ATOLL RESEARCH BULLETIN No. I60
REEF ISLANDS OF RAROTONGA
by D . R . S t o d d a r t
LIST OF VASCULAR FLORA
by F . R . Fosberg
I s s u e d by
THE
SMITHSONIAN INSrnrnION Washington, D. C., U. S. A.
ileccrnber 31,
19'(2
F i g m e
1 . Bathymetry of the Southern Cook Islands. Based o n Summerhayes (1967)REEF ISLANDS 01.' RAROTONGA
by D.R. Stoddart
INTRODUCTIOX
Remarkably little i s know!^ of the c o r a l r e e f s of Rarotonga, southern Cook Islands. C r o s s - land (1928a. 616-619) and Davis (1928, 407-408) gave brief descriptions following s h o r t v i s i t s , and r e m a r k s on reef s t r u c t u r e in the context of the geological history of the island have been made by M a r s h a l l (1908, 1912, 1930) a n d l a t e r w o r k e r s (Wood, 1967).
A marine biology p a r t y f r o m the Cook Bicentenary Expedition to the Southwest P a c i f i c worked on Rarotonga f r o m 21 to 27 August 1969. The party consisted of Dr. H.G. V e v e r s (Zoological Society of London), Dr. P.E. Gibbs (The Marine Laboratory, Plym,suth), and the author. A f t e r a reconnaissance of the coast of Rarotonga, work was concentrated a t Ngatangiia Harbour on the e a s t s i d e of the island, though s o m e collections were a l s o made at other locali- ties. Subsequently the Ngatangiia a r e a was a l s o visited by Prof. W.R. P h i l i l ~ s o n (Department of Botany, University of Canterbury, Christchurch, New Zealand), during floristic studies c a r r i e d out on the s a m e expedition, and s o m e of h i s r e s u l t s a r e used here.
The p r e s e n t paper gives a general description of the r e e f s and environmellt of Rarotonga, a detailed account of the reef islands of Ngatangiia, a n d a l i s t of the vascular f l o r a of the islands determined by Dr. F.R. Fosberg (Smithsonian Institution). Other r e s u l t s of the Ngatangiia work will appear elsewhere. A preliminary account of c o r a l reef studies in the Cook Islands during the 1969 expedition h a s a l r e a d y been published (Gibbs, Stoddart and V e v e r s , 1971).
R E E F GEOMORPHOLOGY
Rarotonga (latitude 21012'S, longitude 1 5 9 0 4 6 ' ~ ) i s a n i s o l a t e d volcanic island, now dee1)Iy dissected by erosion, with a maximilm altitude of about 640m. It r i s e s f r o m the ocean floor a t a depth of about 4000m (Summerhayes and Kibblewhite, 1967), a t which depth the volcanic cone is 45-55 k m in diameter (Figure 1). The p r e s e n t island has m a x i m u n ~ dimensions of 11.5 x 8km. The exposed volcanics consist of basaltic and phonolitic eruptives; the l a t t e r have been dated radiometrically a t 2.3-2.8 million y e a r s , indicating a Pliocene age f o r the upper- m o s t lavas of the cone (Tarling, 1967). The volcanics a r e surrounded a t the coast by a low apron of g r a v e l s and sands (Fig. 2). The gravels (Nikao Gravels) were deposited f i r s t and sligl~tly cliffed b e f o r e the deposition of the m o r e r e c e n t Aroa Sands (Wood, 1967). Swamp deposits in p l a c e s occupy g a p s between the g r a v e l s and the beach ridges of the Aroa Sands, particularly along the south and west coasts. Small a r e a s of elevated reef limestone outcrop in places round the coast, a n d m?y be extensive beneath the Aroa Sands; t h e i r significance will be discussed l a t e r .
