In 1826 Allan Cunningham found an orchid on rocks in the bed of a stream
near Whangaroa.

Eleven years later he described it in the Precursor to Florae Insulare Novae Zealandiae 1837; not in the correct genus, Nematoceras (Corysanthes) but
as Acianthus rivularis, unfortunately without mention of leaf shape or length
of dorsal sepal.

Thomas Kirk in 1864 collected the same plant at Great Omaha near Leigh,
but in error named it Corysanthes rotundifolia.

A year later Kirk found a brand new Corysanthes on Great Barrier Island.
This plant had a leaf very like that of Acianthus sinclairii, so Kirk not aware
that he had actually seen Corysanthes rivularis at Great Omaha, reasoned
that this must be Cunningham's Acianthus rivularis and incorrectly identified
it as such.

This series of misidentifications resulted in utter confusion of Corysanthes
species for more than 100 years, until Mark Clements located the type
specimen of Corysanthes rivularis in the Lindley herbarium at Kew and
recognised it as the plant then known as Corybas orbiculatus.

The foregoing notes, which demonstrate how easily an imbroglio can be
spawned, drew heavily on Dan Hatch's more complete account on pages
3-4 of NZNOG Journal No.17.  I recommend you read it.

The revelation by Clements left Kirk's great Barrier plant, previously
erroneously called C. rivularis, without a name. Clements and Dan Hatch
jointly named it Corybas acuminatus.

Actually by then it had become clear that the name C. orbiculatus was applied,
not to a single species, but to an aggregate of several undescribed species of
which C. orbiculatus with its comparatively short tepals and long, scoop-
shaped labellum was an uneasy component.

So now the identity of C. rivularis is clearly understood?  Well not quite.  
Several different taxa are included under the name C. rivularis.
They are now regarded as the Nematoceras rivulare aggregate.

Since 1985, with willing help from Taranaki orchid enthusiasts, I had recorded
distributions of the two forms I was aware of and had tag-named Corybas "A"
and C. "Mt. Messenger", neither of which extend as far north as Kerikeri
(C. rivularis territory).

Almost every year a quite distinctive form of Corybas came to our attention
and could not be ignored. The first of these (tag-named C. "short tepals")
was shown to me by Rob Ward at Rerekapa in north Taranaki. I immediately
recognised it as a plant I had seen 40 years previously near Wanganui.
 Subsequently Dr Molloy found identical plants at the type locality of
C. orbiculatus, so that is now its valid name.

C. "Waiouru" also had a "valid" name, C. macranthus var. longipetalus Hatch.
However it clearly belonged in the C. rivularis aggregate. By then it had been
deemed worthy of specific rank but could not be named C. longipetalus as
an overseas species already bore that name. The problem was solved a few
years later when the genus Corybas was revised and split into several genera.
At last the plant has a correct valid name as Nematoceras longipetalum.

While I was studying these plants, the generic name Corysanthes, after
acrimonious discussion was changed to Corybas. Up to this point I have
used both these names in this account because at that time those were the
generic names in use. Now however, the genus name Nematoceras has been
reinstated to accommodate most New Zealand species, so it is appropriate
to use that name for the remainder of this article. I hope this will not be
confusing.

So what is the plant we must regard as N. rivulare s.s.?  N. "Kerikeri" was the
obvious contender for that title and is now universally accepted as such
(because it is found near Cunningham's original collection locality).

Several further forms have not yet been dealt with. They are Nematoceras
"whiskers", N. "rest area", N. "Kaimai", N. "ratty", N. "sphagnum", and N.
"Mangahuia". What is to become of them? They do exist and should be
acknowledged by botanists.

In my opinion the first two orphans ("whiskers" and "rest area") should be
accorded specific rank. Nematoceras "whiskers" has been recorded from
many North and South Island localities. It is probably the same taxon for
which HB Matthews prepared a manuscript description as Corysanthes
"viridis".

Diagnostic features are

1. Although very much like N. papa in general appearance, N. "whiskers"
   appears much more rounded when viewed from the side. N. papa on
   the other hand is ± compressed from front to rear.)
2. Labellum auricles are very large, flaring and often strongly tilted
   forward.
3. The colour pattern of N. papa is unique among known New Zealand
   Nematoceras species. When seen in longitudinal section, the upper
   / rear labellum margins show a plain green stripe. N. "whiskers"
   (and other forms) do not. Admittedly this clear stripe is often not
   noticed, due to inward folding of the upper labellum margins, but is
   there on N. papa only. Un fortunately my illustration accompanying
   the description, does not show a green margin (on the longitudinal
   section). However it is evident in the view of flower from the front.
   At that time I was not aware of the significance of this character.
4. The pale stubble of short hairs on the inner surface of the labellum,
   responsible for the tag-name "whiskers" is not prominent unless
   side lit. However it effectively obscures the pattern of veining on the
   apex.
5. N. "whiskers" is often found in damp, shady habitats. It can however,
   also be found in apparently well drained sites, near ridge tops.
   Other green flowered forms can not.
6. Unlike any other greenish forms, N. "whiskers" is quite strongly
   scented and therefore attractive to small flying insects. I suggest
   that a future name for this taxon should if possible acknowledge
   its scent.

