Phyllachora cibotii on Tree Fern (Cibotium glaucum)

The  tree fern Cibotium glaucum is endemic to Hawai‘i and is present on all major islands except Maui.  The fungus Phyllachora cibotii, an ascomycete of the order Phyllachorales, was described by Charles Hodges (1981) as a new species.  As such, the fungus is one of only eight species of Phyllachora reported on ferns throughout the world.  To date, the fungus has been found only on the island of Hawai‘i, although its restriction to this island may be due to lack of observation rather than to preference of the fungus to a restricted habitat.   However, the fungus does appear to be restricted in host range to C. glaucum, and has not been found on either C. chamissoi, which is commonly associated with C. glaucum as an understory tree fern in ohia forests between 600-1.500 m elevation, or on C. hawaiense, a less common tree fern in the rainforest understory. 

The fungus appears as dark, well-developed stromata (fruiting bodies) arranged linearly on frond stipes.  Perhaps as many as 1000 such structures are produced in heavily infected stipes, appearing more frequently on the under surface than the upper.  Its restriction to a single endemic tree fern host suggests that the fungus has evolved with its host and is itself endemic to Hawai‘i.  Because of this association, the host and parasite are well adapted to one another and the fungus appears not to damage the host significantly.  Microscopic characteristics of P. cibotii are described in Hodges' paper (1981).

   Stromata of Phyllacora cibotii in a typical linear arrangement on a frond stipe of Cibotium glaucum (Photo by C. Hodges).