Plants, despite being rooted to a fixed location, have managed to cloak the planet with a protective, nurturing and nourishing layer of vegetation that extends to the fringe of the polar ice caps.
Irrespective of which continent I have travelled on, the floral Kingdom has never ceased to amaze me in how plant evolution has developed dispersal strategies which employ the full spectrum of the natural world to distribute their seeds.
Winged seeds for wind dispersal, fleshy fruit for bird and bat dispersal, ‘sticky’ seeds to cling to bird bills, barbed seeds dispersed by furry quadrupeds. Even exploding seed pods and waterproof capsules fit into the tome of Zen and the Art of vegetative Propagation. All seed designs are strategic mechanisms to perpetuate the gradual migration of a species as it follows the constantly shifting thermocline of global warming.
Without a doubt the greater diversity of seed dispersal strategies increases in complexity and variation closer to the lower latitudes, a direct correlation to the increased speciation forged by temperature and disease.
Nowhere is this more apparent than in the Cape Floral Kingdom of South Africa, where a mere hectare of Fynbos contains more plant species than the entire United Kingdom. In the postage stamp of the Garden Route, a few hectares of Afromontane Forest hosts more tree species than the full extent of Canada.
It is in this overwhelming floral diversity that seed dispersal strategies approach the complexity of expedition campaigns.
From Ficus spp which adjust their fruit temperatures to maintain a population balance between species specific wasps and parasitic nematodes to ensure sufficient ripe fruit to reward birds and bats for dispersing their seeds.
Or the Podocarpus spp which regulate the palatability of their fruit to control the foraging time of birds, such as the Knysna Turaco. By doing so the Podocarpus forces birds to have frequent foraging forays over an extended period of time, thereby ensuring a more comprehensive dispersal of their seed.
Another ingenious strategy is displayed by Pelargonium spp. Their seeds, sculpted by evolution, are nothing short of an engineering marvel. The seed is attached to a tightly spiralling tail, the remnant of the style which elongated after fertilisation. Composed of two layers of structural material with different factors of moisture retention and absorption, style spiral as it dries as the seed matures. As it spiral, fine hair like fibres splay out, forming a tuft.
With the first puff of wind, the seed flies off, eventually landing to remain dormant in anticipation of the next amazing act of engineering. During the next rain the spiral rehydrates causing it to unwind, slowly drilling the seed head through the humus layer, into perfect conditions for germination.
It is in the midst of the sheer volume of seed dispersal strategies, it was with delight that this week we witnessed a subtle variation on the pelargonium spiral. Walking along an exposed game trail through the Fynbos, I noticed a column of ants carrying seeds with a spiralled tail. Close inspection revealed that the spiral lacked the usual fine tuft of fibres.
I concluded that, prior to transporting the seeds to their nest, the ants must have stripped the tuft off, possibly a precaution to being carried away in a breeze and to reduce any snags during their walk.
In reality we had to walk a further 50m before discovering that it was indeed the plants which had evolved a seed whose tail was indeed without a tuft. For there in the middle of the path was a Pelargonium with ripe seeds, each one sporting a naked spiraled tail.
Growing in hard, sun baked sand, this species most likely required a different method of seed dispersal, and like many other Fynbos species, relied on ants to assist in dispersal and germination, a requirement most likely assisted by the naked spiral.
Now patience and luck will reveal the next stage that leads to germination after the ants store the seeds in there nest. Or is it merely as simple that every now and then a seed is dropped into a crack in the path, inert till the next rain?