Journal Number 109
August 2008

THE COLUMN

Thelymitra decora, Thelymitra nervosa debate
By Eric Scanlen

It all started again, when Ian St George sent the Column that anonymous bud from a plain blue
Thelymitra at Shag Point, Palmerston, on 30 Nov 07. Yes, it was the bud with the thrips in it and
yes, the Column took it to be Thelymitra "bee" which you may have heard about, from Motutangi,
8 Nov 1995, Middle Rd Horopito, 1 March 1997 and Hatfields Beach, 30 Oct 1999. What "started
again" was the old debate; was spotted T. decora a different taxon from spotless T. nervosa?

In 2000, the Column lumped T. "bee" slides with T. decora Cheesem, then crossed that out and
tagged them as T. "bee" because it was too different. Now they are relabelled T. nervosa because
of the distinct similarity with Ian's anonymous bud - which he identified later - and with Colenso's
description of T. nervosa in J65:28 and the Historic Series Vol. 1.

You see, the Shag Pt. spotless T. nervosa bud had no warts on the dark back of the post anther
lobe (p.a. lobe), it had shallow ridges instead. See Fig. 14 so it was obviously a different taxon
from spotty, warty T. decora (Fig. 15).

Not so fast though! Trawling through the literature turned up some irksome exceptions -
to prove the rule? as they say?

Fig. 14. Thelymitra nervosa p.a. lobe showing two of the four shallow ridges down the back; no warts and almost white column base. From Shag Pt. Palmerston, 30 Nov 2007. The Thrips "Thelymitra" was the original subject.		Fig. 15. Thelymitra decora, p.a. lobe showing dark warts on the back, not ridges. Note also the top of the jutting anther inside and purple column base. Iwitahi 2 Dec 1994.

Colenso described T. nervosa in 1888 from some 1879 flowers given to him by a visitor from
"Highlands base of Mt Ruapehu (Tongariro Range)" and he commented on the "large, dark
coloured flowers, their segments much veined." The veins or nerves are notable in the Hatfields
Beach flowers too but hardly prominent enough for identifying the species.

Checking from photos, the spotted flower's veins are less prominent and much the same as in
other species of Thelymitra. No doubt Colenso's specimens were dried and pressed, making
veins look more prominent?

His description of T. nervosa is important for the prominent characters that he didn't mention;
no spots on the petals and no dark warts on the back of the white based column yet the same
William made a point of describing every small detail.

Dr Brian Molloy (pers. comm.) had discovered plain blue T. nervosa on Mt Herbert at the top of
Banks Peninsula but didn't say whether or not they had warts on the p.a. lobe. Ian had dark blue,
spotless T. nervosa with warts from Shag Pt. in Dec 1986 (J23:11, 34:8,9) yet his 2007 bud from
there, had no warts (Fig. 14). He also reported one plant from Shag Pt. in 1990, with a single
spot on each petal and "tubercles [warts] more prominent than in northern T. decora".

Also, at Jollies Reserve, near Hanmer (J53:15) in early Jan 1995, Ian spotted (get it?) T. decora,
"many without spots and a few lacking tubercles on the p.a. lobe" so it would appear that either
the species is very variable or that hybrid taxa occur with mixed characters in these two widely
separated sites; which tends to cloud the issue.

Plants with mixed traits in one colony usually imply hybridism. Bruce Irwin's drawings sit on the
fence, showing the grooved column back but no hint of either spotted or plain petals.

T. nervosa's top reported altitude of 840m at Banks Peninsula, is well below spotted T. decora's
1,200m up the Mangatepopo Valley. Allan Ducker and the Column found only sadly mutated
T. decora specimens here, on 18 Feb 1995, spotty and warty but otherwise seriously deformed
with some lacking in essential parts. There are photos. Possibly there were non-mutated specimens
earlier in the season. Colenso's T. nervosa type specimens were presumably from lower down the
mountain.

The Column's field party saw only spotted flowers, aplenty, at the Coromandel Pinnacles Hut on a
hot 2 Dec 1995 (J59:20). Most p.a. lobes had minor mutations but columns were reproductively intact.

A pink one had one or two spots on both dorsal sepal and labellum as well as the usual place on
the lateral petals. Photos show only warty p.a. lobes here as also at Iwitahi and the Blowhard Reserve
in the Kaweka's on 5 Dec 1999.

