This actually refers to an entire order of trees that grow primarily on lava. Note that the word ‘trees’ is very much an approximation; lachnimloth are ‘organic’ in the sense that they have a recognizable life cycle, and obey universal biological imperatives. They are absolutely neither carbon-based, nor part of an oxy-nitrogen ecosystem.
But lachnimloth are still very pretty. Extremely dangerous to humans in their living form, thanks to the heat, but very pretty. It’s all due to their makeup: the various species of lachnimloth are made up of a complicated mix of glass and trace materials. When alive it has molten glass for sap and various translucent silicates for bark and ‘flowers.’