Journal Number 94
February 2005

ORIGINAL PAPERS

Rodgers Got It Right - Prasophylla Are Difficult
By Bruce Irwin

My first encounter with Prasophylla was on Mount Egmont. I remember them as rather
nondescript plants, all parts of which were an almost unvarying  yellowish or reddish green.
A knowledgeable amateur botanist informed me that they were Prasophyllum colensoi.
I didn't doubt his identification. I still don't.

Later in other areas I found similar plants, all of which I regarded as P. colensoi. My first careful
drawing, made on Christmas Day 1952, included enlarged details of the column, showing that
the column wings were much shorter than the anther. That plant was from the Tararua Range.

Then about 1968, Dr Lucy Moore asked me to draw flowers of Prasophyllum colensoi, held in the Botany Division of DSIR at Lincoln. The drawing, published in Flora NZ II, p149, matches the Tararua drawings precisely. An undated drawing of a plant from Dansey Pass, Otago, clearly the same taxon, also shows the column wings much shorter than the anther. The fact that Matilda Smith's drawing, Plate 193 of Cheeseman's Illustrations of the New Zealand Flora Vol.II, matches very closely my own drawings is comforting. My concept of P. colensoi must surely be correct.

It was something of a shock to read in 1996 "Resolution of the Prasophyllum alpinum R.Br.
(Orchidaceae) complex in mainland south-eastern Australia, Tasmania and New Zealand" [1]
in which David Jones stated that Prasophyllum alpinum had column wings about half as long
as the anther, whereas the other three species discussed, (P. colensoi, P. tadgellianum and
P. sphacelatum), all had column wings as long as or longer than the anther. Could this be so?

It is conceivable that the specimens lodged by J.D.Hooker in support of his descriptions of
Prasophyllum colensoi [2]  do in fact have column wings as long as or longer than the anther.
Those specimens should supply the answer, but unfortunately no one specimen is designated
the "type".

Also it is conceivable that the Hooker specimens represent more than one taxon. Some may have column wings shorter than the anther; some may be as long as or longer. Jones wrote that the species would be lectotypified in a forthcoming publication. To do so would surely entail a critical examination of all eligible specimens. As they are now more than 150 years old, to do so would risk serious damage. The flowers are small and the columns would not normally be exposed.

If a lectotype is selected, it must agree (at least as well as all the other specimens) with Hooker's
original description, which states rather vaguely "column very short, with very low two-lobed
lateral pieces". It would seem irrational to interpret that as column wings as long as or longer
than the anther. I don't think I shall have to alter my concept of Prasophyllum colensoi Hook.f.

I think it likely, that from the specimens available to Jones to draw, (and to influence his description of P. colensoi), he selected a plant which outwardly resembled P. colensoi, but which had column wings about as tall as the anther. With almost any genus other than Prasophyllum, that difference might seem of little importance.

However in 1909, Dr R.S.Rogers, reviewing Prasophyllum in Australia, said - "The genus Prasophyllum is admittedly the most difficult and perplexing one in the whole of the Orchidaceae. Not only are the flowers frequently of very small size, but there are so many intermediate forms, that almost every species may be said to blend insensibly  into another" [3].  

Since reading Jones' paper, I have examined many flowers (mainly on the Volcanic Plateau) always finding that plants considered to be P. colensoi had column wings clearly shorter than the anther, until Anne Fraser drew my attention to slender plants with dark-purple stems, close to the lower end of the old Blyth Track, off Turoa Road above Ohakune. These had column wings nearly as long as the anther, on less uniformly coloured flowers. We tagged them Prasophyllum "A" [see Journals 75: pp 13-15: 79: pp8-10].

In subsequent seasons this P. colensoi look-alike adopted more varied colour patterns and
seemed far more plentiful than P. colensoi s.s. I presumed that this plant or something very
like it, might be the subject for Jones' drawing of P. colensoi.

A taller, slender-tepalled form, often growing in shallow water, also has column wings
approaching the anther in length, but is more clearly a separate taxon, because it has
ovate floral bracts with sub-acute apices, whereas the floral bracts of P. colensoi are
very blunt or truncated. We tag-named this form Prasophyllum "B". [see Journal 79: pp 8-10].  

I now think this form, rather than Prasophyllum "A" is the reason for Jones' misidentification.
Its tepal  lengths match more closely those  given in his description of P. colensoi.

This description [1], also includes characters which suggest Prasophyllum "B", but which were not mentioned  in Hooker's original description [2], such as: "floral bracts ovate….closely sheathing, sub-acute to obtuse or emarginate". Also of the lateral sepals Hooker's description stated "joined at the base", whereas Jones wrote "free or connate at the base". Again this suggests Prasophyllum "B". The lateral sepals of P. colensoi s.s. are probably never free, but are often connate for most of their length, occasionally almost to their apices.

Although I no longer suspect Prasophyllum "A" of being the cause of the confusion, I still regard
it as a separate taxon from P. colensoi s.s., perhaps a sub-species or variety. The diagnostic
characters separating them seem very minor. The only rather obvious difference is the very
wide rage of colours exhibited by Prasophyllum "A".

Forms "A" and "B" may not be the only ones at present included under P. colensoi. The column shown by Dorothy Cooper on p70 of her Field Guide to New Zealand Native Orchids shows the column wings clearly shorter than the anther, which equals the rostellum.

The pickled plant from Paranui collected by Doug McCrae [see Journal 89: p43] has column wings and anther equal in length. Whether they also equal the rostellum is unclear. This may of course be P. rogersii Rüpp. What other forms (particularly in the South Island) await discovery?

References

1: Jones D. Resolution of the Prasophyllum alpinum R.Br. (Orchidaceae) complex in mainland
    south-eastern Australia, Tasmania and New Zealand. Muelleria 9: pp51-62 (1996)
2: Hooker J.D. Flora novae-zelandiae 1: p241 (1853)
3: Rogers R.S. A critical review of South Australian  Prasophylla.Trans. Royal Society South Australia
    pp 197-222 (1909)