Had a weird dream that was an Ars Magica scenario.
A Gifted child is pulled into a Magical Regio occupied by a thorny plant, and hangs impaled for 9? days before found and rescued by a Magus and made an apprentice.
I think the dream was about Odin and Rune casting, or maybe a Christ analogy. But then the dream segued into how the plant's sap was mixed into the apprentice's blood, causing the kid to have Warped Magic (thorny plants spontaneously grow inconveniently - from an ancient idea of mine)
But it was the Magical Blood - Mystic sap that confused me enough to wake me up.
What would plant derived Magical Blood give you?
A herbam affinity is the easy boring answer.
A few more colourful options.
Intertwined Magic - The magi makes no distinction between Corpus and Herbam. The magi can always use the higher total of Corpus or Herbam for any effect which uses Corpus or Herbam, including requisites. Any lab notes made by an intertwined magic user, if they used the other form, only an intertwined magic user can use the notes.
A small digression - This could work for a bunch of forms - animal/corpus, especially for Bjornaer types, animal/herbam for druid types, Mentem/Corpus for a spiritual type who sees us all as one, etc.
Plant infused body - When wounded, the character bleeds green, and there is a noticable green tinge to their skin and eyes, and their hair presents a bit like vines.
All wounds are considered 1 level less when calculating penalties. When well rested and fed, each morning the characters recovers from 1 light wound. All recovery and again rolls have a 2 point bonus
An ability to cast a herbam spell.
Wall of Thorns, Converse with plant and tree are good examples.
A permanent herbam effect
Repel the wooden shaft, as nature will not strike their chosen one.