Aroids of the imagination XI - The Keeper of the Gate
From five comes One
Remembering that all life on Aroidia functioned as a global organism in spite of the diversity, i had to wonder what served as the "nervous system" or communication infrastructure for all of the other "organs" there. As my visionary imagination would have it, I was moving steadily in the direction of the north pole. I knew that the poles were the only two places on Aroidia where the plants remained undamaged by the annual storm activity. The inevitable conclusion was that if any site on the planet could serve as the seat of global communication, the poles were the most likely candidates. Somehow, recognizing that Pinnatidendron plants were so ubiquitous, I had a sneaking suspicion that they served another purpose besides being the primary contributors to the infrastructure of biological archipelagos. I was not wrong in this and the lack of inflorescences on Pinnatidendron turned out to be a clue. The Pinnate Tree was also one of the five gamete contributors to what I discovered was known as the Keeper of the Gate, Aroidendron heterophyllum.
Broadcasting on all bands
When my imagination brought me to the north pole on Aroidia, I had my first glimpse of this phenomenally gargantuan plant. To say it is large is to display a gift for understatement, as this aroid tree is over 3000 feet tall (see picture, below left)! At first the sight of Aroidendron was confusing, as it seemed to have several different kinds of leaves and complex, compound inflorescences. I missed the inflorescences initially because their spathes were sky blue, blending almost perfectly with the Aroidian sky, and the spadices were like puffs the color of cumulus clouds. I noticed another kind of branched structure on some limbs as something I couldn't identify. It was neither leaf, stem, nor inflorescence, but almost intermediate between them all. Oddly, it actually resembled a huge vegetative antenna! On further reflection I envisaged that this new structure actually did serve the purpose of an antenna, broadcasting radio frequency radiation planetwide.
But what was being broadcast, and what was supposed to answer this message? One of the answers was not to be found in pollenoids, but in gametes, haploid packets containing DNA strands coming from five different obligate gametophytes on Aroidia. These were plants that never grew in a sporophyte phase, but rather only as gametophytes and only to produce the gametes that could join with the others to produce a semmule for Aroidendron. I remembered that I had already encountered one of these unusual plants; it was Lanceolum bicorrugatum. Another was Pinnatidendron, and that meant I had three others left to discover. This was true because Aroidendron required five different gametes in order to produce a semmule that could grow into another Aroidendron plant. Essentially, Aroidendron had five sexes!
I wondered what would happen if less than five gametes "showed up" for fertilization. The answer came quickly; ten possible gamete pair combinations existed. For each of these ten, semmules giving rise to distinctly different plants would be produced! This was the true source for new Pinnatidendron plants, as even though the Bead Trees had appeared to me at first to be the reproductive phase of Pinnatidendron, they never produced Pinnatidendron semmules. Instead, the semmules of Bead Trees grew into more Bead Trees. The relationship of these two was that the Bead Tree derived its ability to reproduce from Pinnatidendron but not for the purpose of reproducing Pinnatidendron itself! In return, the Bead Tree enabled Pinnatidendron to produce one of the five vital gamete types to send to Aroidendron.
Thus I found that only a combination of each of the five different gametes together could yield a semmule that would grow into an Aroidendron plant. The mystery here was why I never found evidence that Aroidendron semmules had germinated and grown in any places other than the north or south poles. The possibility was certainly a credible one, as semmules could be dispersed to germinate anywhere, even if the resulting trees did not survive the storm season. Part of the answer came in realizing the primary purpose served by Aroidendron on Aroidia. That purpose was to act as a two-way transmitting/receiving station for the global organism, using the tall Pinnatidendron plants as repeater stations for all planetary communications. This network exemplified the advanced technology that I had missed completely. It was the way and means for all of the apparently separate organisms on Aroidia to communicate one with another and thus to function as one planetwide organism. The lifeforms themselves had been engineered deliberately to provide this global communications network!
Blooms that are not blooms
Aroidendron inflorescences were not what they seemed to be at first glance either. What had struck me as spathes and spadices were actually parts of what I had to call a super-inflorescence. The structure was much like an inflorescence on some palm trees found on Earth, but instead of small inconspicuous florets, each Aroidendron floret appeared as a full-sized spathe with spadix. Unlike aroid spadices, these did not produce pollen or ovules but rather acted as receptors for the incoming gametes. Any combination of different gametes other than five would have to be a pair in order to yield a semmule; triploids and tetraploids consisting of three or four different gametes would not yield fertile semmules. To prevent such combinations, Aroidendron florets undergo physiological changes for each different gamete they receive. Zygote formation is halted on the arrival of a third and fourth different gamete and can only resume when the fifth distinct gamete arrives. If the fifth gamete does not arrive within the receptive or fertile period, the odd gamete out (if any) is discarded and the remaining pair(s) develop into semmules. These semmules will not produce Aroidendron plants, but rather one of the five obligate gametophyte plants. Multiple gametes of one type do not elicit any fertilization response from the floret.
Going down, down, down . . .
A successful union of the five different gametes does not result in the production of a semmule-containing fruit high up in the tree. In a process more congruent with the unearthly nature of many biological processes on Aroidia, the newly formed di-pentaploid zygote germinates at the floret and grows a tube that progresses down the stem of the inflorescence, down through the branch system, and further down the incredibly tall trunk of the tree. As the tube advances downward, the trailing portion is digested away, resulting in what appears as a capsule containing a large protosemmule cell mass moving ever downward towards the ground. Once this protosemmule reaches ground level, it continues growing below the surface, into the underground structure of the Aroidendron tree. This underground structure resembles a very thick lignified taproot that descends nearly 1000 feet towards the ocean floor. On reaching the bottom of this structure, the protosemmule swells with growth to form the semmule proper. This monster, the size of a wrecking ball, packs enough stored nutrients to last for thousands of years if necessary.
Once three of these gigantic semmules have formed successfully, Aroidendron produces only those semmules that will grow into the obligate gametophytes.
All that remained for me to find out was how the gametes made their way from distant archipelagos to the receptive inflorescences on the Keeper of the Gate. Not having observed any pollenoid-like motile vehicles to transport them, I was temporarily at a loss to understand how they could accomplish the journey. The answer was in the motile symbiotic partner of Pinnatidendron, the humanoid-like Aroidians. Being the gametophyte phase of their own species, no other entity was more appropriate for collecting and transporting the five gametes to Aroidendron. I knew that Pinnatidendron plants had specialized ridges along the rachis on the underside of the fronds. I had seen the Aroidians attach at these ridge areas, but only now did I realize that they collected Pinnatidendron gametes from gametangia found there. On the way to Aroidendron, the Aroidians stopped at each of the four other obligate gametophytes to gather the remaining gametes.
Many more wonders remained for me to explore, so I took my leave of the Keeper of the Gate and proceeded to make a quick inventory of genera and species not yet described. . .
Picture credit: LariAnn Garner, Aroidia Research
(Continued in Part XII: Snake Tongues, Right-Handers, and other Wonders)