(Manuscript
received
O c t . 1971--Eds . )T h e island is surrounded by a fringing reef about 400 n1 wide along the south and 200 In wide along the west and north coasts. In Ngatangiia Harbour the reef e d p l i e s about I k m f r o m the coast. The reef edge is conthiuous except f o r steep-sided n a r r o w inlets a t Avatiu and Avaroa on the north coast, Ngatangiia on the e a s t , and s e v e r a l p l a c e s on the south. The r e e f f l a t s a r e planed-rock f e a t u r e s , r a r e l y c a r r y i n g m ? r e than 1.5ni ?f water even a t high tide; they a r e covered with sand sheets, and growing c o r a l s a r e not common. Marine phaneroganis a r e absent; These flats a r e distinguished, especially at Ngatangiia Harbour, by e x t r e m e l y l a r g e p ~ p u l a t i o ~ ~ s of holothuriaus, with densities of Ifololizuvia al7,a reaching up to 1 0 p e r s q m. Ail a l g a l ridge is only weakly developed o n t h e r e e f s , though Marshall (1930) s t a t e s that i t is higher in the south than the north.
C r o s s l a n d (1928a, 616-619) considered that the r e e f w a s o r i g i n a l l y a b a r r i e r r e e f converted to a fringing reef by infilling of the lagoon by the c o a s t a l s a n d s and gravels. He s a i d little of the composition of the reef, except to note the existence of l a r g e b r a i n c o r a l s and a l s o of I'ovites heads in the boulder beach a t Avarua (Crossland, 1928b, 721). Davis (1928, 407-408) r a t h e r misleadingly r e f e r r e d to Rarotonga's "close-set and little-eroded b a r r i e r reef, from a q u a r t e r to a half m i l e wide, now about 15 f e e t above s e a level, enclosing a n a r r o w lagoon flat o r swamp"; he considered that the amount of sediment produced during dissection of the island, both before and during r e e f growth, r e q u i r e d considerable subsidence for i t s disposal, and that t h i s o v e r a l l sinking of the island was to be distinguished f r o m the m o r e r e c e n t 5 n~ uplift of what he t e r m e d the b a r r i e r reef, and the subsequent infilling of i t s lagoon.
Ngatangiia Harbour on the west coast form:; the m o s t pronounced c o a s t a l indentation.
Rarontonga's l a r g e s t r i v e r , the Avana, flows into the harbour and d i s c h a r g e s by the deep r e e f g a p north of Motutapu (Fig. 3). Outcrops of elevated reef limestone a r e found on both s i d e s of the harbour entrance. The Harbour islands, f r o m Motutapu southwwds, continue the general t r e n d of the coast (though Taakoka is volcanic, not detrital). Wood (1967) m a p s the detrital i s l a n d s as A r o a Sands, and both M a r s h a l l (1930) and Wood (1967) draw attention to the absence of s a n d s a n d g r a v e l s on the mainland c o a s t of Ngatangiia Karbour, where volcanic r o c k s r e a c h the sea. Marshall (1930, 19-20) proposed that the d e t r i t a l islands r e p r e s e n t e d f r a g m e n t s of a formt?rly continuous beach ridge breached by h u r r i c a n e s , with a s a r e s u l t the s e a flooding the
swampy f o r m e r back-ridge a r e a .
Harotoi~ga l i e s in the South-east T r a d e Wind belt. T h e r e a r e no c l i m a t i c data for the Ngatangiia a r e a , on the windward, wetter s i d e of the island. Avarua, on the leeward side, has a mean annual rainfall of about 2050mn1, though with considerable variation between years.
Most of the r a i n f a l l s d u r i n g M a r c h , A p r i l a u d May; and the d r i e s t months, with l e s s than 1 0 0 m m average, a r e July and September. Mean aimual t e m p e r a t u r e i s 23.6OC. Highest recorded t e m p e r a t u r e n e a r s e a level a t Avarua is 33.5OC, ai1dlowest8.9~C (Marsha111930; Grange and Fox 1955).
