Journal Number 100
August 2006

VARIOUS CONTRIVANCES

Pterostylis
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.

The Pterostylis best adapted for insect pollination would have to be P. nutans. the "nodding greenhood".

In Australia it is one of the most widespread of the native terrestrials, but in New Zealand it
makes only occasional landfall, but soon dies out after a period of vegetative local spread.
In NZ it lacks its insect pollinator, and so forms no seed.

One can see why self pollination is impossible. The flower leans so far forward that any pollen
that does fall from its anther misses its stigma by a country mile.

To a lesser extent the same can be said for the insect pollinated NZ Pterostylis species -
P. agathicola, graminea, banksii, areolata for instance - the flowers lean forward, the stigmas
are flat, and the pollinia are cohesive, fragmenting only with difficulty. Self pollination is difficult,
but perhaps not impossible.

What NZ does uniquely have, is a group fully adapted for self pollination.

These have upright flowers with small openings, noncohesive pollen that fragments easily,
and prominent, often bulbous stigmas, that form a shelf to catch the falling pollen.

They include P. cardiostigma, humilis, paludosa, foliata and the little bronze grassland
P. montana agg. taxon structurally very similar to P. paludosa.

Pterostylis nutans
illustrations adapted from Bates & Weber.
Orchids of South Australia. Govt Printer, SA, 1990.
Note the nodding floral stance making self pollination impossible.

Self - Pollination Devices in NZ Pterostylis

Note the upright flower and prominent stigma of
A: P. paludosa;
B: P. montana agg;
C: P. cardiostigma;
D: P. foliata;
E: P. humilis.