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A new location for the Poor Knights spleenwort ( Asplenium pauperequitum, Aspleniaceae) on The Forty Fours, Chatham Islands, New Zealand

A new location for the Poor Knights spleenwort ( Asplenium pauperequitum, Aspleniaceae) on The Forty Fours, Chatham Islands, New Zealand
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  Cameron et al.—   Asplenium pauperequitum  on The Forty Fours199    New Zealand Journal of Botany, 2006, Vol. 44 :   199–2090028–825X/06/4402–0199 © The Royal Society of New Zealand 2006  A new location for the Poor Knights spleenwort   (  Asplenium pauperequitum , Aspleniaceae) on The Forty Fours, Chatham Islands, New Zealand E. K. CAMERONAuckland War Memorial MuseumPrivate Bag 92018Auckland, New ZealandP. J. de LANGE*Terrestrial Conservation UnitDepartment of ConservationPrivate Bag 68908 NewtonAuckland, New ZealandL. R. PERRIEP. J. BROWNSEYMuseum of New Zealand Te Papa TongarewaPO Box 467Wellington, New ZealandH. J. CAMPBELLInstitute of Geological and Nuclear Sciences LimitedGracefield Research CentrePO Box 30368Lower Hutt, New ZealandG. A. TAYLOR Research, Development and InformationDepartment of ConservationPO Box 10420Wellington, New ZealandD. R. GIVEN†Botanical Services Curator Christchurch City CouncilPO Box 237Christchurch, New ZealandR. M. BELLINGHAMBethells RoadTe HengaAuckland, New Zealand *Author for correspondence.†Deceased 27 November 2005 Abstract Documentation is made of the discovery of the Poor Knights spleenwort, (  Asplenium pauper-equitum ) in a sample of vascular plant specimens collected from The Forty Fours. These islands are the easternmost outlier of the Chatham Islands archi- pelago. Hitherto this fern had been believed endemic to the Poor Knights Islands and Mokohinau Islands of the Hauraki Gulf, off eastern Northland, North Island, New Zealand. Frond and spore morphology together with chloroplast DNA sequences were used to confirm its identity. Whether this fern disjunction of some 1245 km is the result of vicariance or long-distance dispersal is discussed and long-distance dispersal of fern spores or whole sporangia is con-sidered most likely. Keywords Aspleniaceae;  Asplenium pauper-equitum ; biogeography; Poor Knights Islands; Chatham Islands; The Forty Fours; trn L- trn F and rbc L chloroplast DNA sequences; vicariance; long distance dispersal; New Zealand flora INTRODUCTION  Asplenium pauperequitum  Brownsey et P.J.Jacks. (Aspleniaceae) is an uncommon and threatened fern endemic to the Poor Knights Islands and Mo-kohinau Islands, in the northern Hauraki Gulf, east of the Northland Peninsula of the North Island of  New Zealand (Brownsey & Jackson 1984; Cameron 1993; de Lange & Cameron 1999; de Lange et al. 2004) (Fig. 1A). The species was first gathered on the Poor Knights in 1970 (Parris 1990) but was not made known to science until it was rediscovered during a weed survey of the Poor Knights Islands in 1982 and subsequently described (Brownsey & Jackson 1984). At the time of its formal description it was considered to have no obvious affinity to any other New Zealand species of the genus. However, it was suggested that it might be of tropical srcin, and have some relationship to the  A. polyodon ag-gregate, a group with which it shares the same dark red-brown stipe and rachis and long, narrow rhizome  B05044; Online publication date 4 May 2006  Received 5 October 2005; accepted 15 February 2006    New Zealand Journal of Botany, 2006, Vol. 44200 Fig. 1 Distribution of  Asplenium pauperequitum  based on herbarium specimens. A , the New Zealand subcontinent, showing location of the Poor Knights and Mokohinau Islands in relation to The Forty Fours; B , the Chatham Islands showing exact location of The Forty Fours. scales (Brownsey & Jackson 1984). It was also suggested that the apparent lack of close relatives in the Pacific region argued against a recent srcin from that area, and that because of its octoploid chromosome number it was probably an endemic of polyploid srcin. Recently, Perrie & Brownsey (2005) used chlo-roplast DNA sequence data to place  A. pauperequi-tum  as sister to  A. flabellifolium  Cav. However, they observed that the relationship