T h e island is frequently affected by s t o r m s of h u r r i c a n e intensity, generally approaching from :he northwest. Major r e c o r d e d s t o r n w a r e those of December 1831, December 1842, M a r c h 1846 (especially damxging a t Ngatangiia), Decem'3er 1848, March 1926, M a r c h 1943, January 1944, January 1946, December 1948, and September 1950 (Gill, 1885; Marshall, 1930;
Hutchings, 19531, but this l i s t is c l e a r l y incon1.Aete. Because of the open-ocean situation, s t o r m s u r g e s associated with h u r r i c a n e s a r e not important; m m t of the effects a r e f r o m wind a n d wave activity. Tsunamis a l s o occasionally o c c u r . Those of May 1960 resulting f r o m the Chileail earthquakes reached the comparatively low height in inlets a t Rarotonga of 1.5 m above norm21 s e a level, partly because the tide waslow a t the time and normal water level was below the outer r e e f edge (Keys, 1963). Both h u r r i c a n e s a n d tsunamis, however, a r e likely to have been significant controls in the development of the r e e f islands.
T i d e s a r e sem!.-diurnal, with a r a t h e r pronounceddiurnalinequality a t and following neaps.
According topredictioilspreparedby the HydrographicDepartment,Ministry of Defence, London, for the expedition, in 1969, the range a t s p r i n g s is 0.85 m a n d a t neaps 0.33 m.
DESCRIPTION O F THE ISLANDS
Mstutapu is the n o r t h e m m i s t and 1argestoftheNgatangiia islands: i t is 6 0 0 m long, 360m wide, with a n a r e a of 11 ha. The northern p a r t of the island consists of a rough makatea o r elevated reef limestone, well cemented, with a local relief of up to 1 m though with a r a t h e r subdued erosional topography (Plate 1); i t i s cliffed and undercut a t intertidal levels, and i t s upper surface stands a t 2-3 m above the s e a (Plate 2). A s m a l l patch of s i m i l a r rock outcrops f u r t h e r south on the seaward shore, and much of the northeastern p a r t of the island is presum- a b l y underlain by this limestone. At the north point the nzakatea directly overlooks the deeper w a t e r of the harbour entrance, and s i m i l a r rock outcrops on i t s northern side.
Apart f r o m the nzaizatea the island is a simple cay, with a gravel and cobble ridge and intertidal s t o r m rubble forming a beach up t o 5 m high on i t s seaward s i d e (Plate 31, and a wide intertidal expanse of fine sand and silt forming a n Uca-dominated flat on i t s leeward side. The seaward beaches a r e 25-30m wide; those on the l e e side a r e n a r r o w e r a s well a s lower. All a r e aggrading except for a cliffed s e c t o r of cobble beach on the north coast.
The vegetation of the inaka2ea differs f r o m that of the r e s t of the cay. S e s ~ v f u l l l Polstu- lacastvum c o v e r s the floors of potholes, with a low s c r u b of Wedelia bzflova and Ca/@a9,avis covdifolia. Ifeliotvopiui?i ano?mzlmn and Iponzoea p e s - c a p ~ a e a r e a l s o present. Most of the c h a r a c t e r i s t i c s t r a n d plants of the sand cay a r e absent.
On the seaward coast of the sand cay section t h e r e i s a long n a r r o w zone of Scaevola taccada, with some scattered bushes of Tozivnefovtia avgenlea and a patch of Lantana canzava.
Outpost vegetation is r e s t r i c t e d to s m a l l a r e a s of Vigna nzavina and Cassyliza filifovinis.
The Scaeuola, in places up to 4 m tall, i s replaced inland by a dense woodland of IIihiscus tiliaceus 6-8m tall, with s o m e Guettavda, Mog,inda, Caszcariua, and occasional conspicuous
tall coconuts. The interior of the c a y i s occupied by a higber woodland, dominated by coconuts, with H e w a n d a sono?*a, Leucaena insulamin, Morinda citvifolia, Cavica papaya and other spe- cies. Cn the low-lying, partly waterlogged l e e s h o r e t h e r e a r e a r e a s of g r a s s and sedge m a r s h dominated by a s t e r i l e g r a s s (possibly i'aspalunz) and inhabited by Uca.
