D&D meets Veggie Tales...

[Admiral Squish]

With respect to the cultural elements, one crucial thing to think about is resource allocation. The major resources humans compete for are food and water, which is to say land for agriculture or pasture, and then rivers. The major resource plants would compete for is sunlight. What this would imply is that taller plants would immediately have shorter plants at their mercy. I can imagine, if they were sentient, a serf-lord relation developing between treant-type creatures and bush-sized creatures. The treants would protect the bushes and provide them with a place to photosynthesize, and in return the bushes would serve them and be beholden to them.

Carnivorous plants would have to have some sort of source of food. Do they eat smaller plants? That would cause photosynthesizers to most likely band together for common protection. As they are mobile, that would mean that all photosynthesizers would be able to relocate into safer places, which would form the basis of towns, where, because of space concerns, they would be even more beholden to the tallest creatures in the area.

Also, this would imply that "forests" are relatively homogenous. You don't have tendriculouses mixing with the treants, because in the absence of rodents and red meat, who is the tendriculous going to attack?

If these towns become real political entities, one must consider their relation to one another. Because photosynthesizers make their own food, they would never really need to trade for anything, nor would they make war against each other (except maybe rivaling for a particularly sunny and safe spot). These communities would, then, be incredibly isolated, perhaps not even being aware of the existence of any other, thinking that perhaps nothing exists except for their forest and surrounding wastes of carnivores.

Also, if every creature on the world is plant-based, there would be no life whatsoever outside of the tropic zone or so, because of the onset of winter outside those zones. Or else everyone in every town dies every year and then wakes up six months later. Might be interesting role-playing that.

Finally, don't expect any of these communities to be at all technologically advanced. Humans only got the chance to invent things like fire (note: fire here means burning the dead. Always.) because we needed to hunt to survive. All plants need to do is hang out in the sun for a while and they're golden. The only incentive to invent technology would be to defend against carnivores, and, as we've seen with terrestrial animals, most species don't need technology to do that.

Apologies for the block of text. I don't know where the elementals fit in. Anyone else want to field that?

I had some ideas about the elementals. Fire elementrals would be particularly important. They would take the form of nomadic warrior tribes with a semi-religious drive. If the setting was populated by Woodling creatures, they would bne particularly dangerous. They roam the countryside in tribes or armies, or possibly even swarms, burning all vegetation as a natural regulator. They would prevent overgrowth, and re-fertilize the soil as they passed.

This function would be a MAJOR shaping factor of the world. 'towns' and massive stretches of forest would be burned, leaving places for new plants to move in. The soil would be incredibly fertile, making it prime real estate. This could make conflict between plant-cultures, clashing over the finest, competition-free soil.

Water elementals would be something like hippies. Enlightened hippies. Owning nothing, they travel through the waters of the land being very chill. Treating them with disrespect of violence would mean you suddenly find your local aquifer moved.

Air elementals would be practically legends. They never go near the surface, anyway.

Earth elementals would be much like water elementals. However, they would be more useful as allies than water elementals. While you just have to treat waters with respectful distance, actively courting earths as allies would help a 'city', maintaining nutrient-rich soils near the surface and even building walls and defensive structures against the fires.

Fungal creatures would likely be rather rare. They would be treated like holy men of sorts, performing last rights on the deceased to maintain the fertility of the soil. and, of course, continue their existence.

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Now, to respond to your points in turn:

Hmm. I'm not so sure on that. Treants are supposed to be tree-lovers in the highest form. I could see treants as something more racist. beleiving trees are truly the highest form of plant-life, and thus deserve the sunlight. The bushes would be more a repressed and abused minority.

'Carnivorous' plants would be nonexistant, though there would be herbivores that feed on other plants. Some would be mobile grazers that would feed on non-mobile plants, others would be hunters that feed on the grazers. The same woody, vine-like material that makes a grazer plant mobile makes them particularly juicy meals. Really, purely hunter plants would probably be a rarity, likely evolved out of the grazers themselves.

Homogenous forests would likely be a must. Towns would be the next logical step. Large groups of 'grazers' forming protective groups, or mobile 'bush' synthesizers working together to prevent the treant domination. HEck, even tribes of 'hunters' would band together to form packs, in all likelihood. This doesn't even require sentience yet, just mobility.

Towns as political entities seems likely. Likely intelligent hunters would eventually come to an accord with intelligent mobile plants of all sorts, resolving to feed only on the unthinking and, lending their strength against the fires, in exhange for the strength numbers bring against the fires and larger unthinking hunters. If they remained mobile, only entering the towns in times of crisis, they could bring tales of other cities. Or, they could remain as 'outsiders' within individual cities, leaving in the mornings and coming back in the evening with their kills, seeking the shelter of the city against nocturnal fungi hunters. Similarly, mobile fungi, with their meandering lifestyle, would probably be well-traveled as well.

As for the tropic zone, we're working with fantasy physics, here. I can say the whole planet is capable of supporting life year round, if I want. Though having deciduous areas might be interesting, as well.

With the looming threat of fire attacks and fending off treant dominators, we now have motivation for creativity and development in the military sector, which is how most developments are made in the first place. Synths would have nothing to do but think and discuss all day in their collectives. Not sure if that would be enough to counteract their sedentary lifestyles in terms of mental evolution, however.

DOUBLE WALL OF TEXT GO!