Can anyone tell me what species of prothallus this is? Came with a blood orange tree I bought here in CA. Thanks in advance

Welcome to the site! A pic would help!

Oops! I guess it didn't upload 🙈

Looks like a lichen

first thing come to mind for me was a new beginning colony of pixie cup lichen
but can not find an image of a new colony
???

OH! Lichen! Very cool, I've transplanted it and will see how it continues to grow. Thank you for both of your inputs

Its a Liverwort, a cool plant that likes cool shady wet spots. You can transplant them (to shady wet spots) and grow entire colonies. There are a few native to California but, I don't know if that's one of them. Wait until you see it 'bloom' (not sure that's the right word) - it looks like a miniature palm tree forest.