Analysis of Microfossils in Archaeological Deposits from Two Remote Archipelagos: The , Eastern Micronesia, and the Pitcairn Group, Southeast Polynesia1

Mark Horrocks2,3,5 and Marshall I. Weisler4

Abstract: Pollen and starch residue analyses were conducted on 24 sediment samples from archaeological sites on Maloelap and Ebon in the Marshall Islands, eastern Micronesia, and Henderson and Pitcairn Islands in the Pitcairn Group, Southeast Polynesia. The sampled islands, two of which are ‘‘mystery islands’’ (Henderson and Pitcairn), previously occupied and abandoned before European contact, comprise three types of Pacific islands: low coral atolls, raised atolls, and volcanic islands. Pollen, starch grains, calcium oxylate crystals, and xylem cells of introduced non-Colocasia (aroids) were identified in the Marshalls and Henderson (ca. 1,900 yr B.P. and 1,200 yr B.P. at the earliest, re- spectively). The data provide direct evidence of prehistoric horticulture in those islands and initial fossil pollen sequences from Pitcairn Island. Combined with previous studies, the data also indicate a horticultural system on Henderson comprising both field and tree crops, with seven different cultigens, including at least two species of the Araceae. Starch grains and xylem cells of Ipomoea sp., possibly introduced I. batatas, were identified in Pitcairn Island deposits dated to the last few centuries before European contact in 1790.

During the late Holocene settlement of This involved starch staples produced the eastern Pacific, agricultural practices com- through a variety of ‘‘wet’’ and ‘‘dry’’ field- bining tropical Asian-Pacific and American cropping methods (Kirch 1994) and tree crops were adapted to a diversity of island cropping (Yen 1973). The extension of these environments (Yen 1973, Spriggs 1982, Ayres practices to remote islands of often very small and Haun 1990, Kirch 1994, Bellwood 2005). area with barren soil, unreliable groundwater supply, unpredictable rainfall, and frequent marine inundation was one of the most chal- 1 The Marsden Fund administered by the Royal Soci- lenging accomplishments of this diaspora. ety of New Zealand provided support for M.H. Funding from the Wenner Gren Foundation for Anthropological The starch staples include four species of Research, the United Nations, the U.S. National Park the Araceae, Colocasia esculenta (), Alocasia Service, the Australian South Pacific Cultures Fund, and macrorrhiza (elephant ear taro), the Historic Preservation Office (Republic of the Mar- merkusii (syn. chamissonis, giant swamp taro), shall Islands) provided support for M.I.W. Manuscript accepted 2 June 2005. and Amorphophallus paeoniifolius (elephant 2 Microfossil Research Ltd., 31 Mont Le Grand Road, yam); and Dioscorea spp. (yams), Musa spp. Mount Eden, Auckland 1003, New Zealand (e-mail: (bananas), Artocarpus altilis (breadfruit), and www.microfossilresearch.com). Ipomoea batatas (sweet potato). In total, there 3 School of Geography and Environmental Science, are approximately 30 species of subsistence University of Auckland, Private Bag 92-019, Auckland, New Zealand. listed (see, e.g., Kirch 1989, Loy et al. 4 School of Social Science, University of Queensland, 1992, Matthews 1996). Many of these origi- St. Lucia 4072, Queensland, Australia. nated in Asia and, recent research suggests, 5 Corresponding author. also in the Sahul continental region (Haberle 1995, Lebot 1999, Denham et al. 2003, Mat- Pacific Science (2006), vol. 60, no. 2:261–280 thews 2003, Bellwood 2005). They were in- : 2006 by University of Hawai‘i Press troduced throughout the Pacific by early All rights reserved human colonizers. Ipomoea batatas (sweet

261 262 PACIFIC SCIENCE . April 2006 potato) and Lagenaria siceraria (bottle gourd) this growing body of evidence, however, ma- originated in South America, their introduc- jor gaps in the Pacific record remain. In addi- tions a result of Polynesian contact (Hather tion, human settlement of atolls is extremely and Kirch 1991, Green 2000). underresearched (Weisler 1999). Research on the age, development, and di- Although ethnographic accounts are valu- versity of early agriculture in the Pacific has able sources of information, we would like to been hindered by transformation of tradi- know which species were introduced where tional cropping systems after European con- and when. The so-called ‘‘mystery islands’’ tact and archaeological scarcity of crop are particularly problematic in this respect fossils. However, recent advances have been because they were uninhabited at the time made with regard to the latter at sites across of Western contact. There are more than a the Pacific by the identification of plant mac- score of these, typically small targets at some rofossils and especially by the application of a distance from their nearest neighbors (Irwin range of microfossil techniques, namely pol- 1992). Given the isolation, small size, and len, starch residues, and phytoliths. In Micro- especially resource-poor nature of these hab- nesia, prehistoric pollen (and macrofossils) of itats (including low-nutrient soils and unpre- the Araceae and Artocarpus altilis has been re- dictable water resources), it is uncertain if ported in the Mariana, Caroline, and Mar- horticulture was practiced at all. shall Islands (Beardsley 1994, Athens et al. During an archaeological expedition to the 1996, Athens and Ward 2002, 2004). In Mel- Pitcairn Group in Southeast Polynesia in anesia, Araceae starch residues have been 1991–1992, sediment samples from deposits identified at Lapita settlements in the Bis- thought