Green Party candidates tend not to win races in national or state/provincial legislative races conducted by plurality. The type of constituency Green parties cultivate is systematically under-represented by an electoral system that privileges regional concentration as the only way a smaller party (measured by jurisdiction-wide votes) can win representation. Nonetheless, even Greens are bound to have some local concentration, as a few near misses in recent Canadian elections discussed here previously have suggested. It seems it would be only a matter of time before some Green candidates begin to break through in FPTP jurisdictions, given the greater salience recently of the party’s signature issues.
In the UK, a recent local council by-election suggests growth within the range that would be needed to win a seat in the next general election. The seat in question is in Brighton, and bears watching.
Update: In light of interesting comments from readers regarding Greens in Australia and New Zealand, I have now cross-planted this in those country blocks.