The kingdom of plants used to include all organisms that grew in the ground or could photosynthesis (or had obviously evolved from photosynthesising ancestors, such as parasitic plants like broomrapes). Fungi, which grow in the ground but which do not photosynthesis, have long been recognised as a separate kingdom. Now, many photosynthesisers are also known to be unrelated to the true plants (e.g. the cyanobacteria or 'blue-green algae') and some of the seaweeds (e.g. kelps), while the red algae are seen as distant relatives to the true plants, sometimes known as Virdiplantae ('green plants'). The green plants include green algae, mosses, liverworts, hornworts and, the best-known and most familiar plants, the vascular plants, which include ferns, conifers and flowering plants.


The vascular plants of Shetland are extremely well-known thanks to the work of the Shetland-born botanist Walter Scott (dates) and his colleague Richard Palmer (dates) who produced a checklist of Shetland plants in 1969 and a county flora in 1987, the latter updated in lists produced by Scott in 1999 and 2011.