In 2005 whilst at the Allan Herbarium (CHR), Lincoln I happened to ask Dr David Glenny if anyone had examined the liverwort flora of the Chatham Islands? David told me that a few people had collected liverworts from there, including him in 1997, and so far found "nothing special". Intrigued, I then asked if David would like me to collect hornworts and liverworts while doing vascular plant work over there, and he agreed that this would be a good idea. David also kindly gave me a checklist of the hornworts and liverworts known to be on the island, and further, he agreed to identify what I got from there.
David's initial listing for the islands suggested that despite the group's large size (c.100, 000 ha) it had very little to offer, with only 92 taxa recorded. None of these were endemic - which struck me as odd, considering the presence of 37 or so named vascular plant endemics (including two endemic genera), one endemic moss (Macromitrium ramsayae), and one lichen (Caloplaca maculata). This being the case, surely there had to be an endemic liverwort out there as well? David admitted that this was quite likely but, when considering the apparently depauperate liverwort flora, he surmised that perhaps the island group's extreme modification may already have eliminated most of the diversity and, if so, any likely endemics, and that this coupled with the group's isolation from New Zealand, probably accounted for the low species diversity. These are good points but, nevertheless, I noted that David's field work there had been limited to Rekohu (Chatham Island), the largest of the islands in the group, and, because he used bicycles to get around and did not know many of the landowners (most of the land on the islands is privately owned), his visits were necessarily limited to the few reserves he could easily and legally explore. So, up for a challenge I devoted what time I could during five 10-day long visits to the islands between January 2006 and November 2008 to collecting hornworts, liverworts, and also, for Dr(s) Allan Fife and Jessica Beever, mosses.
As of 2011, we now know that there are nearly 300 hornwort and liverwort taxa on the islands (already quite a jump from the 262 reported by Glenny & de Lange 2008). However, obtaining exact numbers is not that easy, as many of the genera and families I collected are still being studied, mostly by Dr(s) John Engel (Lophocoleaceae, Plagiochilaceae) and Matt von Konrat (Frullaniaceae) at the Field Museum, Chicago and Dr Matt Renner (Lejeuneaceae) at NSW Herbarium, Sydney. At some stage, the finds will be made known in a paper we are slowly writing about the Chatham Islands Hepaticae.
As such, it was very pleasing that, in May 2009, John Engel wrote to me to enquire about a Plagiochila I had collected with Peter Heenan from the southern shores of Lake Rakeinui, on Rekohu. Rakeinui is the largest of the peat lakes on the southern tablelands, and luckily most of it is now protected within a massive southern tablelands conservation covenant. The lake itself is beautiful, a true peat lake with its water stained darker than coffee. The lake broods black and inky in a deep depression fringed by dense tarahinau (Dracophyllum arboreum) / matipo (Myrsine chathamica) forest. The shoreline is home to the largest known population of the threatened Chatham Islands toetoe (Cortaderia turbaria) on Rekohu, and the murky waters of the lake are home to the endemic Chatham Island mudfish (Neochanna rekohua). Access to the lake is not so much difficult as tedious, involving a long day's driving, then 4-wheel driving, then quad biking and then - finally - walking several kilometres across Sporadanthus - Olearia - Dracophyllum bog and valleys and ridgelines choked in dense tarahinau/matipo forest. Once the lake is reached you can't actually see it, and to find it you have to plunge down a series of forested cliffs until, like magic the lake suddenly comes into view. I also have found that, for some reason, whenever I go there it either snows or rains (or - to be different - it does both).
