Varga plant

Varga plants were deadly plants native to the planet Skaro.

Biology
The Varga plants resembled large cacti, but with roots that allowed them to drag themselves along. They had the ability to poison other creatures with their thorns, making them into other Varga plants. An infected victim would first become homicidal. As the infection progressed, white hair would grow over their bodies. (DW: Mission to the Unknown)

The Varga plants that infested Kaalann were different in appearance, being more akin to a Venus Flytrap and immobile. Their venom also killed with a touch. (VG: City of the Daleks)

The spines could not penetrate the thick hide of a Slyther. (GN: The Only Good Dalek)

History
Varga plants existed since very early in Skaro's history. The name "Varga" meant "devourer" in the Dal language. Originally they could not move; instead they would wait until their prey approached them. Later, due to the chemical and radiological pollutants in Skaro's atmosphere and environment, they began to mutate so they could move. (DW: Mission to the Unknown, BFD: Purity)

By the 39th century, the Daleks had imported them to other worlds. When the Daleks set up a base on the planet Kembel they brought some Varga plants with them to act as sentries in the jungle surrounding their base. Jeff Garvey and Gordon Lowery, members of Marc Cory's expedition team, became infected. (DW: Mission to the Unknown)

The plant was again found on a terraformed Jupiter where the plant infected a large battalion of Earth Alliance troops. (BFDE: Dalek Empire II: Dalek War)

Following the Last Great Time War, Varga plants infested the ruined Dalek capital city of Kaalann. Though these could not move themselves, they had long, snapping "mouths" which excreted jets of venom. (VG: City of the Daleks)

When the operators of Station 7 took a section of petrified forest from Skaro, they took some Varga plants with it. These plants were similar to the ones used on Kembel, but possessed arms and legs, rendering them capable of full movement. (GN: The Only Good Dalek)

Behind the scenes
No snapshots exist from the lost episode DW: Mission to the Unknown. A publicity photo exists showing a Varga plant costume, with its actor's legs showing.