One to Three
While Amorphophallus plants on Earth have single leaves with three main branches, some plants on Aroidia have three separate growing points that fuse to become one plant. Triklados is the Aroidian genus noted for this three-branched structure, but another closely related genus, Trispadia, has the distinction of having both a unique and complex life cycle and the most gorgeous inflorescence of all I've imagined on Aroidia.
At right is shown the tripartite inflorescence of Trispadia speciosissima, produced by a plant that is actually a fusion of three plants! While Triklados plants have three growing points that eventually fuse to become one, the three are present on a single tuberous underground organ. Thus they are actually more like three buds on one plant. By contrast, Trispadia starts with three distinct and separate plants that come together and fuse to become one. Trispadia is what I call a heterogenetic plant, which means that each sexually mature specimen has three different pairs of chromosome strands. One pair of chromosome strands comes from each of the three juvenile plants that, together, make up the single mature and blooming Trispadia plant.
On Earth, heterogenesis refers to the appearance of mutations in a population. In terms of the life cycle of Trispadia on Aroidia, heterogenesis is the process whereby seedlings of Trispadia mutate progressively until enough differences have accumulated to enable the tri-fusion process and subsequent blooming. You see, simply germinating and growing semmules of Trispadia will not result in a blooming specimen. Such seedlings may grow for years and never produce a bloom. They will not even develop the characteristic mature growth habit of a blooming specimen of Trispadia! True maturation cannot take place until enough systemic mutations have occurred within each seedling in a population. These mutations must be constructive, or the seedling will self-terminate. This process enables Trispadia to exhibit deliberate, real-time evolution within just a few generations.
Three to One
Trispadia seedlings begin by growing into plants with upright, fern-like fronds. This growth phase is what could be referred to as the pseudo-gametophyte phase, and is the phase in which the diversifying mutations occur. Once the required amount of mutation is evident, the growth pattern of the seedlings changes abruptly. In the pre-fusion phase that follows, fronds begin recurving to a horizontal orientation. Simultaneously with this, underground rhizomes begin to form, seeking out and attempting fusion with nearby seedlings. Sexual reproduction becomes possible only after three plants of appropriately distinct genetic constitution have fused successfully.
Once this underground fusion is complete, the recurvature of the fronds alters so that all fronds of the fused plant are pointing inward. In so doing, they form a sort of canopy under which the future inflorescence will develop. Once the fronds are in position, further growth takes place underground as the creeping rhizomes of the three contributing seedlings, now fused, form a central underground structure which will yield the bloom buds, or primordia. These bloom primordia then begin growing towards the surface, emerging together to form the complete tripartite inflorescence. The cells of each of the three contributing plants differentiate into specific parts of the inflorescence, with the eventual result being the spectacular bloom having three spathes and three spadices.
Pollination of the spadices of the inflorescence is facilitated by tiny, flea-like pollenoids that "hop" from one spadix to the other. Inbreeding is not taking place here because each of the three contributing plants, along with their respective portions of the tripartite inflorescence, are genetically distinct and diverse. Consequently, Trispadia pollenoids never need to venture beyond the three spadices of the inflorescence from which they emerged.
Pollinated Trispadia infructescences form small seeds in copious quantities. This insures that enough constructive mutants will develop and survive to produce the next generation. After fruiting, the parent plant dies off. The seeds always land near the parent plant, so Trispadia are found growing in colonies. Since most of the seedlings do not survive the mutation cycle, these colonies never become overpopulated.
This idea of genetic fusion brought back to mind the one Aroidian plant which has five sexes, truly the most complex life cycle of any living thing there. So my next adventure was to seek out and study this most astonishing plant, known as The Keeper of the Gate. . .
Picture credit: LariAnn Garner, Aroidia Research
(Continued in Part XI: The Keeper of the Gate)