to be prehistoric gardening areas marck Archipelago (Crowther 2005) and were collected (Weisler 1995). The project (Horrocks and Bedford 2005). Simi- was investigating the survival of small human larly, Lentfer and Green (2004) identified groups on isolated, marginal landfalls, and an Musa phytoliths at a Lapita site in the Bis- island-wide archaeological survey and exten- marcks. In Polynesia, starch residues, phyto- sive excavations in habitation sites were con- liths, and pollen of a suite of introduced ducted (Weisler 1995, 1997). In another cultivated plants have been identified in New project samples were collected in 1993–1997 Zealand, comprising Ipomoea batatas, Colocasia from the Marshall Islands in eastern Micro- esculenta, Lagenaria siceraria, and Broussonetia nesia (Weisler 1999, 2001a). That project papyrifera (paper mulberry) (Horrocks was investigating the timing and nature of 2004a). In the Society Islands, Parkes (1997) Araceae horticulture across the rainfall gradi- reported pollen of Ipomoea batatas, Colocasia ent in the Marshalls. Extreme remoteness is esculenta, and Cordyline fruticosa (syn. termina- a common feature of these two distant archi- lis, Pacific Island cabbage tree). Athens pelagoes. The sites presented the opportunity and Ward (1997) reported pollen of Colocasia to test different tropical soil types in a range esculenta, Cordyline fruticosa, and Aleurites mo- of environmental settings for preservation luccana (candlenut tree) in Hawai‘i, and Cum- of plant microfossils and to look for direct mings (1998) reported pollen of Ipomoea evidence of prehistoric horticulture near the batatas and starch granules of Colocasia on outer margins of both Polynesia and Micro- Easter Island. Macrofossils identified in Poly- nesia. The outer Pacific archipelagoes were nesia include Ipomoea batatas root (commonly among the last habitable places on Earth to referred to as tuber) from Hawai‘i (Rosendahl be colonized by people. These islands are and Yen 1971), the (Hather and ecologically fragile and often small, providing Kirch 1991), and New Zealand (e.g., Yen microcosms for the study of human adapta- and Head 1993); Aleurites moluccana endocarp tion to diverse, extreme environments. Pre- from the Cooks and Henderson Island (Kirch sented here are results of recent analyses of et al. 1992, Weisler 1995); and Araceae and pollen and starch residues in the sediment Musa leaf also from Henderson (Weisler samples from archaeological sites in these ar- 1997, Hather and Weisler 2000). Despite chipelagoes. Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 263

The Study Areas, Sites, and Sample Context stratigraphically below a 1,580 G 80 yr B.P. date (Beta-69516 [Weisler 2001a]). The pit, marshall islands. Situated in eastern 73 cm in diameter, had subparallel sides to a Micronesia, the Marshall Islands comprise depth of 54 cm. Sample 3 is from MLMl-3, 29 atolls and five coral islands without a TP19, 21, and 24, buried A horizon dating central lagoon aligned in two roughly parallel to 1,910 G 70 yr B.P. (Beta-79576 [Weisler alignments. The climate is tropical, with the 1999]). Because the buried A horizon was archipelago traversing a rainfall gradient thin, sediment was taken from the sidewall from @1,000 mm in the north to @4,000 of three contiguous test pits. This sample is mm in the south. Mean annual temperature associated with the construction of an adja- is @27 C. Most of the atolls and islands are cent pit currently used for cultivation of currently inhabited; the two northernmost Cyrtosperma merkusi. and driest atolls, Taongi (Pokak) and Bikar, The Ebon and Enilok islet (Ebon ) are uninhabited but are visited occasionally samples comprise samples 4–8. Samples 4–7 to collect birds and turtles. Samples from are from MLEb-2I, TP2 layers I, II, III, and two atolls were analyzed in this study: Maloe- IV, which correspond to samples 4–7 (Figure lap in the center of the archipelago and Ebon 1A). A 4-m-long trench was excavated in the far south. The 71 islets composing Ma- through the rim of a suspected horticultural loelap Atoll have a total terrestrial area of 9.8 pit, and stratigraphic samples were taken km2. Samples from one of these islets, Kaven from all four layers; layer III was the buried (2.3 km2), were analyzed. The 22 islets of A horizon dated to 1,930 G 40 yr B.P. (Beta- Ebon Atoll total 5.6 km2. Samples from two 92123 [Weisler 2002a]), layer I the near- of these, the largest, Ebon (2.7 km2), and surface A horizon, layer II a prehistoric habi- Enilok (0.4 km2), were analyzed. Low coral tation layer, and layer IV the sterile subsoil. atolls such as the Marshalls, usually only ca. Sample 8 is from MLEb-38, TP2, 65 cmbs 2–3 m above sea level, are prone to marine within a large pit feature measuring at least inundation during storms. Soils are typically 132 cm wide and @33 cm deep, below a date humus-poor and porous, with potable subter- of 1,560 G 70 yr B.P. (Beta-92134 [Weisler ranean water restricted to the largest islets of 2002a]). an atoll. Radiocarbon evidence suggests occu- pitcairn group. The Pitcairn Group, pation from ca. 2,000 yr B.P. (Weisler 1999). located in Southeast Polynesia, comprises the Detailed site descriptions and stratigraphic raised coral island of Henderson, two coral context are given in Weisler (2001a, 2002a). atolls (Oeno and Ducie), and the Pleistocene All samples are from prehistoric habitation volcanic island of Pitcairn. Only Pitcairn or suspected horticultural areas (see Appen- Island is currently inhabited. The climate dix). The Kaven islet (Maloelap Atoll) sam- is