The other form which I consider deserves species status, is another green
flowered plant tag-named N. "rest area". Its distinguishing characteristics
are

1. It may sometimes show a very short leaf petiole, whereas N. papa
   seems strictly sessile and N. longipetalum normally has an obvious
   petiole. Perhaps not a useful character - a very short petiole may
   escape notice.
2. The dorsal sepal is rather narrow and quite often arches up well clear
   of the labellum which itself adopts a chin up attitude so that its apex
   reaches down only to auricle level. It is tempting to think that the
   plant is afraid of drowning if it relaxes this very erect attitude.
3. After all it chooses very wet habitats in bogs or the very beds of
   shallow water-courses where the root system is probably below
   water-level for weeks, even months at a time.
4. I have seldom found a viscid disc on N. orbiculatus, on N. "rest area"
   never. This lack encourages self-pollination, so unlike other known
   N.Z. species, both taxa form viable seed pods on almost every
   flowering plant.

I am much less confident about the status of the several remaining forms
I have tag-named. I think it necessary to carry out careful field work before
they are finally categorised.

Now let us consider Nematoceras "Kaimai". I have long considered this form
worthy of specific rank but was always conscious of its resemblance to
N. "Kerikeri" (N rivulare s.s.).

Why is N. "Kerikeri" apparently restricted to the far north of the North Island,
apart from one or two small colonies on the banks of the Te Henui River in
New Plymouth?

Also why does the much more plentiful form, N. "Kaimai", apparently not
invade the territory of N. "Kerikeri"?

Could they be rather unalike forms of a single species? I now think they are.
You may think this suggestion is outrageous.  Perhaps it is. 
I'd welcome your opinion.

N. "Kerikeri" has a dark red labellum, N. "Kaimai" has not, and the distribution
of red in the longitudinal section is usually quite different. Also although both
forms have unusually long labellum floors between the inner and outer
flexures, that of N. "Kerikeri" is a little longer.

Yes, they appear so different it is hard to believe that they are a single species.

Ah, but here is an interesting point. I was one of a family of five. Both parents
had black hair and brown eyes, as did four of their children. Joyce, the third
born, however had flaming red hair, freckles and blue eyes. Even her facial
features were different. How could that possibly happen? Uncle Tom (our
mother's brother) was a male replica of Joyce. He even shared her sunny
disposition.

Do I have any evidence to support my belief that N. "Kaimai" and N. "Kerikeri"
could be a single species? I think I do

1. Both forms are structurally similar, though not identical.
2. Both are late flowering; N. "Kaimai" in late October near Tauranga
   N. "Kerikeri" in November. Remembering that Nematoceras generally
   flower later at lower latitudes, flowering times could be regarded as
   identical.
3. Although N. "Kerikeri" is usually much "redder" than N. "Kaimai", especially on the "cheeks" within the throat of the labellum,
   occasionally N. "Kaimai" approaches N. "Kerikeri" in this respect.
4. The peduncle of N. "Kerikeri" is usually a strange purple colour,
   (almost violet). Other forms of N. rivulare aggregate generally show
   little purplish flecks or flushes but occasional flowers of N. "Kaimai"
   approach this peduncle colour. More significantly some Te Henui
   flowers of otherwise very average N. rivulare s.s. has an almost
   totally green peduncle.

Tricia Aspin's Nematoceras "Pollok" is possibly even closer to N. rivulare s.s.
than N. "Kaimai". Perhaps they both would be comfortable as sub-species
of N rivulare.

Before discussing the remaining forms I have tag-named, I need to comment
on N. iridescens, N. longipetalum and N. papa.

N. iridescens has always troubled me. It seems very susceptible to changes
in growing conditions. I once found a small colony on a particularly sour
spot on a long, weeping N. iridescens clad bank. The flowers on the sour
spot appeared so different from N iridescens that at first I thought them
to be a separate species. Close examination revealed that all apparent
differences must have been due to poor nutrition and consequent arrested
development.

One common aberration is poor development of the bead-like gland at
the drop-off into the column cavity, said to be prominent in the published
description. Can all these faults be attributed to arrested development?
Perhaps not.

Until October 2000, I thought N. iridescens kept very much to itself and
never hybridised with other species flowering alongside it. However strange
colonies exist near Makatote Viaduct. None of the plants are quite like N.
iridescens: none are quite like N. papa nor N longipetalum but every
conceivable combination of the three. N. iridescens and N. papa seem the
most likely parents, but I had long wondered if N. iridescens and N.
longipetalum had shared a common ancestor in the dim past. Both have
distinctly petiolate leaves and though near its type locality, N. longipetalum
is mainly green with reddish markings; in some areas, the flowers can appear
almost as dark red as N. iridescens.

Now let us consider the large number of Nematoceras tag-named Nematoceras "a" (not quite Nematoceras "A"). They do not fit snugly the description of N.
iridescens so perhaps they should be regarded as a separate species.
I think not. Perhaps the description of N. iridescens could be amended to
admit these non-conformists.

N. "Mangahuia" on the other hand leans towards N longipetalum. It would
not be comfortable as N. iridescens. Also it is known from a single locality,
so I think it (and possibly N."sphagnum") should remain tag-named until
more fully understood.

Oh! One more tag-name springs to mind - N. "ratty". Maureen Young sent
flowers from near Warkworth before I had realised that N. "whiskers" was a
distinct species. N "ratty", I realised was just a very small form of N. "whiskers".
The column has chided me for not publishing the demise of that name.
I do so now.