B'Elanna Torres crash landed the Delta Flyer on a Class L planet in 2376 and was stranded there for several days but Harry Kim finally showed up with the part she needed to contact USS Voyager again. This planet appeared somewhat atypical of a Class L planet as it contained at least one region that supported lush vegetation and even a pre-warp civilization known as Kelis' species. It also produced rain and contained several landmasses and oceans or seas. Little was seen of the planet's surface, so perhaps the remainder of the planet was far less hospitable and more standard for a Class L planet. (VOY: "Muse")
According to the Star Trek: Star Charts, on page 25, Class L planets were "marginal" planets. They had an age that ranged from four to ten billion years and a diameter between 10,000 and 15,000 kilometers. Marginal planets were located within the ecosphere of a star system. They were categorized by a rocky and barren surface with little surface water and an atmosphere of oxygen/argon with a high concentration of carbon dioxide. Native lifeforms were limited to plant life, although the majority of Class L planets were suitable for humanoidcolonization.