The Krynoid

The Krynoids travel through space in pairs and two seedpods of the intelligent parasite weed fell to Earth and were frozen in permafrost. The first was eventually destroyed by the Doctor, but it burst and infected a human, which converted him into a Krynoid. The Krynoid are a carnivorous planet, which releases thousands of lethal pods into the atmosphere. The second Krynoid was taller than a house and it took over control of the surrounding planet life. The Phantom jets destroyed this Krynoid just before it was going to germinate.

Harrison Chase was a millionaire who was obsessed with plant life and this led him to steal and grow a Krynoid. He became compost after being put into his own crushing machine.

The Krynoid was only in The Seeds of Doom