is not especially close, and that further sampling of Pacific taxa may ultimately find species with greater affinity to the octoploid  A. pauperequitum , and possibly even its tetraploid progenitor or progenitors. Whatever its srcins and relationships to oth-er  Asplenium species,  A. pauperequitum  has the dubious honour of being one of the most threat-ened endemic New Zealand ferns (de Lange et al. 2004). The species is apparently extinct on the Mokohinau Islands (Cameron 1993; de Lange & Cameron 1999), while on the Poor Knights Islands  populations fluctuate widely from year to year. Although this may be a natural facet of its ecology,  populations have also declined due to introduced animal pests, and possibly to over-collection by  botanists in the past (de Lange 1994). The species has not yet been successfully cultivated. Because of its high threat status (“Acutely Threatened/Nation-ally Endangered CD, EF, HI, OL, IE ”; de Lange et al. 2004,  p. 55) and presumed distribution, field botanists have searched for it in other northern archipelagos, to date without success.  Cameron et al.—   Asplenium pauperequitum  on The Forty Fours201 Fig. 2 The Forty Fours (Motuhara), the easternmost of the Chatham Island group. A NEW LOCATION FOR  ASPLENIUM  PAUPEREQUITUM  It came as a considerable shock when  A. pauper-equitum  was identified within a sample of plant specimens collected in January 2005 on the main island of the Forty Fours, Motuhara, an extremely isolated, easterly outlier of the Chatham Islands, c.1245 km south-south-east of the Poor Knights Is-lands. The Forty Fours (Fig. 1B, 2–4) (43 ° 57′48″S, 175 ° 50′12″W) are the easternmost extension of the Chatham Islands archipelago and also of the New Zealand subcontinent. They are a cluster comprising one large (Motuhara), east-west aligned, flat-topped, elongated island (600 m long, 60 m a.s.l.) and five steep-sided stacks (Andrews et al. 1978). They are extremely remote and rarely visited, except by Cha-tham Islanders who fish the waters nearby but rarely, if ever, land (R. Goomes pers. comm.). The islands are composed of Mesozoic-aged, hard, metamor- phosed, sparsely stratified feldsarenite sandstone, corresponding to the “Matarakau Greywacke”of Chatham Island and the Torlesse terrane of New Zea-land (Andrews et al. 1978). They are believed to have  been exposed for about 4 million years. Motuhara is sparsely vegetated (Fig. 3), mainly with  Leptinella  featherstonii F.Muell. (corresponding to the form  previously known as Cotula renwickii  Cockayne), and occasional patches of  Lepidium  aff. oleraceum  (the variant recognised as  L . aff. oleraceum  (a) by de Lange et al. 2004) and  Atriplex buchananii  (Kirk) Cheeseman, and is a significant breeding ground for the northern royal albatross (  Diomedea sanfordi ) (Fig. 4) and Pacific mollymawk ( Thalassarche  sp. nov.) (Aikman & Miskelly 2004). Along with most of the outer islets of the Chatham Islands, and with the notable exception of bird life, their biota has never been thoroughly documented. Therefore, as  part of a wider study of the geology and biota of these remote islands by the Chathams Emergent Ark Research Survey (CHeARS) team, three of us (RMB, HJC, DRG) participated in a visit to the Forty Fours on 27 January 2005. During the visit eight species of vascular plants were collected which were subsequently forwarded to the Auckland Museum for identification. It was amongst this gathering that PdL and EKC recog-nised specimens of  Asplenium    pauperequitum  (AK 290307; Fig. 5). Only one patch was found under  plants of the Chatham Islands endemic button daisy,  Leptinella featherstonii , in a deep crevice, near the summit of the island (Fig. 4). CONFIRMATION OF IDENTITY Although the initial examination of the specimens suggested that they belonged to  A. pauperequitum , such an unexpected locality and large disjunction of c. 1245 km south-south-east from the Poor Knights Islands required further confirmation. The collec-tion was sent to the herbarium at Museum of New Zealand Te Papa Tongarewa (WELT) for critical examination by the principal describing author of   New Zealand Journal of Botany, 2006, Vol. 44202 Fig. 3 Upper slopes of the