How do you interact with the green plant like things?

To access these hidden passages you need to find the Three Gnarled Tongues

Getting this relic involves completing the Egg of Deformity side quest

Items needed

Can be found in the Desecrated Cistern.

Sold by Candelaria for 800 Tears of Atonement in the Graveyard of the Peaks.

Found at the end of the top room above the Ceremony Room in the Grievance Ascends area.

To get the egg, place the Black Grieving Veil, Torn Bridal Ribbon and the Melted Golden Coins on the plates in the cave of the bottom of Grievance Ascends in front of Altasgracias.
Take the Egg of Deformity and put it into the tree as an offering where Perpetva is first encountered in the Mountains of the Endless Dusk. Leave the scene and return to receive the Hatched Egg of Deformity.
Take the Hatched Egg of Deformity to the blessing statue in the Lake of Silent Pilgrims accessed via the fountain in Albero to receive the Three Gnarled Tongues Relic.

Quest notes from: https://blasphemous.fandom.com/wiki/Three_Gnarled_Tongues