Entropy · Board game rules
What is the Life Card limit: 1 of each type or 3 of anything?
Quick answer
It's 3 of anything — each Planet can hold a maximum of 3 Life cards total, regardless of type.
Details
The rulebook states plainly that "each Planet is limited to 3 Life cards and you cannot play a Life card to a Planet that already has 3 cards next to it" [p.9 — Actions]. This limit applies to the total count of Life cards on that Planet, not per type — so you could have any mix of Bacteria, Plant, and Animal cards up to 3 total.
Note this is separate from the Lifeform token limit: each Planet can also have a maximum of 5 Lifeforms of each type (Bacteria, Plant, Animal), which is a different limit tracking the tokens gained from cards, not the cards themselves [p.9 — Actions].
Watch out: Don't confuse the 3-card limit (cards played to a Planet) with the 5-token limit (Lifeforms of each type on a Planet) — they track different things and have different caps.