Have you ever wondered why there are hairs up the inner margins of column wings in the
greenhoods? What? you didn't know that greenhoods had hairs up the inner margins of the
column wings?

Well, nor did the Column until Kevin Matthews sent photos of them adorning the column wings
about this time last year of Diplodium alobulum and D. trullifolium ...See Fig. 24 from
Taipa, 2nd August 2009.

Fig. 24. Diplodium alobulum at Taipa,
2 August 2009 by Kevin Matthews.

Note the white hairs on the inner margin
of the column wings.

The triggered labellum leaves only a small
space for an insect to crawl through using the
hairs for purchase thus ensuring glue from the
rostellum wipes onto its back before contacting
and dragging off the pollinia.

So the Column smiled, was this another distinguishing trait of his proposed D. "brumobulum" taxon (J77:18,23) with D. alobulum's Vee sinus to the synsepalum and D. brumale's turned down dorsal sepal and wide lateral petals? Not in the least. This was just another false lead, as it turned out, in the light of this year's awakening.

Close inspection of all the evidence showed that all self respecting D. alobula, in maturity, develop droop-snoot dorsal sepals and their lateral petals, especially in the far north, take on that D. brumale cobra hood look as in Fig. 25. They have fooled many, especially in those Sept/Oct field trips to Te Paki.

Furthermore, all the greenhoods have ladder like hairs up the inner margins of their column wings most of the time. Have a look at Bruce Irwin's drawings. There are exceptions on selected specimens it seems.

The drawings show no sign of hairs in the column of D. alobulum for instance. Undoubtedly Bruce's drawing specimen lacked them. But Kevin has found, in D. alobulum around Kaitaia, that this species has abundant hairs on some with very few on others.

Fig. 25. Diplodium alobulum a mature specimen from the waterfall,
Shenstone Block, Te Paki, 3 Sept 2000.

Allan Ducker mistook this, understandably, for D. brumale.
The Column has yet to see D. brumale anywhere in the far north
but at the time he noted the Vee sinus and dubbed it D. "brumobulum"
which is now dumped.

The Column was inspired to do a 3.5km trek up a deteriorating Otau to Cosseys track on 5 August to check on a large colony of D. alobulum seen there 18 years before. This common orchid is uncommon in the greywacke of the Hunua Ranges but the colony was still there. Like the Kaitaia specimens, they had hairs up the inner margins of the labellum wings and droop-snoots on the mature flowers.

D. "brumobulum" died at that moment; gone and unlamented! The Column tenders his sincere apologies for ever proposing this taxon and now has to amend the Journals index accordingly. Those wide droop snoot P. alobulum in the far north, still call for a fuller investigation, he muttered.

Why is this hair-ladder trait so consistent in the greenhoods? Bruce Irwin's drawings faithfully show them in all NZ greenhood genera, Pterostylis, Hymenochilus, Plumatochilos and Diplodium.

It seems that pollinating insects, entrapped by the triggered labellum and trying to escape through the column wings, use the hairs as ladder rungs for added leverage because of the drag of the sticky rostellum. Fig. 27 is an unfortunate fungus gnat pollinator inside a Pterostylis australis from Borland stream, 26 Jan 2004.

Fig. 27.
Pterostylis australis from Borland stream,
26 Jan 2004.

Microscopic column wing hairs below the
unfortunate fungus gnat may have been
too small to give it purchase to break free
from the rostellum glue sticking to pollinium gathered unwittingly from the previous
flower visited.

Note pollen on its back from a previous flower, clear glue on the rostellum, anchoring the gnat and only tiny ladder-rung-hairs on the margin of the column arm beneath; here pressed against a lateral petal.

Apparently the rungs were too small even for this small insect to get any purchase so it has succumbed because of it. Bruce's drawing shows no hair rungs on P. australis; too small to show at that scale no doubt.

Kevin pointed out that the hairs are always on the column wing's inner margins for a good reason; that is, to ensure that any insect aligned to clamber up these ladder rungs, automatically rubs rostellum glue onto its back before unwittingly attaching the pollinia with the glue.

That seems entirely possible and would explain why those column wing hairs, in that position, are all but ubiquitous in the greenhoods - even on those species assumed to be self pollinating.

The essential rostellum in greenhoods is not well known even though Dan Hatch depicted it clearly in his 1951 thesis [1] but it is otherwise difficult to find in the literature.

Fig. 29 by Ian St George, clearly shows the rostellum in "self pollinated" Pterostylis montana sensu Moore. It also shows its bulging heart shaped stigma (not present in P. montana s.s.) adapted thus to catch its own pollinia as they drop, as also clearly depicted. Note the hair-ladder on the inner margin of the column wing.

"Aha", you say, "why would self pollinating species have ladder rungs for non-existent pollinators?" Good question. How about pollinating greenhorn insects in greenhood species by mistake?

The Column is ill-at-ease with the concept of obligate self pollination because that is tantamount to obligate in-breeding and thus inevitable demise of the species. Triggering labella and ladder rung hairs in so called "self pollinating greenhoods", thus become a nail in the coffin of any obligate self pollination hypotheses. Both traits signify active facilities for insect pollination, occasional insects perhaps but visiting often enough to overcome the insidious effects of in-breeding.

"Then why does P. tasmanicum, with a non triggering labellum, have column wings at all? and why are they better equipped than other greenhoods, with ladder rung hairs, right to the top of the column wings?"

Excellent questions.

Firstly, that wagging, yellow plumed labellum is only an insect attractant, isn't it?

Perhaps the greenhorn greenhood pollinators, still crawl in at the base of the galea, where there is enough space, then clamber up between the column wings to escape because the other upward escape route is blocked, not by a triggered labellum but by 1) the lateral petals squeezing in, 2) back slanting yellow and white labellum spikes and 3) dense and interlocking column wing hairs, right up past the rostellum.

Fig. 28 from the Shenstone Block, Te Paki, 25 Oct 2001, shows those copious column wing hairs, the usual cobwebs, spider debris and a tiny insect skulking around, to add to the confusion.
Bigger bugs would need ladder rungs, for pollinating P. tasmanicum in the normal way.

Fig. 26 from 27 Sept 1997, shows no bugs but a fragment of its own pollinia on the base of the stigma, no doubt for fall-back self pollination after the insects have failed to cross pollinate it.

What do you think?

Fig. 29.

Pterostylis montana sensu Moore by Ian St George, showing the column with one wing removed.

Note the rostellum below the pollinia, hairs on the inner margin of the column wing, swollen heart shaped stigma having caught its own pollinium as it dropped.

Fig. 28.

Plumatochilos tasmanicum Shenstone Block, Te Paki, 25 Oct 2001, shows spider debris in copious column wing hairs which are squeezed by the lateral petals thus blocking one of the pollinator's escape routes leaving only, through the column wings past the pollinia.

The tiny insect on the left may be a red herring.

Fig. 26.

Plumatochilos tasmanicum with window, showing no bug but a piece of its own pollinium where it has dropped onto the base of the stigma and effected fall-back self pollination.

Both column wings show hairs at the tip, the remainder being obscured inside the wings.