Judith Doyle, of Wellington, asks :-
The photo I have attached is of a pohutakawa on Oriental Parade, Wellington. I have often wondered why the matted roots (or whatever they are) hang down in great clumps in midair from one particular pohutakawa tree but not all the others?
Gerald Collett, an aborist with Geotree Limited, responded.
I have often wondered myself why some pohutukawa Metrosideros excelsa produce beards of aerial roots and some don’t. I do not know why. Peers I have spoken to over the years have also not known why.
Possibly it is a genetic variation (a survival adaptation?) within the species? Or perhaps hybridisation with other Metrosideros, or something else instead or as well?
Northern rata (Metrosideros robusta, closely associated with pohutukawa) commonly germinates epiphytically and sends roots down the host tree. Pohutukawa also sometimes establish epiphytically. The two species are known to hybridise.
I have seen pohutukawa aerial roots descending from wounds on branches and trunks (as if stimulated by the wound), but this looks to me to be something different to the beards.
I have seen pohutukawa stems entirely sheathed in webs of aerial roots; again I think this is something something different to the beards.
Pohutukawa trunks and branches reclining on the ground (or collapsed onto the ground) will often produce roots where in contact with the ground (or from aerial roots that descend to the ground).
Pohutukawa aerial roots are known to run uphill (for example up the face of a cliff when a pohutukawa germinates on a cliff face), as well as sideway and downwards.
A search for ‘pohutukawa beard’ on the internet will find references to beards in various publications and papers on pohutukawa, and lots of photos.