subtropical, with meteorological records ples comprise samples 1–3. Samples 1 and 2 from Pitcairn showing a mean annual rainfall are from MLMl-3, TP9, feature 1, a sus- of 1,716 mm but with considerable inter- pected storage pit for Artocarpus altilis (bread- annual variability, and a mean annual temper- fruit) paste. Small pits, <1 m wide and ature of @21 C (Spencer 1995). Samples @0.5 m deep (Weisler 2001b), were often from Henderson and Pitcairn Islands, both used to store Artocarpus paste to extend the ‘‘mystery islands’’ and therefore uninhabited availability of this seasonal crop. Especially at European contact, were analyzed in this on drought-prone islands, food storage was study. Soils throughout Henderson (37.2 an important buffer against famine, a strategy km2), as on low atolls, are humus-poor, po- well documented in the Marquesas Islands rous, and undeveloped, although at 30 m (Handy 1923, Linton 1925). Our Marshall Is- above sea level, the island is not subject to in- lands sample 1 from Kaven islet (Maloelap undation. Potable water is found as cave drips Atoll) was taken from inside the pit and following ample rains. Radiocarbon dating of sample 2 outside the pit, both at 53 cmbs all major habitation sites suggests a 600-yr (centimeters below surface). The samples are Polynesian occupation sequence commencing 264 PACIFIC SCIENCE . April 2006

Figure 1. Sampled profiles from the Marshall Islands and Henderson Island in the Pitcairn Group. Sample numbers and positions are shown in boxes (see Appendix for descriptions). A, North profile of MLEb-2I trench, Ebon Islet, Ebon Atoll, Marshall Islands (from Weisler 2002a). The darkened layer III is a buried A horizon. B, A typical profile (TP1 North profile) showing the suspected gardening layer at site HEN-23, Henderson Island.

1,100 yr B.P. (Weisler 1995). Suspected The sample areas consist of soil pockets, up horticultural soils in the northern and north- to 3 m across, between bedrock outcrops and eastern part of the island are associated with stone mounds. The archaeology of Hender- relic stands of the Polynesian introduced son Island is discussed by Weisler (1995, shrub Cordyline fruticosa and were sampled. 1997, 1998). Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 265

Pitcairn Island (4.5 km2) is much smaller layers II–IV are colluvial with minor amounts than Henderson, although it is higher (ca. of dispersed macroscopic charcoal, layer V is 330 m) with well-developed soils and a a cultural deposit, layer VI has minor greater variety of habitats. There are few amounts of dispersed charcoal, and layer VII springs on Pitcairn, and water flows down has no macroscopic charcoal. some of the valleys after rain. Radiocarbon evidence from Pitcairn is minimal, but occu- materials and methods pation should be similar to that at Henderson at ca. 1,100 yr B.P.; the earliest date associ- A total of 24 sediment samples, eight from ated with human activity is 615 G 105 yr the Marshall Islands (samples 1–8), five from B.P. (Weisler 1995). Two soil profiles were Henderson Island (9–13), and the remainder sampled on Pitcairn. The first comprised (14–24) from Pitcairn Island, were taken stratigraphic samples taken from the east side directly from sections and examined for evi- of a small drainage at Down Fence (8 m from dence of plant microfossils (pollen and starch a walking track and bridge), thought to be the residues). Descriptions and provenance of the result of landscape disturbance upslope on samples are given in the Appendix. Starch the plateau, the main gardening area today. residue analysis was carried out on all sam- The second profile comprised stratigraphic ples. Pollen analysis was carried out on all samples taken at The Landing, situated at samples except 2, 7, and 13. the base of a slope, ca. 3.5 m above sea level Pollen (and spores) was recovered using and <10 m from the water. This sequence the standard acetylation and hydrofluoric records upland landscape change. Further de- acid method (Moore et al. 1991). The sum tails of Pitcairn Island archaeology are dis- comprised 200 pollen and spores, and slides cussed by Gathercole (1964) and Weisler were scanned for types not found in the (1995). count. Relative concentrations of fragments The Henderson Island samples comprise of microscopic charcoal, recovered along samples 9–13. Samples 9 (layer I) and 10 with pollen, were noted subjectively. (layer II) are from a suspected prehistoric Starch residues were recovered by density gardening area (site HEN-20 [Weisler separation using the method given in the 1997]) on the north end of the plateau, just work of Horrocks (2004b). Presence or ab- inland from site HEN-3. Samples 11–13 are sence of starch residues was noted. Identifica- from a suspected prehistoric gardening area tion of starch residues was carried out with (site HEN-23) near the northwestern edge the aid of a modern reference collection, of the plateau between rock shelter sites which includes the starch staples (see begin- HEN-11 and 12 in the cliff face below (Weis- ning of article), minor starch crops, and ler 1997) (Figure 1B). Layer I is recent hu- many of the remaining plants known to have mus, II a suspected gardening layer, and III been cultivated in the prehistoric Pacific. The is sterile subsoil. many studies available on starch grain mor- The Pitcairn Island samples comprise sam- phology were also consulted (Reichert 1913, ples 14–24. Samples 14–17 (layers I–IIIB) are Seidemann 1966, Hoover 2001). from Down Fence, just inland from the The radiocarbon age determinations were northeastern coast of