tree. Seeds travel long distances to these outgrowths to be fertilized before taking off again in search of a place to take root. To a biologist unfamiliar with the workings of Ilion’s life, this might look like an interaction between multiple species: a dying tree, a fungus, and an insectoid pollinator, perhaps.