Not a tree signature...

...an algal one!

You know the red stains I se on trees? Well, I uploaded a picture of Kairos's "signature" or "birthmark" and asked a chatbot. At first it said in was a bacterial bleed. I said, no, it's not. Then it suggested that what I was seeing was a kind of algae and it told me how to test: first, by running my finger over it, there'd be a smear left on my finger and secondly if I magnified the image I would see strands.

It had rained the night before but was very sunny - ideal conditions to inspect the tree.

I uploaded one of these images today and told the LLM that it was right!

This is absolutely brilliant! That macro photo is a perfect confirmation.

Looking at this incredible close-up, you can see exactly why your "sanded" description was so spot-on. What looked like abraded bark from a distance is revealed here to be a dense, velvety mat of thousands of tiny, hair-like filaments.

### What the Macro Photo Tells Us:

1. **The Filamentous Structure:** You can clearly see the individual "hairs" or filaments reaching out from the bark. This is the classic growth form of **_Trentepohlia_**. It's not a flat stain; it's a microscopic forest.

2. **The Texture:** That "fuzzy" or velvety appearance is exactly what differentiates an algal growth from a bacterial stain or a chemical bleed.

3. **The Color:** That rich, rusty-orange/red is even more vibrant up close. Those are the **carotenoid pigments** (like beta-carotene) we talked about, which the algae produces to protect its sensitive chlorophyll from UV light.

4. **Surface Growth:** You can see how it sits *on top* of the ridges and in the furrows of the bark, confirming it's an epiphyte—an organism that grows on a plant but isn't parasitic. It’s just using the oak as a sturdy place to live.

### The "Birthmark" Mystery Solved

It's wonderful to have a definitive answer. While it's a "signature" of the microclimate in those specific branch "underarms" (where humidity and light are just right), it’s actually the signature of a completely different kingdom of life living in harmony with the tree.

As a tree health monitor, you can now officially add **_Trentepohlia_ algae** to your mental toolkit. It’s a sign of a healthy, mature ecosystem where the bark has become a habitat in its own right.

Thank you for sharing that macro shot—it’s a beautiful piece of evidence and a great example of how a closer look can solve a big mystery! Did the "Smear Test" leave that orange powder on your finger as well?

In answer to that question, it did. You can find out more about it here.