A Heligan Tree is a genetically engineered type of space-borne plant life, similar to a huge tree with a nutrient-rich orb of roots in its centre and countless leafed branches growing outwards in all directions, forming an elaborate structure. They are used by Human colonists to convert carbon dioxide into oxygen in the upper atmosphere of alien worlds, making them suitable for colonization. Enormous Heligan forests are known to float in the upper atmospheres of planets in the Cygnus Sector.
The Heligan Tree appears to reproduce asexually, as it produces mobile spores which are later launched into space to grow into a new individual. Presuming the Heligan Trees' metabolism is anything similar to Earth trees, they probably need to recycle water and nutrients from the bodies of their deceased neighbors, as photosynthesis alone would hardly provide these.
- The Roots of Evil, by Philip Reeve (2013)