Image from Steve Bowers
Quercus novis, a tweaked oak tree species growing on Garrow, a partially terraformed colony in the Outer Volumes. Such plants help to stabilise the soil and maintain the oxygen balance.

In the strictest sense plants are any of a major group of related Old Earth organisms that are multicellular, eukaryotic, exhibit embryonic development and, except in a few parasitic forms, capable of photosynthesis via chloroplasts that bear chlorophylls a and b that give them their characteristic green colour. They are the primary producers in all of the terrestrial and many of the shallow aquatic ecosystems of their native planet.

In common parlance, a plant is any biological organism, Terragen or otherwise, and natural or otherwise, that is sessile, autotrophic and photosynthetic. Some xenologists and biologists prefer to reserve the term 'plant' exclusively for Terragen species which are members of the Kingdom Plantae, and invent alternative terms for other life forms, such as 'plant-like organism', 'plant analog', or 'plantoid'; others extend the classification 'plant' to cover similar xenobiont equivalents. In taxonomy, each separately-evolved biota on a life-bearing world may include a number of different groups of plant-like organisms, each with different characteristics and evolutionary history. These groups of plant-like organisms are each given specific taxonomical designations, and all naturally-evolved extraterrestrial plant-like organisms are completely distinct from Terragen plant groups.

Plant-like xenobiota, neogen, synano or cyborg organisms, particularly sessile and/or photosynthetic examples are generally referred to as plants in common parlance. Inorganic beings like plantbots are called plants only by analogy. There are similar disagreements regarding the nomenclature for sentient but subsophont neogen, synano, and cyborg organisms that resemble natural Terragen plants.

The major Terragen plant taxa are;
1/ Cyanobacteria of various sorts. These are not included in the major Terragen plant groups, but the photosynthetic organelles of all other plant groups are descended from various ancient species of Cyanobacteria which have become endosymbiotic within their cells. More details here.
2/ Algae, including Red Algae, Green Algae and Brown Algae. These range from single-celled organisms to large aquatic kelp. Note that from a cladistic viewpoint Red Algae and Brown Algae are distinct from Green Algae, which are included in the clade Viridiplantae with the other green plants. Many species of algae have been genegineered to produce foodstuffs, fuels, medicines, construction material and other useful products. The term 'algae' is also used in common parlance as a general designation for extraterrestrial organisms which fill similar ecological niches, and also for neogenic organisms, hylotech and synanotech microsystems that perform similar functions.
3/ Terragen land plants, including mosses, liverworts, lycophytes, ferns, gymnosperms and angiosperms. Representatives of all these groups can be found in artificial habitats and on terraformed worlds throughout the Terragen Sphere, often geneered or otherwise enhanced for various purposes.

Terragen land plants are distinguished from the algae that gave rise to them by embryological development and complex tissues, including reproductive organs that they evolved in adapting themselves for life out of the water. Though they lack the morphological and behavioural complexity of animals, plants are biochemically diverse; able to produce a wide variety of organic compounds. Plants comparable to mosses and liverworts first appeared in the late Ordovician, and colonized wet areas during the Silurian; by the late Devonian they had evolved the full suite of features necessary for life on land, and formed the first forests. Initially, lycopods, sphenophytes, and various ferns were predominant, but seed-bearing plants such as the cycads, gingkoes, conifers, gnetophytes, and angiosperms eventually came to dominate the flora. The angiosperms, or flowering plants, became common over the course of the Cretaceous, and accounted for the vast majority of species thereafter.

Well-known examples of xenobiota that are plant-like (and are often referred to as plants) can be found on Trees, Chorus, Ridgewell, on To'ul'h Prime (though in the atmosphere rather than on the surface), New Gaia, Oshiq, Kammerer, Dante, Ararat and other members of the Garden of Paradise cluster, and on the various Cybyotan worlds.

Lazurogenic projects have created reasonable facsimiles of most major extinct Terragen plants, though because of the fragmentary nature of plant fossils there is a large component of extrapolation and imagination in their re-creation. Still, groves or entire forests of cordaites, lepidodendrons, bennettites, glossopterids, calamites, and various extinct cycads, conifers, and gingkoes are quite common today. Plants both baseline and gengineered play a very large role in agriculture, hab maintenance, and terraforming. In the case of dyson trees and orwoods, the plants are themselves the habitat. Plant provolves are relatively rare, due to the constraints of powering a sapient-level thought process exclusively from the energy that can be gathered from photosynthesis at a single site (see bradychronic plant provolves), but there have been a number of work-arounds for this problem as seen in such groups as the Alseids, Clade Keruing, or Dendrosequoia Sapiens.

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Development Notes
Text by Stephen Inniss
Additional material by Steve Bowers 2024
Initially published on 20 November 2010.