Onevoa (Fig. 5)
Oneroa, south of Motutapu, is slightly s m a l l e r ; it l a c k s the nzakalea but is otherwise s i m i l a r i n topography and vegetation. The island is 500 m long and 200-250m wide, with a n a r e a of 10.611a.
The s e a w a r d beach (Plate 4 ) consists of sand, gravel and cobbles, with broken c o r a l rubble a t i t s foot and strewn a c r o s s i t s s u r f a c e ; the c o a r s e r sediments a r e m o r e common in the south- east. The beach is 2 0 m wide and 2-3 m high. The leeward beach is low and sandy, with a sand spit 1 0 0 m long extending lagoonward in the norih. This s p i t encIoses, a s a t Mgtutapu, a wide intertidal flat of sand and fine gravel with l a r g e n u m ' x r s of Uca. Cemented rubble f o r m s a low shelf a t the foot of the s e a w a r d beach towards the north, but otherwise t h e r e is no beach- rock.
The n a i n vegetatio.1 ?P the island is 2 mixed woodland d%ninatecl by Casuarina, broldleaf t r e e s and coconuts. IIiOiscus liliaceus is a n important component, together with ilemandia sonova, I'isonia p a n d i s , 1Vovinda c i i ~ i f o l i a and I.eucaena inszilavum. Several s p e c i e s of f e r n s
f o r m a ground cover. Casuavina reaches the s h o r e in s e v e r a l places, and is locally being undermfned by beach erosion. Scaevola taccada f o r m s a n interrupted beach-crest s c r u b up to 4 m tall, with s o m e Touvnefovlia and Guettavda, on the seaward shore. Inland f r o m the narrow Scaevola belt is a zone of taller Pisonia and Hevnandia woodland40-50 m wide, largely growing on c o a r s e beach-crest c o r a l rubble with no other ground cover. At the abrupt inner edge of the rubble spread, on s a n d and fine gravel, the vegetation changes t o a mixed woodland dominated by Casuavina with a ground cover of f e r n s a n d g r a s s e s . The Scaevola belt is wider and m o r e continuous on the lagoon shore, again with occasional Toumefovtia: Sopl&o?,a and Suviana a r e r e p r e s e n t e d by isolated bushes. Outpost s p e c i e s o n the beach outside the Scaevola
zone include Cassytlza, Cencinus and Tviumfetta.
Kovonzivi (Fig. 6 )
Koromiri, the s m a l l e s t of the c a y s (320 mlong, 1 2 0 m wide, a r e a 3 ha) strikingly r e s e m b l e s Oneroa in i t s topography, with a prominent northern sand spit. The beaches a r e narrower, however, and on the southeast coast cliffed and retreating. The island is distinguished by its relict beachrock extending up to 1 2 0 m seaward of the cay.
Apart f r o m patches of He?-nandia, Hibiscus, Mavinda and Guettavda woodland, the islaud is covered with Casuavina woodland. Beach-crest s c r u b of Scaevola taccada, witli some Toumefovtia avjientea, is m o s t continuous on the lag0011 shore, where Cassytlza is abundant.
Outpost vegetation is very limited, wit11 some Vijina mavina and Tviumfetta pvocu?nbens.
Taakoka
Taakoka, the southernmost island, s e t well back f r o m the reef edge, is not a sand cay but a low hill of basalt forming a n island half the s i z e of Koromiri. The island may be described in two p a r t s . F i r s t , a central plateau, consisting of a jumble of large angular and sub-rounded basalt blocks, encrusted with lichens and covered witli bryophytes, and surrounded on i t s sea- ward m a r g i n s by l a r g e spreading t r e e s of Ijavvirgtonia asialica 10-15111 tall. I11 the centre of the plateau there a r e some 50 coconut t r e e s 15-25 m tall, with Mavinda, Hevnandia and f e r n s . The plateau s t a n d s about 6 m above s e a level. Second, there i s a "tail" lagoonward of the plateau, of basalt blocks up to 1 m 'ong. T h i s has a n outer zone of Casuavbza up to 20 m fall, with Vijina nzavina and Iponzoea nzacvantila beneath, and a n inner zone of Hevnandia, 10mtal1, with Movinda, coconuts and f e r n s .