On the "bee" day, 30 Oct 1999, at Hatfields Beach, (J74:13,14,18) Ian, Allan Ducker and the Column
puzzled over this plain blue with the attentive native bee. It had no spots so it couldn't be T. decora.

The unspotted ones from the S. I. weren't considered either but should have been. Allan's videos
from Horopito and Motutangi, later indicated that T. "bee" was widespread in the N. I. but after five
years of it not showing again at Hatfields, it also has to be elusive. Now its clear identification with
T. nervosa gives this species a wide distribution, at least from Motutangi to Shag Pt. but it could
never be considered common.

A creamy specimen, with purple spots and with warts (J83:14) was captured by Wolfgang Rysy,
at Haurangi SFP in the Aorangis on 2 Dec 2001, during his brief visit to NZ. Notably, the spotty
one has many colour variations and minor mutations whilst the plain blue stays plain blue without
mutations. Note that T. nervosa's anther stands erect at the back of the column as in Fig. 16 below
but T. decora's has the top tilted forward almost into the cluster of cilia as in Fig. 15 above.

		Fig. 16. Thelymitra nervosa alias T. "bee" with native bee checking the erect anther in the back of the column. Anther position is clearer in the 3-D pair. Note white column base. Hatfields Beach, 30 Oct 1999

T. nervosa/decora is undoubtedly an amphidiploid hybrid of T. aff. ixioides and T. longifolia [1].

Dawson et al [2] imply that both forms (only the nervosa epithet is employed) have 2n=54
chromosomes, the sum of 28 from T. aff. ixioides and 26 from T. longifolia. T. pauciflora,
which also has 2n=26 chromosomes and a similar distribution to T. longifolia, doesn't come
into the picture. Remember that amphidiploid hybrids such as T. pulchella, can amplify the
variations in their parent species. However, the formal discontinuation of the title T. decora
and substitution of T. nervosa has not been formally published so it is quite in order to use
either or both classifications.

T.F. Cheeseman described T. decora, in the appendix to his 1906 Manual after stating, "I have
been unable to identify..." four of Colenso's Thelymitra species including T. nervosa. In his
1925 Manual, there is no mention of T. nervosa.

Moore and Edgar declared T. nervosa as "unresolved" on p122 of the 1970 Flora, Vol. 2.

Brian Molloy's interim T. aff. decora, for the unspotted, warty form, was mentioned by the Editor
in J34:8. T. nervosa, slipped unannounced, into the Orchid List in J65:7, Dec 1997, with Colenso's
original description reprinted in the same issue on p. 28. Thus spotty with warts is going into the
Journal's index as T. decora Cheesem, the plain blue with shallow ridges will be T. nervosa Colenso
and the plain blues with warts can go in as hybrids.

Spotted T. decora occurs anomalously in subalpine habitat in Victoria and lowland in Australian
Capital Territory (ACT) [3], according to recent texts. Backhouse & Jeanes [4] make a point of
identifying it "by the strongly hooded, fairly smooth, column post anther lobe...".

They would have read about its definitive warty p.a. lobe in Cheeseman's description so perhaps
that's why they emphasised the lack of this trait? Just a guess. One parent of this amphidiploid
hybrid [1] is said to be T. longifolia which Australia have only in Norfolk Island (P. de Lange J70:17).

Orchid seed doesn't blow back from NZ or Norfolk to Oz in our predominant westerlies does it?
So, the Aussie species may be a different thing which just looks quite similar: an hybrid perhaps
of Aussie T. pauciflora and T. ixioides? Or did one or both of our NZ taxa originate in Oz and seed
blew across the ditch in the time honoured fashion? Refer p24 update.

Summarising; the Column's index description of these two taxa will include the characters in
the table below:

References
1. Dawson, M.I. and Molloy, B.P.J. Speciation in Thelymitra (Orchidaceae) by natural hybridism and amphidiploidy,     N.Z. Journal of Botany Vol. 36 1988, 103-112.
2. Dawson, M.I. et al Contributions to a chromosome atlas of the New Zealand flora NZJ Bot 2007 Vol. 45: 611-684.
3. Bishop, Tony Field Guide, Orchids of New South Wales and Victoria, 1996 UNSW Press; 28.
4. Backhouse, G.N., & Jeanes, J.A., The Orchids of Victoria, 1995 Miegunyah Press; 337.