According to MW3, "rimu" is "a tall New Zealand timber tree." It's a Maori word.
I probably won't post too many plant names in this blog; as when playing Fictionary, I get a little bored with definitions that basically just say "a plant from [place]." But I'll probably post a few now and then.
This word and the previous one appeared in stories submitted to SH, which is interesting because it's pretty rare for a submission to contain a word I don't know. (No need to take that as a challenge.)