Scaevola grows abundantly a m m g the basalt blocks of the seaward coast, with Wedelia bzflova, Vigna m a h a and Iponzoea pes-capvae. Along the northandsoutllshores Bavvingtonia approaches close to the beach, with thickets of Hibiscus tiliucezls and outpost Vig-no nzavina and Ipomoea wzac?~antl7a.
Several s p e c i e s a r e clearly introduced, though the island is not inhabited. These include not only the coconuts, but cultivated Hibiscus and Ilippeast?-um, and a single banana plant.
It is c l e a r that Taakoka, s o different physiographically, has little in c o m n o n with the other three islands, and i s ,mly linked with themby proximity. Along the north s h o r e there i s a thick outcrop of beachrock, consisting of angular basalt cobbles in a r e d clayey m a t r i x which is presumably a decomposition product of the basalt. The beach sands, a s on the other islands, a r e , however, reef-derived.
D S VELOPMSNT O F T H E ISLANDS
F r o m these s u r v e y s of the cays, i t is not possible t o confirm Marshall's proposal (1930, 19-20) that the islands f o r m p a r t of a f o r m e r l y contin?ious ridge of Aroa Sands fragmented by s t o r m action. T h i s could be so, but equally the islands have a l l the c h a r a c t e r i s t i c s of ordinary cays, and they show no obvious signs of m a j o r e r o s i o n o r dissection. Nor is t b e r e any evidence b e t w e n the islands, e.g. in relict beachrock, of f o r m s r l y m o r e continuous land. The islands, other than Taakoka, consist of successive increments of storm-deposited rubble and cobbles of reef origin on the s e a w a r d beaches, with infill and spit-growth of fine gravel and s a n d to leeward. It s e e m s likely that these p r o c e s s e s of aggradation a r e s t i l l active. The islands in their present form a r e not therefore directly reIated to the occurreuce of r a i s e d r e e f r o c k rcmnants in the nzakalea of Motutapu and the mainland coast. T h e r e a r e a l s o two smrll islands on the northern r e e f f l a t s of Rarotonga: one n e a r Avatiu h a s been much a l t e r e d by land reclamation on the reef flat, but the other, Motu Toa, h a s probably a l s o originated by sedim,?nt accretion to f o r m a discrete island on the reef flat.
Som,? data a r e available on the absolute chrol?clogy of late Pleistocene and Holocene events a t Rarotong-a. Schofield (1970) h a s published
cl*
dates on inakutea s a m p l e s : a s a m p l e f r o m Ngatangiia Harbour, elevation 3.05 m , is datedat 28,200t
850 y r B.P., and one at T e A r a Vaka, elevation 1.83m, a t m o r e than 48,900 yr. A s a m p l e f r o m 3.2m elevation at Matavera could not be dated. Schofield suggests that the reef f r o m which these s a m p l e s were taken (equivalent to the Mstutapu inalzalea) WAS formed during an interstadial a t 32,000-35,000 y r B.P.; i t is per- h a p s m o r e probable, in view of the difficulty of dating such material, that i t c o r r e l a t e s with the iizakateaof Mangaia, f o r which Veeh (1966) obtaiued a u r a n i u m - s e r i e s age of 110,000t
50,000 yr.
