The blood of elves is not literally green, but it does contain a mysterious substance that has more in common with plants than with anything found in any other warm-blooded creature.

Elven blood teems with tiny organisms, so small that they would barely be visible under the strongest lenses Sevrin’s artisans can craft.  These organisms are similar in nature to algae, and like these tiny plants, they can transform sunlight into energy.  They are sensitive to light cycles and multiply quickly as the days lengthen. This explains, at least in part, why the Greening occurs when the long winter finally gives way to spring.

Philosophers might argue whether elves are hosts to this organism, or whether this is simply a part of the elven physiology.  Elves see no such distinctions and would view any such discussion with incredulity.  Humans tend to view themselves as islands with discrete boundaries. This is not a concept elves understand.

Elves don’t understand how humans can be unaware of the tiny lifeforms around and within them.  Elven sages have long studied these barely-visible worlds. They know that some organisms form surprisingly sophisticated colonies in which members take on different functions, and they know that non-contiguous colonies can communicate with each other.  It is believed that sound waves, too high for even elven ears to hear, are the means of communication. But thanks to the sensitivity of their crystalline bones, elves perceive the present of unseen life, and they have learned to communicate with the beings that live on both sides of their skin. Humans often note that elves seem “more in tune with nature.”  This is generally regarded as a metaphor, when in fact it describes the literal process rather well.

The ability of these organisms to communicate with non-contiguous communities is central to elven medicine, hunting, and warfare.  The energy greenblood gathers from sunlight can be shared among elves.  Several elves working together can heal a wounded elf, strengthen a laboring mother through childbirth, grant a sudden burst of strength to a spear-wielding elf facing a charging boar, or send speed and strength to a beleaguered fighter.  Humans have often observed that fighting three elves is like fighting ten men, but they are unaware of the ebb and flow of energy that makes this possible.