Pitcairn Island in a carried out by Beta Analytic Inc. using stan- small gulch that drains from the plateau at dard procedures for conventional sample Flatlands (Weisler 1997) (Figure 2). Layer I analysis (Weisler 1995). is an historic A horizon and II is possibly his- torically deposited upland clay. IIIA and IIIB are very late prehistoric or very early historic results layers with dispersed macroscopic charcoal. Palynology Samples 18–24 (layers I–VII) are from The Landing, located on the west side of Bounty All except one of the samples analyzed for Bay (Figure 3). Layer I is the A horizon, pollen has high concentrations of micro- Figure 2. Sample from the East profile at Down Fence, Pitcairn Island. Sample numbers and positions are shown in boxes (see Appendix for descriptions). The late radiocarbon age determination for layer IIIB suggests rapid accumula- tion of overburden. Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 267

Figure 3. Sample from The Landing, Pitcairn Island. Sample numbers and positions are shown in boxes (see Appen- dix for descriptions). Much of the profile material is colluvium from upslope. scopic charcoal. The exception, the lower- All of the Pitcairn Island samples con- most sample of The Landing profile from tained sufficient pollen for analysis (Figure Pitcairn (sample 24, Figure 3), has a relatively 4). Like the Marshall Island samples, mono- very low charcoal concentration. Preservation lete fern spores (55–80%) dominated the of pollen ranged from moderately good to palynomorph assemblages in the shorter Pit- poor. None of the samples from the Marshall cairn profile (Down Fence), although Myrta- Islands had sufficient palynomorphs for ceae shrub (up to 25%) and Pandanus tree counting, although a few types were noted (10–15%) pollen and trilete fern spores (up during scanning (Figure 4). Samples 9, 10, to 15%) also had substantial values. In the and 12 from Henderson Island contain abun- longer Pitcairn profile (The Landing), as- dant pollen, the assemblages of which are semblages were dominated by both monolete overwhelmingly dominated by monolete fern fern spores (30–60%) and Pandanus (20– spores (both 95% psilate and 5% patterned). 55%) pollen. Small amounts of Asteraceae The monolete spores in sample 12 were too shrub pollen (long spine) were noted in the degraded to differentiate. Traces of a few uppermost two samples. Pollen of several other types palynomorphs were found in the disturbance-related herbaceous taxa, notably Henderson samples, notably pollen consistent Chenopodiaceae, Poaceae (grasses), and Ci- with Alocasia/Amorphophallus in sample 9 chorieae (a tribe of Asteraceae with distinc- (Figure 5) and pollen of Pandanus in samples tive pollen), occurs in the upper part of the 9 and 10. Because the former is first reported profile. Cyperaceae (sedges) pollen was noted here, modern examples are shown in Figure in the lowermost sample (sample 24 [Figure 6. Pollen of woody trees was not found in 3]). In addition, pollen slides of this sample any of the Henderson samples. show a high concentration of other plant Figure 4. Pollen and starch residue diagram from the Marshall Islands and the Pitcairn Group (see Appendix for sample descriptions). Bars represent pollen percen- tages in samples with sufficient pollen for counting, þ represents pollen noted after count or starch residues noted during scanning of slides, dotted line separates the shorter Down Fence profile from that of The Landing. Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 269 material, which although degraded appears to rocks (2004a), and Horrocks et al. (2004b)]. comprise mainly sclerenchyma cells (not This is based on starch grain and xylem vessel found in any of the other pollen samples in morphology, and raphide concentration. this study). Pollen of woody trees was not (Starch grains are highly concentrated in the found in any of the Pitcairn samples. tubers, whereas calcium oxylate crystals and xylem are found throughout the plant, with raphides in particular often in very high con- Starch Residue Analysis centrations.) Although xylem with helical wall In 13 of the samples examined for starch res- thickening may be found in other taxa, this idues we identified a range of starch residue was virtually the only type of xylem found types (Figure 4). Two of the samples not in the samples. However, xylem vessels (and yielding starch residues, samples 2 (outside druses) of the four cultivated Pacific Araceae pit, Marshalls) and 13 (sterile subsoil, Hen- are difficult to distinguish between species. derson [Figure 1B]), were virtually devoid of The following rationale for Araceae mi- any organic material. In the Marshalls and crofossil identification is from the work of Henderson samples, starch residues comprise Horrocks and Bedford (2005). Of the four spherical to subspherical starch grains, cal- Araceae, Colocasia esculenta can be differenti- cium oxylate crystals (raphides and druses), ated from the other three on the basis of size and xylem vessels with helical walls (Figures of starch grains (Loy et al. 1992). The former 5 and 7). Residues in the Pitcairn samples has a mean grain size of <5 mm (most grains are different, comprising ovate to subtriangu- are <3 mm) whereas Alocasia macrorrhiza, lar, often bell-shaped starch grains, with a , and Amorphophallus paeo- vacuole at the central hilum, fissured in larger niifolius have mean grain sizes of 10–14 mm. grains, and xylem vessels with slitlike pits However, overlap in standard deviations (Figure 8). Calcium oxylate crystals were not within this ‘‘non-Colocasia’’ group, together found with the starch grains and xylem in the with degradation and possible swelling of fos- Pitcairn samples. sil grains due to gelatinization, makes differ- Preservation of the starch residues ranged entiation to species on this basis in our case from good to poor. The starch grains were unreliable. present individually or attached to cellulose The four Pacific Araceae each have several tissue and many showed signs of gelatiniza- types of raphide. However, the types pro- tion: discoloration, swelling, and loss of bire- duced in the most abundance, ‘‘whisker ra- fringence. The color change is from colorless phides’’ (Loy et al. 1992), are difficult to to shades of amber or brown (Horrocks et al. distinguish between species. Fragmentation 2004a). Most xylem vessels were also dis- and degradation exacerbate the problem of colored. Xylem was present as bundles of ves- raphide differentiation. Types distinctive to sels or fragments of vessel elements. Raphides species are produced in relatively far lower were present mostly embedded in cellulose amounts, and none of these was identified tissue and occasionally in bundles and as indi- with certainty in either the Marshall Islands vidual fragments. or Henderson Island samples. Thus, on the The starch residues in the Marshall Is- basis of morphology of microfossils found lands–Henderson Island samples have a com- in the samples, we cannot confidently distin- bination of attributes that occur in the guish between the four Araceae species. Araceae, a family of mainly herbaceous plants However, notwithstanding swelling of grains, with aerial or underground stems or rhi- Colocasia esculenta can almost certainly be zomes, often swollen as an adaptation for ruled out for the starch grains shown in Fig- starch storage (e.g., , rhizomes [all com- ures 5 and 7, typical of those found in the monly referred to as tubers]). [Photomicro- samples, on the basis of size. Although some graphs and descriptions of microparts of of the very large, discoloured grains we clas- modern reference samples of Araceae are sify as swollen (Figure 7D) are within the size given in the works of Loy et al. (1992), Hor- range of several Dioscorea species (mean grain

Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 271

Figure 6. Pollen grains (acetylized) of A, Alocasia macrorrhiza and B, Amorphophallus paeoniifolius from modern refer- ence samples. Acetylized pollen grains of these two species of Araceae are difficult to differentiate from each other but usually can be differentiated from those of the remaining two Pacific aroids: Colocasia esculenta and Cyrtosperma merku- sii. Both of the former are inaperaturate, spherical to subspherical, 32–42 mm in diameter, exine <2.5 mm thick, and psilate. Because Araceae pollen in general does not resist acetolysis (Thanikaimo 1969), acetylized grains can appear different than untreated grains. Although acetylized and untreated grains of C. esculenta are echinate and those of C. merkusii monosulcate, unacetylized grains of A. macrorrhiza are echinate; the spines are destroyed by acetolysis. size of >30 mm), we can also rule these out Pacific. The latter includes Ipomoea batatas, because we did not find any grains with the introduced in prehistoric times and cultivated characteristic eccentric Maltese cross of this for its tuberous roots. genus. The starch residues in the Pitcairn samples discussion have a combination of attributes that occur in Ipomoea, a genus of twining prostrate or The microfossil data from the Marshall Is- scrambling herbs, often lianoid. Starch resi- lands and Henderson Island provide direct dues of different species of Ipomoea are diffi- evidence of introduced Araceae crops. The cult to differentiate. [Photomicrographs and Araceae have a long history throughout the descriptions of microparts of modern refer- tropics and subtropics as a subsistence starch ence samples of Ipomoea are given in the food, with many species cultivated. The four works of Loy et al. (1992), Horrocks introduced Pacific Araceae (Colocasia esculenta, (2004a), and Horrocks et al. (2004a)]. Al- Alocasia macrorrhiza, Cyrtosperma merkusii, though other taxa have xylem vessels similar and Amorphophallus paeoniifolius) originated in to those of Ipomoea (slitlike pits), this was the the Indo-Malayan region (Croat 1979, Hay only type of xylem vessel found in the sam- 1990). The natural distribution of terrestrial ples. Several species of indigenous and intro- Araceae in extends east as far as duced Ipomoea are found throughout the Vanuatu, and one widespread Rhaphidophora g————————————————————————————————————————————————— Figure 5. Prehistoric microfossils consistent with introduced Araceae from Henderson Island (B, C mounted in Caedex, a resinous mounting agent; remainder mounted in glycerol jelly, an aqueous agent). A, Pollen grain (acetyl- ized) of Alocasia macrorrhiza or Amorphophallus paeoniifolius from sample 9 (cf. Figure 6). B, Spherical to subspherical starch grains from sample 10. C, Spherical to subspherical starch grains from sample 10 (those in B) viewed under cross-polarized light, showing Maltese crosses due to birefringence (a feature of all starch grains). The elongated objects are fragments of other plant material. D, Gelatinized spherical to subspherical starch grains in cellulose tissue from sample 9. E, Druse (starlike) from sample 9. F, Bundle of raphides (hundreds) from sample 11. G, Large bundle of degraded xylem vessels from sample 10. H, Bundle of degraded xylem vessels from sample 9, showing helical wall thickening. Scale bars, 20 mm.

Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 273 climber extends to (A. Hay, pers. ing both field and tree cropping, with seven comm.). All other Pacific islands have intro- different cultigens, five of which are unequiv- duced Araceae. ocally introduced, including at least two spe- The starch-residue evidence from the cies of the Araceae. Horticultural diversity Marshalls and Henderson indicates that the would almost certainly have been advanta- Araceae crops were non-Colocasia (i.e., Aloca- geous in such a marginal, barren habitat. sia macrorrhiza, Cyrtosperma merkusii, or The identification of Araceae microfossils Amorphophallus paeoniifolius) and for Hender- in the ancient small pit (sample 1) from the son the pollen evidence allows this to be Marshall Islands was unsuspected because further narrowed down to Alocasia or Amor- similar pits are routinely used today for pre- phophallus. Associated radiocarbon dates sug- serving Artocarpus paste. (Araceae tubers can gest first settlement of Henderson Island probably be stored in subterranean pits for ca. 1,200 yr B.P., at the earliest (Weisler short periods of time, but the identification 1999). As reported by Thompson (1982), the of Araceae macrofossils inside but not outside modern distribution of Alocasia and Amorpho- the pit provides strong evidence for the pres- phallus places their farthest east occurrence ence of the latter.) Although Cyrtosperma is in the Marquesas Islands. We know from the the dominant aroid cultivated in the Mar- previous identification of macrofossil leaf shalls today, we cannot rule out the possibility material (ca. 500 yr B.P.) from a rock shelter that other non-Colocasia species of the Ara- that Cyrtosperma was also present on Hender- ceae were present in the pit; the microfossil son (Hather and Weisler 2000). As suggested evidence in our case cannot differentiate be- by Hather and Weisler (2000), the presence tween the three members of this group, of fossil Araceae on Henderson suggests Cyrtosperma, Alocasia, and Amorphophallus. agrarian practices in the Pacific that may The combined micro- and macrobotanical now be only locally isolated but may have evidence from Henderson indicates local cul- been of considerable importance in the past. tivation of both Alocasia and Cyrtosperma or at Cordyline fruticosa was also introduced by early least transport of leaves (for wrapping par- Polynesians for cultivation; relic plants are cels) and tubers. The lack of starch residues found on the island today, rare on the plateau of other carbohydrate crops such as Dioscorea ridge (Florence et al. 1995, Waldren et al. and Ipomoea in the Marshall Islands samples 1999). With the addition of Aleurites moluc- suggests that Araceae was the common culti- cana, reported growing on Henderson in gen. Pollen of another cultivated member of 1912 and 1922 (Paulay and Spencer 1989) the Araceae, Colocasia esculenta, has been re- and recovered from prehistoric habitation ported elsewhere in the Marshall Islands, sites dated to as early as 700 yr B.P. (Weisler west of Maloelap on Kwajalein Atoll (ca. 1997), Musa sp. dated to 600 yr B.P. (Weisler 1,900–1,600 yr B.P. [Beardsley 1994]). Vir- 1997), Cocos nucifera (coconut) dated to 1,000 tual absence of organic material from the yr B.P. (Weisler 1997), and Pandanus tectorius sample from the sterile subsoil on Henderson (see later in this section), there is combined (sample 13, Figure 1B), which is overlaid by evidence of a horticultural system compris- layers of high organic matter content, sug- g————————————————————————————————————————————————— Figure 7. Prehistoric microfossils consistent with introduced Araceae from the Marshall Islands (mounted in glycerol jelly). A, Clockwise from lower left: gelatinized spherical starch grains in cellulose tissue, fragment of degraded xylem vessel element showing helical wall thickening, and druse from sample 3. B, Fragment of degraded xylem vessel element (left) showing helical wall thickening and druse from sample 3 (those in A), highly visible under cross- polarized light. The starch grains are not visible, having lost their birefringence due to gelatinization. C, Spherical to subspherical starch grains in cellulose tissue from sample 6. D, Clump of gelatinized starch grains from sample 3 show- ing extreme swelling. E, Druse from sample 3. F, Raphides (needlelike) in cellulose tissue from sample 1. The thick elongated object is a fungal hypha. G, Raphides (needlelike) in cellulose tissue from sample 1 (those in F) highly visible under cross-polarized light. Note also small starch grains showing Maltese crosses (arrows). H, Degraded fragment of xylem vessel element from sample 7. Scale bars, 20 mm. 274 PACIFIC SCIENCE . April 2006

Figure 8. Microfossils consistent with Ipomoea from Pitcairn Island (mounted in glycerol jelly). A, Ovate to subtrian- gular starch grain from sample 15, showing central vacuole, fissure at the central hilum, and flattened pressure facets. B, Ovate to subtriangular starch grain from sample 15 (that in A) viewed under cross-polarized light, showing Maltese cross. C, Degraded fragment of xylem vessel element from sample 15, showing alternate slitlike pits. Scale bars, 20 mm. gests that downward movement of microfos- Bounty Bay (on Henderson it is moderately sils in these soils by percolating rainwater has common in coastal Argusia scrub). However, been minimal. given that I. macrantha does not have tuber- Unlike the Araceae microfossils on the ous roots, is not reported as being cultivated Marshalls and Henderson, the Ipomoea micro- by early Polynesians, is found in only the fossils in the Down Fence profile from Pit- two upper layers of a five-layer profile, and cairn are equivocal regarding Polynesian would possibly have found the elevation of cultivation of introduced Ipomoea batatas be- the site unsuitable (Down Fence is >100 m cause