Hmmm, let's give this a go.
The Dendrani
In the middle of the jungle there is a city that appears to be built of giant, still-living trees. The city is home to plant-creatures having squid-like bodies with tentacles like vines that contort their forms into various shapes. They often weave their limbs into arms and legs to appear humanoid if they need to make contact with others. The trees hold up stone boulders and logs to help form the "buildings" of the city as though the trees grew around them. Of course, this isn't the case. The trees simply picked them up. This is a city of the Dendrani, and what most people don't understand is that those trees are as much Dendrani as the green-vine-squid things they occasionally have dealings with.
The Dendrani have a strange life-cycle. They are somewhat like jellyfish, producing two major forms of life - first polyps and then medusae. The living trees are the polyp stage and the smaller, more mobile entities that can assume humanoid form are the medusae. According to their own internal physiology and the cycles of nature, mature medusae sprout large blossoms on their heads when they are ready to reproduce. They gather, typically on the night of a full moon and release their pollen into the air. Some will be successfully pollinated and bear fruit - or perhaps eggs would be a more appropriate term? They plant/lay these fruit/eggs in fertile, warm soil and in time young polyps sprout. The polyps look very much like a normal tree, and do indeed take nutrients from the soil and photosynthesize.
But once they reach about shoulder height to a human they reveal a different nature, becoming mobile and even predatory. They catch and kill insects and small vertebrates that aren't fast enough before consuming the kill through their roots, not requiring any tending to from their parent and indeed having no relationship with them. Once the polyps grow large enough - a process that can take decades depending on the nutrition and environment the polyp has access to - they produce a single medusa-stage individual from their trunks. The polyp then becomes the medusa's guardian, allowing them to return to the trunk as a joey does to it's mother's pouch. Even once mature, the medusa can return to the polyp to enter into an indefinite period of stasis should it need to. The polyp never stops growing and once the medusa is mature and can hunt or forage for themselves they also bring back fertilizer for their polyp, accelerating this growth to some degree.
In time, the polyps grow to be so large, strong and slow that they enter long-term sedentary state. This is usually by merging into a "city" of other polyps where many Dendrani gather. The polyp does not sleep, instead remaining aware of its environs, but it can become non-responsive and should it be in this state for too long it can take considerable time to get moving, as though awakening from a coma. Both the polyp and the medusa do not die of old age, though they become deeply lethargic about five hundred years or so after reaching maturity and typically the polyp chooses to enter a state of prolonged hibernation in their polyp which remains unresponsive during this period, ending only when called by others of their kind in times of need. Should the polyp die before this, the medusa will likely die when it would have entered into this stasis - though exactly why is unclear. Should the medusa die, the polyp will still technically live but completely cease to respond, essentially shutting down until it is indistinguishable from a tree.
The polyp and medusa do not consider themselves distinct individuals, but rather two separate bodies of the same person. While the medusa has most of the brain-power, both of them can see, hear, feel and remember. Indeed, the polyp can very efficiently store memories for the medusa, acting as a kind of personal library of lived experiences. The polyp is far less social and whether or not most even can communicate with others is an open question. The key exception being the communication between a polyp and their medusa. As long as they are within a hundred feet or so, a polyp and their medusa can communicate quickly and soundlessly. It is not known if this is a psychic connection or communication based on pheromone signals or something else. The result is that medusa frequently return to their polyp to catch up on the days events and most still choose to sleep inside their polyps trunk to share dreams with the sleepless entities. The hollow in the polyp can grow to a significant enough size that it can be furnished as any home would be.
The medusa can use their polyp to spy on those who don't understand that with Dendrani, the trees have eyes and ears. They can also call on their polyp for aid if they are under threat. The sight of an entire Dendrani city disassembling itself and chasing after would-be raiders is an awesome and terrifying thing. Most often, the polyps of mature medusa can be seen moving when used as transportation. The Dendrani have no need of wagons or carriages when polyps serve that purpose just as well.
Dendrani are an extremely reclusive and secretive people. It is unknown how many there are nor how large their cities can grow deep within the uncharted jungles. There are reports of some Dendrani being found in far away places, hiding in plain sight in woods or even by human villages by taking the place of other trees - though it is not clear how many of these reports are indeed Dendrani or a case of mistaken identity with dryads, awakened trees or treants. It is possible these Dendrani are simply curious or have a touch of wanderlust, having simply opted for a change of scenery before entering into a long stasis, but it is hard not to draw more sinister conclusions. There are some who theorize that the Dendrani were once a widespread and powerful civilization that has since fallen and on account of their unique "architecture", there are no obviously visible signs of such a society. It's possible these Dendrani found in strange places are engaging in pilgrimages to ancient holy sites or watching over something they did leave behind that humanoids don't recognize as the work of an ancient culture. For all we know, that forest may in fact be a Dendrani burial ground, where the oldest trees are in fact polyps who lost their medusae. They could also be watching and learning in preparation for their return to ascendancy.
What little is known of Dendrani culture is entirely alien. They do not form any relationships with their offspring, the infant polyps instead being left to wander in the wilderness. If a polyp or medusa finds another Dendrani or even a city, they are driven away until they reach maturity. They maintain the capacity to quickly learn new skills and languages (like humanoid infants do) right throughout their lives and so when they are ready to integrate into society they do so quickly. Their notion of kinship seems to be more about nested levels of friendship between the medusae. There are acquaintances one has little attachment to and friends one would die for - though this does not necessarily correlate with the medusae they spend most of their time with, which seems to be a different dimension to their notion of relations. It seems they distinguish between important friends (who one values very highly) and good friends (whose company one voluntarily enjoys often). There are terms for one relates to another through this complicated network just as humans have terms for aunts, uncles and second cousins once removed. They also seem to place some value in the relationships between polyps though this seems to simply be that polyps share a space as neighbors or prefer similar soils or similar animals for consumption as fertilizers.
The Dendrani society within a given city seems to be organized around what one might call guilds. A medusa seeking to pursue a particular skill becomes an apprentice and is gradually recognized within the guild as they prove their merit and provide their services. How one is treated in wider society depends on how that guild is treated. These guilds are not consistent across cities and each city may not even have corresponding guilds fulfilling a similar role. A medusa who is a lowly apprentice in one village may be treated as virtual royalty in another and this is not considered at odds in any way, even if they guilds in either city pursue the same skill. A medusa's polyp in no way reflects their chosen guild nor their rank. In fact it is considered extremely rude to discuss a medusa's profession within earshot of their polyp, as though that is an aspect of the polyp-medusa conglomeration specifically belongs to the medusa. Some of the most common skills one finds in Dendrani guilds are of a magical nature. Most medusae do have some measure of skill with magic.
Dendrani do not often work with fire - as might be expected considering how flammable the polyps' wood is. They thus do not often have worked metal or ceramic. Instead they work with textiles, animal products like bone and horn as well as a not-yet-understood method for creating extremely strong and potentially sharp petrified wood. Weapons are typically made of this wood and are usually piercing weapons with barbs that tear into flesh if one tries to remove it by pulling it out. They preserve the petals of the blossoms from their heads after they plant/lay their fruit/eggs. These are then used as decorative pieces alongside other plant- and animal-based materials to make art. Unlike many other cultures which might make a painting or stature to be passively admired, the Dendrani create art that is to be moved through, interacted with and ultimately destroyed due to wear and tear. Considering their life spans and ability to store information, they do not concern themselves with maintaining or curating such works.