New Taigas, Old Rivals

It has been some time since the tundras and taigas of the north were one. North America, Europe, and Asia, though seemingly far away from each other on a map, are fairly close to each other at their polar extremes. This allowed the denizens of the cool north to travel from continent to continent with comparative ease, explaining the ranges of reindeer, pine trees, arctic foxes, and moose, just to name a few. Though the continents are in basically the same position then as now, the uninhabitable cap upon the north pole has expanded dramatically. This has pushed habitable land so far south that the remnants of the global north are irrevocably separated from each other.

A similar situation existed in the Southern Hemisphere with South America, southern Africa, Australia, and New Zealand, but not because they are close to each other, but because they once were. Millions of years before our time, when the warmth of the Jurassic caressed the world and dinosaurs cropped leaves from cycads, the land was collected into two great landmasses, Gondwana and Laurasia. Gondwana was the supercontinent that, broadly speaking, compromised the lands that are to the world's south today. But as the Jurassic passed the supercontinent began to break, and as more periods went by, it tore into pieces which went their separate ways. Each, once in the vicinity of some land that heeded from Laurasia, exchanged organisms with it, inevitably causing some loss of its original inhabitants. As modern times approached, the flora especially yielded more and more to their Laurasian competitors. Fewer still would remain when humans spread all over the world, wielding invasive seeds and scorching fire. But the tale is different now; the plants, at least, will write a different story.

Comparing the two polar areas, the great trees of the north and south at first look much the same, with their needle-leaves and brown cones. This is misleading. Those of the north are perhaps most familiar, compromising the family Pinaceae, including pines, larches, firs, spruces, and hemlocks — basically, any pine-y tree, with their woody cones and often characteristically winged seeds. In contrast, those of ancient Gondwana, collectively called Antarctic flora, consist of plants distantly related to these. They include the podocarps, bearing flattened leaves and highly modified, colorful, berry-like cones with only one seed each. There are also the araucarians, prehistoric-looking trees with such massive cones that they can kill people when they fall. The pine family of the north and the podocarps and araucarians of the south have both barely spread into the opposite hemisphere, showing their tenacity, but the Antarctic flora's story has still largely been one of loss.

This all changed when the world froze. The southern hemisphere has cooled so much, giving surviving podocarps and araucarians huge swaths of land to turn into taigas and montane forests, and they have few to compete with while they do so. They will, however, never reclaim their former glory millions of years past. But this truth holds true for the conifers of the north as well. Split into fractured communities, they can no longer maintain a unified dominance over the northern hemisphere. Instead, they are forced to go their separate ways, to form their own communities in isolation.

In the northerners' case, this allows unique changes to occur where once there was uniformity. In North America, this has already produced a lineage of great potential: The alberones, a group all their own among the pine family.

Alberones are an extremely young clade, looking very much like their parent lineage, the firs, to which they do still technically belong. Firs differ from their relatives in various details, but most prominently their cones stick straight up in the air, not hanging upside-down, and the cones disintegrate, with the woody scales and small, windborne seeds breaking off and leaving only a cob. Alberones do similarly, shedding many seeds each season. Upon close inspection, however, they do so in a fundamentally different way.

Their cones, familiarly, consist of scales winding up in spirals, both clockwise and counterclockwise. Less obviously, their cones have an additional degree of complexity: Each scale does not occur alone, but is always in a group of four. It turns out that only one of these scales grows directly from the cone's central stem. The other four are attached not to the stem, but to that connected scale. When the cone is ripe and disintegrates, the entire group of four falls off the central stem as one piece, too heavy to fly in the wind as the individual seeds once did. Perhaps the wandering lips of a splotched goat moving from shrub to shrub will encounter the item, then pick it up and chew it whole. A smaller seed eater, such as a squirrel —  these animals are now unique to North America —  will instead work the seeds out of their woody encasement.

This structure, called an amphora because of its likeness to the ancient Greek clay vessel, is a key ablerone innovation. This is not only because they are fused together, but because the seeds within have begun to specialize in a novel way. The two seeds on the right and left of the amphora, concealed in the woody scales, are termed the fore seed and hind seed, respectively. These are hard and bitter, unlikely to be eaten, and even if so, unlikely to be chewed thoroughly, so they are ready to sprout into a sapling when dropped or defecated onto the forest floor. The two seeds above and below, however, are truly unique. They are termed sacrificial seeds or trophic seeds, and are large, soft, and fatty. The upper sacrificial seed is visible from the top of the amphora after it has fallen, for it is shielded by the lower scale of the amphora above when developing. This tasty morsel serves to tempt a smaller seed-eating animal to break into the structure. The animal will then destroy the amphora in search of the similar lower trophic seed, dropping the hind and fore seeds in the process if they are not eaten. Larger animals, of course, will more likely eat the amphora whole. The trophic seeds are thus useful in both of these scenarios as a sacrifice: From fertilization to the completion of development, they are intended not to sprout themselves, but to aid the propagation of their two luckier siblings, giving themselves up for their sake. Even if they are lucky enough to fall onto a suitable patch of earth, they are unlikely to grow into a tree. Those that do are botanical marvels.

Trophic seeds represent a completely unique innovation among gymnosperms, comparable to a certain oddity angiosperms have. See, gymnosperm seeds develop in whole from tissues from the mother tree, with only the embryo containing any genetic information from the father tree. The seed coat and the energy store is completely the mother's doing. In contrast, angiosperms have a system called double fertilization, in which one sperm and one ovum produces the embryo, while another sperm from the same father and two cells from the mother combine to produce the endosperm, the energy-rich fuel store that defines much of the seed's shape. This gives the father one-third control of this major seed component, giving his genes some say on how the seed develops. For example, it is more advantageous for the father for the seed to have a larger fuel store than it is for the mother, since it is her energy being used to do so, not his. He would also prefer that the seed travels further away than the mother does, since a competitor releasing pollen affects him more negatively than her. it is possible that this helped bring about some of the variation seen in angiosperms, from beans to cacti to dandelions to coconut trees.

The humble alberone, little changed outwardly from its ancestors, is poised for an analogous path. In its case, the father has control of not one third of a major part of the seed, but nearly one half of what is effectively one seed body. It will take time, but time they have, working their way down the American Cordillera, that chain of mountains serving as the continents' spine. The "pines" of North America will be strange indeed.