Riverfruit

Riverfruit was the name given to a form of plant life native to the planet Alzarius by the humanoid Alzarians.

Riverfruit resembled Earth watermelons to some degree and appeared to be part of the staple diet of the Alzarians. It appeared to be farmed by the Alzarians, with riverfruit theft a relatively serious offence.

Immediately prior to and during Mistfall, the eggs of the Alzarian spider appeared within riverfruit. These would rapidly develop until the fruit split open and released the adult creature. (DW: Full Circle)

Given this development and the accepted link between the Alzarian spider, the Marshman, and the Alzarian humanoids, it is reasonable to assume riverfruit also contains the same unusual cellular characteristics as the descendant organisms.