main island of The Forty Fours, Motuhara. the species (PJB) and also for molecular analysis (LRP). The morphological analysis confirmed the identification with regard to frond, stipe, scale mor- phology, and spore size, shape, and ornamentation. The only major departures from the range exhibited  by Poor Knights plants of this species were that some fronds were more divided and slightly less glossy. Using the methods of Perrie & Brownsey (2005) and Perrie et al. (2005), DNA was extracted and chloroplast sequences were obtained from two mor- phologically separate fronds from the Forty Fours collection (AK 290307). These were the larger frond in the cellophane packet and the frond mounted in the centre of the sheet. DNA from the “cellophane” frond was of high quality, and yielded a nearly com- plete sequence of the trn L- trn F intergenic spacer and the rbc L gene (GenBank DQ186547 and DQ186550, respectively). A complete trn L- trn F intergenic spac-er sequence was obtained from the “central” frond (DQ186548), but because of its lower quality of DNA, only 215 base-pairs (between the primers rbc LAsF2 and rbc LAsR2) could be generated for rbc L   (DQ186551). Independent PCR products were sequenced as a guard against polymerase errors. These extractions and PCRs were performed in a laboratory in which PCR of these loci in  Asplenium  had not previously been undertaken. The trn L- trn F and complete rbc L sequences from the “cellophane” frond from AK 290307 were compared with previously published data from a selected subset of taxa (Perrie & Brownsey 2005; Schneider et al. 2005; with taxonomic authorities and GenBank numbers therein). Also included was a new rbc L sequence (GenBank DQ186552) for a sample of  A. chathamense  (WELT P20498) from which trn L- trn F data had been previously reported (Perrie & Brownsey 2005). Phylogenetic analyses using maximum parsimony, maximum likelihood, and a Bayesian approach (see Perrie et al. (2005) for details of methods), with the loci investigated separately or together, were completely congruent  Cameron et al.—   Asplenium pauperequitum  on The Forty Fours203 Fig. 4  The summit area of Motuhara showing the main vegetation type on the island, dominated by  Leptinella    feath-erstonii , and numerous northern royal albatross (  Diomedea sanfordi ). It was in this approximate area that  Asplenium    pauperequitum  was discovered. in placing the Forty Fours material as sister to Poor Knights Islands  Asplenium pauperequitum , with this being strongly supported. Sister to them was  A. flabellifolium ; no known sequences are more closely related to  A. pauperequitum  than those of  A. flabellifolium  (LRP unpubl. data). A summary of these analyses is presented in Fig. 6. The partial sequences from the “central” frond differ from those of the “cellophane” frond, indi-cating that at least two individuals are represented on the sheet AK 290307. Further, as indicated in Table 1, both are different from the Poor Knights sample analysed by Perrie & Brownsey (2005) and from additional Poor Knights material for which data are reported here (WELT P020894; GenBank rbc L DQ186553, trn L- trn F DQ186548). Genetic variation is clearly present between and within both  populations, but a detailed comparison awaits ad-ditional data. DISCUSSION This discovery rates alongside other such nota- ble plant disjunctions as  Leucopogon    parviflorus  (Andres) Lindl. (de Lange et al. 2003),  Kirkianella   novae-zelandiae  f.  glauca  Allan (Dopson et al. 1999) and  Metrosideros parkinsonii  Buchanan (Allan 1961; Atkinson et al. 1962), as perhaps one of the more extreme examples of a New Zealand vascular plant disjunction yet recorded. However, now that the identification of the Forty Fours  A. pauperequitum  collection has been resolved, we are faced with the obvious question: how did this disjunct distribu-tion arise? There are three possible answers: 1, the species was introduced by humans; 2, it has a relict vicariant distribution and/or has been previously overlooked or died out from locations between the currently known occurrences; or 3, the occurrence is an example of long-distance dispersal.
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