Journal Number 101
November 2006

VARIOUS CONTRIVANCES

Gastrodia
The New Zealand terrestrial orchid flora is unique because most self pollinate:
the various contrivances by which the New Zealand orchids are fertilised by themselves are recounted here.

Gastrodia "long column" appears nicely adapted for insect cross pollination: it is highly fragrant at
least at some sites and at some stage of flowering, its pollinia and anther cap are easily dislodged
by visiting insects, and the pendant flowers prevent the dislodged pollinia from falling onto its own
stigma. Presumably an insect crawling into, then out of, the tubular flower, will take pollen with it in
some fashion.

In fact Gastrodia "long column" flowers turn upwards as they mature, allowing pollinia to fall onto
their own columns, so that self pollination can occur as a reserve position.

The observation of many bare stalks just after flowering suggests however, that neither insect
pollination nor self pollination is very efficient in this taxon. Gastrodia aff. sesamoides has similar
structures but sets more fruit.

By contrast, Gastrodia cunninghamii and G. minor have short columns, apparently a uniquely
New Zealand adaptation for self pollination in the whole genus of Gastrodia.

The closed tubular flower of G. minor hardly permits an insect to enter, and even if it did, any
disturbance of the anther cap and pollinia, placed directly above the stigma, would cause self
pollination.