The mustard-yellow fruitbodies of Hemitrichia
calyculata are only a few millimetres tall. As the sporangia mature, the outer wall
(= peridium) breaks away and the internal mass (capillitium and spores) flounces out like
cotton candy and forms a top-shaped head. The heads sits in a shallow cup (= calyculus)
that is a persistent remnant of the peridium. The support stalk is short and blackish.
This species is very common throughout our region. The sporangia are produced on logs or
stumps in hundreds. When very young, they are a brilliant vermillion to cinnabar colour
and are easily spotted. Hemitrichia clavata is very similar but the basal cup (=
calyculus ) is much deeper and the fruitbodies are thinner and club-shaped to pear-shaped
rather than top-shaped.
In all species of Hemitrichia the threads of the
capillitium are marked with spiral thickenings along their length. As with Arcyria,
changes in relative humidity cause moisture to be taken up or lost by the threads and this
results in changes in tension along the length of the threads. Adjustments to these
tensions causes the threads to wriggle and eject the spores for dispersal by the wind.