of indigenous species of this genus. above sea level), the presence of Ipomoea Cummings (1998) reported possible Ipomoea starch residues in heavily disturbed anthropo- starch granules at a site on Easter Island genic soils points to the cultivation of I. bata- thought to be agricultural. Ipomoea macrantha, tas. A single radiocarbon age determination which occurs throughout the Pacific near sea suggests that anthropogenic landscape distur- level or at low elevations on beaches, arid bance was well under way by late prehistory shores, lagoon cliffs, and in thickets (Smith (i.e., 300 yr B.P. [Weisler 1995]). However, 1991), is indigenous to Pitcairn (and Hender- we do not know if the Ipomoea starch horizons son) Island (Florence et al. 1995). Its current extend into prehistory. The upper of the two distribution is rare at one coastal station at layers in which the starch was found (layer I, Plant Microfossils from the Marshall Islands and Pitcairn Group . Horrocks and Weisler 275 sample 14; Figures 2 and 4) also contains his- stokesii, one of two shrub species of this fam- toric artifacts but the lower layer (layer II, ily on the island, now common in open com- sample 15) does not and therefore may be munities (although see later in this section prehistoric. Microfossil starch of I. batatas regarding Polynesian introductions to Pit- has been identified at a number of prehistoric cairn). Pollen of the other species, the en- Polynesian sites in New Zealand (Horrocks demic Bidens hendersonensis var. hendersonensis, 2004a), as have macrofossils (e.g., Yen and has longer spines (Florence et al. 1995), al- Head 1993). Other direct, unequivocal pre- lowing the two to be differentiated. historic evidence of this crop in Polynesia is As with Henderson Island, the pollen as- the pollen from the Society Islands (ca. 1,150 semblages from Pitcairn (Figure 4) also sug- yr B.P. [Parkes 1997]) and Easter Island gest a disturbed landscape with extensive (ca. 700–300 yr B.P. [Cummings 1998]) and fernland, deforested by fire. The late radio- the macroremains from the Cook Islands carbon age determination for layer IIIB, (ca. 1,000 yr B.P. [Hather and Kirch 1991]) Down Fence, at 140 G 70 yr B.P., from and Hawai‘i (ca. 500 yr B.P. [Rosendahl and @2.25 m below surface (Figure 2), suggests a Yen 1971]). Lack of starch residues in The rapid accumulation of the overburden, and Landing profile from Pitcairn suggest that if the colluvial nature of The Landing profile that area was gardened, starch crops did not (Figure 3) also indicates large-scale erosion, feature. consistent with human modification of the The lack of pollen in the samples from the uplands. Pitcairn Island has 16 or 17 indige- Marshall Islands is presumably a result of nous and two endemic species of ferns, in- poor pollen preservation. Compared with silt cluding epiphytic, epilithic, and terrestrial or clay soils, coarser-textured soils such as forms (Florence et al. 1995). As well as plen- coral sands and gravels are typically pollen- tiful ferns, abundant Pandanus trees were also poor. The three Henderson Island samples present near the two Pitcairn sites, especially that contained sufficient pollen for counting The Landing, and as on Henderson, perhaps were from coralline sediments and had rela- cultivated. There are currently no radiocar- tively high levels of organic matter. bon age determinations for The Landing The extremely high values of fern spores profile. However, assuming that Pitcairn was coincident with microscopic charcoal and the abandoned at a similar time as Henderson apparent absence of pollen of woody trees in (ca. 500 yr B.P.), prehistoric artifacts (basalt the Henderson Island samples (Figure 4) sug- flakes) in layer V (sample 22 [Figure 3]) are gest at least a partially deforested, disturbed at least several centuries old. Today Pandanus landscape, at least near the sampled sites, tectorius is found on Pitcairn along the strand with extensive areas of fernland. Henderson line at West Harbour (Waldren et al. 1995). has nine indigenous species of ferns, compris- Along with ferns and Pandanus, the vegetation ing epiphytic, epilithic, and terrestrial forms in the vicinity of the Down Fence site also (Florence et al. 1995). Some Pandanus trees would have comprised Myrtaceae shrubs and would have grown or perhaps been cultivated Cyathea tree ferns. There are two indigenous in the vicinity of the site of samples 9 and 10, Myrtaceae species on Pitcairn: Metrosideros which, along with at least two species of Ara- collina and Eugenia reinwardtiana (Florence ceae, may have been part of a mixed cropping et al. 1995). The often poor preservation of system. Two forms of P. tectorius (possibly in- the Mytaceae pollen in the samples did not volving Polynesian cultivars) occur on the is- allow confident differentiation between these land and are very common throughout, often two taxa. Today the former occurs occasion- forming small groves (Florence et al. 1995). ally on dry crests and slopes in open com- As with other taxa known to be used by Poly- munities; the latter is rare on coastal cliffs at nesians, it is not clear whether it is indige- Bounty Bay. Syzygium malaccensis (Malay ap- nous, introduced, or (perhaps most likely) ple), a cultivated tree introduced by humans both. The Asteraceae pollen in sample 9 throughout the Pacific, should also be con- would have come from the indigenous Senecio sidered as a possible source of the fossil 276 PACIFIC SCIENCE . April 2006

