ARTICLE : A comment on Wahlenbergia littoricola subsp. vernicosa

 A comment on Wahlenbergia littoricola subsp. vernicosa

Petterson (2005) provides a summary of her 1997 revision of Wahlenbergia published in the New Zealand Journal of Botany.   Her article is both useful and an excellent example of “science transfer” to the masses.   However, I feel the need to clarify the misleading remarks made over my admittedly senior but still joint decision on the taxonomic status of W. vernicosa J.A.Pett., viz “P.J. de Lange [sic] prefers to call this species W. littoricola Smith (1992) [sic], but I am not convinced, as the habitat and the foliage as described by Smith (pp. 140-141) are at odds … ”.   This does not explain the decision taken by the de Lange & Cameron (1999) rather it ignores points we made and the conclusions we reached in our treatment of W. vernicosa J.A.Pett.

What Petterson is alluding to is that Ewen Cameron and I made a new combination for W. vernicosa within W. littoricola P.J.Sm., at the rank of subspecies i.e., W. littoricola subsp. vernicosa (J.A.Pett.) de Lange et E.K. Cameron (de Lange & Cameron 1999: 435).   The basis for this change in rank is given by de Lange & Cameron (1999: 435) where it is explained that the decision to make this combination at that rank was based on our examination of material held of both taxa at the Auckland Museum (AK), Allan Herbarium (CHR) and New South Wales (NSW) herbaria which did not, in our view, support species rank.   Specifically we felt that Petterson’s W. vernicosa matched W. littoricola very closely with regard to “their growth habit, few to many, heavily branched stems, flowers borne in complex thyrsoids, with the corolla shortly campanulate, and the stigma constricted at one third to two-thirds down from the stigmatic lobes”.   Furthermore the capsules of both species are obconic, they have comparable ecologies and they share the same chromosome number (2n = 54) otherwise unknown from the New Zealand species of the genus.   Also, we had sent New Zealand specimens to the author of W. littoricola, Peter Smith, who after careful consideration stated (in litt.) that “the only significant character distinguishing New Zealand plants from those in Australia is the consistently glossy leaf surface of New Zealand specimens”.   Because both taxa seem to be allopatric, yet the glossy leaf was a consistent difference between them, and Smith (in litt.) felt this was important; we reduced W. vernicosa to the rank of subspecies.

Note of course that there is no requirement for people to follow our decision because in effect, there are now two names at two ranks, species or subspecies for the same entity, and people can use whatever name they wish.   They can even, as Webb & Simpson (2001) have done, ignore them altogether and refer these taxa along with W. akaroa J.A.Pett., W. rupestris G. Simpson, W. ramosa G. Simpson, W. violacea J.A. Pett. back to the earliest name available W. gracilis (G.Forst.) Schrad. which is the “parent” taxon from which these other taxa were later segregated (Petterson 1997).   The choice is yours.

Petterson (2005) also repeats her 1997 suggestion (loc. cit.) that W. vernicosa (W. littoricola subsp. vernicosa) might be the same as the Lord Howe Island endemic W. insulai-howei Lothian.   Although I cannot be certain, because, like Petterson I have not seen that species in the wild, herbarium specimens that I have examined at NSW! at WELT! and WELTU!, show that W. insulai-howei has a different growth habit viz, “tufted and spreading, terminating in single, usually unbranched stems … leaves are usually crowded into basal rosettes … flowers solitary, or 2 - 3 per stem, deeply campanulate, with the style constricted at half the length down from the stigmatic lobes, and the capsules … hemispherical to short obconic” (de Lange & Cameron 1999: 435).   These characters are not present in N.Z. specimens of W. littoricola subsp. vernicosa that I have seen, and it is perhaps noteworthy that the last author to revise the Australian taxa – Peter Smith, did not see fit to suggest that the New Zealand plants we had sent him should be placed there either.   So I find it peculiar then, that Petterson (2005) adds nothing further to her earlier published remarks, but chooses to ignore rather than refute our comments on her earlier speculation.

Regarding distribution I cannot confirm the statement attributed to me (Petterson 2005: 17) that it is in Tasmania, though I have seen and collected plants from there that suggest it might be.   I would have liked to have seen some resolution on the enigmatic statements made by Petterson (1997) that W. vernicosa (W. littoricola subsp. vernicosa) is a New Zealand endemic but also apparently present in Tonga.   Irrespective, events have now overtaken this issue because W. littoricola subsp. vernicosa is present on Norfolk Island, where it is regarded as native, and so it is clearly indigenous to New Zealand (de Lange et al. 2005).

Otherwise I can see little point in debating over such variable characters raised by Petterson (2005) to assert the distinctiveness of W. littoricola from her W. vernicosa (W. littoricola subsp. vernicosa) such as consistency of flower colour (it varies in Australian subsp. littoricola as well I can assure you), ecology (both grow near the coast and both grow inland, besides which the species epithet “ littoricola” means “dwelling near the sea”), leaf phyllotaxis (which is rather variable in both subspecies), or defining a consistent measurable range for “shortly campanulate”, “campanulate” or “deeply campanulate”, characters in my experience can vary on the same plant.   The point is that Petterson is entitled to her views and I mine but the reasoning behind taxonomic decisions should, indeed must, be elaborated so that others can form their own opinions.

Ultimately in defence of both assessments I think that it cannot be denied that New Zealand Wahlenbergia, as indeed Smith (1992) himself had admitted for the Australian species, are a difficult group.   They are poorly collected, key diagnostic characters are difficult to preserve or often missing, flower colours fade over time (or change from white to blue and blue to white!), and the flowers and fruits are targeted by insects unless carefully curated.   Considering these problems I strongly maintain that Petterson (1997) provided a truly remarkable revision, bringing together years of careful and patient study of plants in the wild and in her garden.   Nevertheless her work is still primarily based on morphological characters supplemented with some chromosomal and ecological evidence.   In this day and age, with such difficult genera, such revisions should be augmented with any number of the wealth of other technologies now available that can help resolve such problem groups.   In particular, I see a need to further test Petterson’s taxa using a much wider sampling and key molecular markers.

Peter J. de Lange

References

de Lange, P.J.; Cameron, E.K. 1999:   The vascular flora of Aorangi Island, Poor Knights Islands, northern New Zealand.   New Zealand Journal of Botany 37: 433 - 468.

de Lange, P.J.; Gardner, R.O.; Crowcroft, G.M.; Stalker, F.; Cameron, E.K.; Braggins, J.E; Christian, M.L. 2005:   New records and additions to the flora of Norfolk Island, South Pacific.   New Zealand Journal of Botany 43: 563-596.

Petterson, J. 2005:   The genus Wahlenbergia, (Campanulaceae): the harebells of New Zealand.   Wellington Botanical Society Bulletin 49: 16 - 35.

Petterson, J.A. 1997:   Revision of the genus Wahlenbergia (Campanulaceae) in new Zealand.   New Zealand Journal of Botany 35: 9 - 54.

Smith, P.J. 1992:   A revision of the genus Wahlenbergia (Campanulaceae) in Australia.   Telopea 5: 91 - 175.

Webb, C.J.; Simpson, M.J.A. 2001:   Seeds of New Zealand Gymnosperms and Dicotyledons.   Christchurch, Manuka Press.