I have no idea what this is, but I'm guessing some sort of fungus. We have had a lot of rain lately and I found this on the door to my garden shed.
Lignicolous on rotting nikau (Rhopalostylis baueri).
Stemonitis is a distinctive genus of slime moulds found throughout the world (except Antarctica). They are characterised by the tall brown sporangia, supported on slender stalks, which grow in clusters on rotting wood. Identification within the genus is difficult, and can only be performed with confidence using a microscope.