Myrtaceae pollen. The indigenous Cyathea long before the earliest recorded Polynesian medullaris is the only tree fern in the Pitcairn settlement (Macphail et al. 2001). At this Group flora (Florence et al. 1995). Today it is stage we cannot determine this for Pitcairn, rare below the summital crest in a disturbed because neither of our pollen profiles appears Metrosideros/Homalium forest and very rare to include prehuman times. elsewhere on Pitcairn. The relatively low concentration of char- conclusions coal and high concentration of plant material (sclerenchyma cells) in the lowermost sample The identification in this study of microfos- of The Landing profile from Pitcairn (sample sils of cultigens (at least for the Marshalls 24 [Figure 3]) suggests initial human impact and Henderson) in soils of all three Pacific is- on the island. The plant material in that layer land types (atolls, raised atolls, and volcanic may be from vegetation growing on the soil islands) and in two far-distant archipelagos in at the time, which was subsequently buried Micronesia and Polynesia shows the potential by upslope erosion. The presence of pollen for this type of analysis in Oceania and else- of the disturbance indicators Chenopodia- where. Araceae evidence is unequivocal be- ceae, Poaceae, and Cichorieae in the upper cause of absence of indigenous members of part of the profile (Figure 4) suggests vegeta- this family from most of the Pacific. How- tion succession, a result of progressive in- ever, at this stage it is difficult to differentiate crease in the frequency or intensity of the the non-Colocasia Pacific Araceae preserved in disturbance regime. Cichorieae in particular the types of deposits analyzed in this study. is a universally common pollen indicator of The problem of differentiating individual human disturbance of vegetation. Only one species within the same group also applies to indigenous species of Poaceae is recorded for Ipomoea, indigenous species of which are Pitcairn: Lepturus repens, today rare in coastal widespread in the Pacific. A possible solution vegetation at Bounty Bay (Florence et al. would be analysis of plant DNA preserved in 1995). soils. Extremely low pollen concentrations in The Chenopodiaceae, Cichorieae, Cypera- some coral sediment samples, in our case ceae, and Pteris pollen evidence from Pitcairn from the Marshalls, could probably be over- is interesting because indigenous species of come by analyzing larger-volume samples these taxa were not recorded in a recent veg- (e.g., by using a 10- to 15-cm3 sample instead etation survey of the island (Florence et al. of the standard 1- to 3-cm3 volume). The 1995), suggesting Polynesian introduction, identification of starch residues of cultigens probably accidental. Atriplex and Chenopodium in these pollen-poor samples shows the value species are likely candidates for Chenopodia- of combining the different types of micro- ceae; Cyperus, Mariscus, and Fimbristylis for fossil analysis. Cyperaceae; Woolastonia biflora for Cichor- The geographically marginal and environ- ieae; and P. tripartita and perhaps P. vittate mentally depauperate islands of the eastern for Pteris (Smith 1991; J. Braggins, pers. Pacific challenged human colonists to their comm.). Another possibility is that taxa of limits. Although previously uninhabited is- these pollen types were native to Pitcairn, be- lands, with their pristine stocks of fish, shell- coming extinct during Polynesian occupation. fish, turtles, and seabirds, would have This could be the case for Cyperaceae, pollen attracted colonists, sustained occupation re- of which was found only in the earliest, low- quired some level of horticulture or regular ermost sample. However, Chenopodiaceae, contact with larger, more diverse islands for Cichorieae, and Pteris are typically distur- needed resources (Weisler 1997, 2002b). bance related and therefore would presum- The documentation of a mixed cropping re- ably not be adversely affected by human gime on Henderson Island in Southeast Poly- activity. A pollen study from Norfolk Island nesia implies a more permanent and sustained in the Southwest Pacific showed that some presence on the island. 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7: Ebon Islet, Ebon Atoll, layer IV. A very pale brown 15: Layer II, Down Fence. A yellowish red (5YR4/6) silty (10YR7/3) medium to coarse sand. clay with dark red (2.5YR4/8) saprolites, few cobbles, 8: Enilok Islet, Ebon Atoll, within large pit. A black and minor amounts of dispersed charcoal. (2.5YN2/0) sandy sediment. A radiocarbon age deter- 16: Layer IIIA, Down Fence. A reddish brown (5YR4/3) mination of 1,560 G 70 yr B.P. (Beta-92134 [Weisler gravelly silt with dispersed charcoal and abundant 2002a]) caps the sample. cobbles. 17: Layer IIIB, Down Fence. A dark reddish brown Henderson Island (5YR3/3) gravelly silt with minor dispersed charcoal 9: Layer I, suspected gardening area. A very dark brown and abundant cobbles. (10YR2/2) humus-rich, silty A horizon with very little 18: Layer I, The Landing. A brown (10YR4/3) silty clay sand and dense roots. A horizon with no charcoal. 10: Layer II, suspected gardening area. A dark yellowish 19: Layer II, The Landing. A yellowish red (5YR4/6) silty brown (10YR3/4) gravelly silt with rare charcoal clay with cobbles and no charcoal. flecks. 20: Layer III, The Landing. A brown (10YR4/3) silty clay 11: Humus (layer I). An A horizon consisting of a black with dispersed charcoal and few cobbles. (5YR2.5/1) humus-rich sand and decomposed coral 21: Layer IV, The Landing. A reddish brown (5YR4/4) gravel layer. silty clay with dispersed charcoal and cobbles. 12: Suspected gardening layer (layer II). A brown 22: Layer V, The Landing. A brown (10YR4/3) silty clay (10YR4/3) sandy gravel with dispersed charcoal. prehistoric cultural layer with dispersed charcoal, ba- 13: Sterile subsoil (layer III). A yellowish brown (10YR5/ salt flakes, and combustion features. 8) coarse-sand sterile subsoil with very little coral. 23: Layer VI, The Landing. A yellowish red (5YR4/6) silty clay with rare dispersed charcoal and cobbles. Pitcairn Island 24: Layer VII, The Landing. A reddish brown (5YR4/4) 14: Layer I, Down Fence. A dark brown (10YR3/3) silty clay. A horizon with historic artifacts.