Burgeoning Spiderwort mold
You may have seen a bulbous structure lurking where berry-bearing Burgeoning Spiderwort plants had once grown. This is the Burgeoning Spidewort mold. While its actual name is unknown, this fungus appears occasionally when you have not harvested the Spiderwort's berries in a few days. It is destructable, so if you spot it, take a medium-large group of Pikmin to the area and have them attack it. Soon enough, the mold and its thread-like hyphae will slowly disappear, allowing the Burgeoning Spiderwort to grow once again. This is not harmful to your Pikmin, only to the plant.
Locations of the mold
Valley of Repose
There are none in the Valley of Repose, due to the harsh climate and lack of fertile soil for the growth of the Burgeoning Spiderwort.
Awakening Wood
There is a large mold near the landing site, where two Spiderworts grow. It seals away both of the plants, but when eliminated, they will grow back.
Perplexing Pool
There are two of them across from the landing site (near the location of the Gherkin Gate). There is a pesky Swooping Snitchbug here as well as a Watery Blowhog, so you may want to defeat them first.
Wistful Wild
There are three molds in a large clearing near the drainable lake. Each one covers its own berry plant, so it may take a while to get rid of them all.