Sentient plant life whose seed pods were violently scattered across the cosmos whenever volcanic eruptions on their home planet occurred. Two pods arrived on Earth at the South Pole during the Pleistocene era and were uncovered towards the end of the twentieth century. One Krynoid pod hatched after being exposed to ultra-violet light, its tendrils gouging into the flesh of a nearby scientist.

Within hours, his chemical make-up was changing into that of a plant, his body undergoing a similar metamorphosis. This Krynoid was destroyed by a bomb, but the second, unopened pod was taken to England by people employed by Harrison Chase, the millionaire botanist. Chase caused the second Krynoid to latch onto one of his men, but was determined to keep it under laboratory conditions.

The Krynoid was too strong however, growing at an astonishing rate and controlling all plant life for miles around, as well as establishing a sympathetic telepathic link to Chase. Impervious even to UNIT's high-density laser blasts, it eventually grew to the size of a cathedral, and was only destroyed when the RAF bombed it to pieces, shortly before it could germinate.