The Lahit were a non-humanoid arboreal species native to Flyspeck (1212 Muscae IV), coexisting on the planet with the Ornae. In the late 2260s, approx. 20 million Lahit lived on Flyspeck. They formed hive economies and moved across the surface as colonies. Lahit were also welcome to live among the Ornae in their makeshift settlements. Following first contact, a treaty was signed with the Federation. The Lahit and Ornae intended to join the Federation. (TOS novel: Doctor's Orders) They could also exist as individuals. By the late 24th century at least one Lahit served in Starfleet. (ST - The Fall novel: The Poisoned Chalice)
A Lahit could consist of a single tree or a small forest connected by a hive mind. Their numerous eyes appeared like berries on first glance. The Lahit were capable of locomotion by uprooting and re-rooting in the ground, leaving trails as they moved along. (TOS novel: Doctor's Orders) Leaves and vines served as their appendages. Lahit had no sexes. (ST - The Fall novel: The Poisoned Chalice)
The Lahit and Ornae evolved from a common ancestor. By the late mid-23rd century, their were 20 million Lahit on Flyspeck after their numbers were violently diminished by Orion pirates raiding the planet.
At some point, an ;At settled on the planet to protect them but was ineffectual against the Orions.
In the late 2260s, a Federation survey expedition made first contact with the Lahit, Ornae and ;At. The survey failed to gain sufficient information on the Lahit language to program the universal translator. When the USS Enterprise arrived to study Muscae IV and its inhabitants in detail, communications officer Nyota Uhura and linguist Janíce Kerasus enabled the UT to master the Ornae and Lahit languages. Soon after a Klingon ship, the IKV Ekkava arrived and first contact with the Klingon Empire took place. In a joint effort, the Klingons and the Enterprise defended the planet against the Orion, crippling the pirate vessel.
Master, the ;At guarding the planet, was convinced that Federation membership would enrich the Lahit and Ornae. Subsequently, the Lahit and Ornae agreed to a treaty with the Federation, negotiated by James T. Kirk, and planned to apply for membership. (TOS novel: Doctor's Orders)
In 2385, Doctor Rssuu served as chief medical officer aboard USS Lionheart. He was firmly rooted in sickbay. His vines extended into every part of sickbay and were his appendages to treat patients with. (ST - The Fall novel: The Poisoned Chalice)