In September 2007, when we gathered the Plagiochila that John Engel was interested in, Peter Heenan, local Department of Conservation Ranger (and Chatham Islander) Denny Prendeville, and I were slogging and wading around the flooded lake margin collecting toetoe for an AFLP DNA finger printing study to ascertain that species' overall genetic diversity. It was sleeting, we were already very wet and cold and not really that happy. Having fallen in the lake twice already, I was perhaps the least happy of the three, though whilst wringing out my sodden clothes I had the prescience of mind to collect a handful of a Plagiochila growing on the forest floor above the lake. I determined this as yet more Plagiochila obscura (a very common species on the islands) and thought nothing of it. Nor did David Glenny who later examined the material in New Zealand, you see P. obscura is a very uniform and common species throughout New Zealand (Fig. 1). Yet, as we all should know, looks can be deceiving....
So turning the clock forward to 2009, John Engel, as part of his revision of the Plagiochilaceae for the next volume of the New Zealand Liverwort Flora (see Engel & Glenny 2008), had undertaken a routine interloan of specimens from that family from New Zealand herbaria. In the process, the Lake Rakeinui gathering of P. obscura (e.g., P.J. de Lange CH1230 & P.B. Heenan, AK 302646) caught John's eye because of the distinctive toothing of the dorsal margin of the foliage leaves, which in this gathering were toothed along the base rather than, as is typical of this species elsewhere in New Zealand (and on the Chatham Islands), the distal portion of the leaves. Further, the male bracts were sharply acute rather than deeply toothed. John decided that this gathering did not match anything else on the Chatham Islands or elsewhere in New Zealand for that matter, and that it deserved recognition as a new variety. In the process, John and Gary Smith Merrill had also ascertained that Plagiochila obscura had been used incorrectly in New Zealand, they showed that this name was in fact a synonym of another New Zealand species, P. stephensoniana. That being the case, it meant that those plants that we had been (incorrectly) calling P. obscura should now be known by the next available name, P. arbuscula (see Engel & Smith Merril 2010).
The Lake Rakeinui Plagiochila has now been described as P. arbuscula var. rekohuensis, the varietal epithet chosen specifically to honour the Moriori whose name for Chatham Island is "Rekohu" (Moriori being the indigenous people of that island group (King 1989)). This liverwort is not only new to New Zealand but it is the first endemic liverwort to be recognised from the islands (cf. Glenny & de Lange 2008). Interestingly, late last year John made further inquiries about a Heteroscyphus I had collected from the sea cliffs north of Waipaua Stream, Rangiauria (Pitt Island) because that too is also distinct, warrants formal description and will be recognised as another endemic to the islands.
The results are pleasing because they remove the past botanical anomaly of the islands. The absence of an endemic liverwort from the Chatham's simply made no sense, especially when one considers that the much smaller and geologically younger Raoul Island supports at least two endemic liverworts (Plagiochila pacifica and Radula cordiloba subsp. erigens) (Renner & de Lange in press). The Chathams had to have at least one, and now it has two, and perhaps more yet to follow as John Engel, Matt von Konrat and Matt Renner work over the other gatherings they have on loan.
I would like to especially thank John Engel for his interest in the Chatham Island liverwort gatherings I have made, and his freely given comments and insights into his ongoing work for the New Zealand Liverwort Flora series. I thank David Glenny, John Braggins, Matt Renner and Matt von Konrat for their help with working over the collections I have made from the Chatham Islands and their identifications, and David especially for providing his initial checklist in 2005 to form my starting point. On the Chatham Islands, I remain indebted to the Department of Conservation Area staff at Te One (Rekohu) and on Rangiauria, especially Amanda Baird, Bridget Gibb, Denny Prendeville, Kenny Dix, Ken Hunt and Maria Pascoe for field assistance, transport, accommodation, sorting out boats and of course, access across private land. I also thank John Sawyer (January 2006), Peter Heenan (February 2006, September 2007, May 2008, November 2008), Rob Smissen (February 2006) and Gary Houliston (May 2008) for their interest in my work and their participation and company in the field.
Engel, J.J.; Glenny, D. 2008: A Flora of the Liverworts and Hornworts of New Zealand. Vol. 1. St Louis, Missouri Botanical Garden Press.