T h e r e is son?? evidence f r o m Rarotonga f o r much m o r e recent high s t a u d s of ths sea. A r a i s e d reef a t Avarua on the north coast, a t 1 m above p r e s e n t low water level, with c o r a l s in the position of growth, h a s beendatedat2030 ? 60 y r B.P., and soil sam:>les f r o m beach ridges of Aroa Sands age have h e n dated a t 1235
1
57, 2470i
63, aud 3510i
50 y r B.P. (Wood 1967;Schofield 1970). Schofield a l s o r e p o r t s a beachrock at Titikaveka a t 1 m :?hove p r e s e n t high w a t e r level. He suggests that these recent dates indicate s e a stauds a t t 2 and t l m above the present, and that the Aroa Sands beach ridges, which r i s e to about 8 m above p r e s e n t s e a level, w e r e f o r m e d during these higher stands. T h e r e is no evidence of such stands in the topography of the Ngatangiia reef islands, and indeed l a r g e p a r t s of the islands would be subm;.rged with such higher s e a levels. It should be noted that the much older Motutapu mahalea is tidally notched at p r e s e n t intertidal levels, and t b e r e a r e no apparent signs of higher notches.
The Ngatangiia islauds can thus be assumed, f r o m their own c h a r a c t e r i s t i c s , to have had a s i m p l e aggradational history, punctuated by hurricane events, accumulating on reef f l a t s partially f o r m e d by the erosion of older elevated reef limt?stone. It i s possible that they a r e younger than the sea-level events described by Schofield, o r that the evidence of such events in the physiography of the islands h a s been e r a s e d by l a t e r s t o r m ~ c t i o n .
SUMMARY O F VEGETATION
The vegetation of the islands is relatively simple. Essentially it c o m p r i s e s a broadleaf woodlaud of Hzbiscus, L;uettaisda, llgbvinda, l'isonza am3 Hevnandia, with coconuts and Casuavina, the l a t t e r apparently spreading a t the expense of broadleaf t r e e s ; a beach-crest s c r u b of Scaevola taccada with somt? Toumefovtia avrentea; ai1.J. ;in outpost o r ~ > i o n e e r s t r a u d vegetation, very patchily developed, of T v i u n z f e t ~ , ifiovzoea, i'iX.7~ and o t h e r species. The Motutapu iizakalea h a s i t s owndistinctivevegetationof Wedelia biflova, Ifiolizoea, H e l i o t l ~ ~ f i i ~ ~ z , and Cafil~avis cor~dzfolia. 111-drained leeward s a n d f l a t s have a low .Tegetation of g r a s s e s and sedg.es. T h i s r e s t r i c t e d range of vegetation types r e f l e c t s the lim'ted range of habitats and the
6
s m a l l s i z e of the i!
woodland, a r e found or
;lands, as well as f l o r i s t i c poverty. Somt? types, notably B a ~ ? ~ i @ o n i a ily on Taakoka a n , l not on the s a n d cays.
T h e r e is no mangrove vegetation, and s e a - g r a s s e s a r e absent, not only on Rarotonga but throughout the Cook Islands. Some s p e c i e s , especially l i t t o r a l s h r u b s , a r e s u r p r i s i n g l y r a r e , p a r t i c u l a r l y k v i a n a nzavitima, which i s extremely comlnrm o n Aitutaki on s i m i l a r cays.
Wilder (1931) r e c o r d e d this s p e c i e s a s o c c u r r i n g only on Motutapu; it w a s not s e e n t h e r e i n 1969, but a single specimen was growing on Oneroa.
ACKNOWLEDGEMENTS
I thank the Royal Society of N e w z e a l a n d a n d the Royal Society of London f o r the opportunity t o take p a r t in the Co3k Bicentenary Expedition. O u r work was supported by the Cook Island Government through the P r e m i e r , Hon. Albert Henry. T h e l a t e M r . L. Peyroux a c t e d a s E x - pxlition Liaison Officer with the P r e m i e r ' s O f f i c e . I a m grateful t o the Rev. B e r n a r d Thorogood a n d o t h e r m e m b e r s of the Cook Islands L i b r a r y and Museum Association; t o Mr. Dawson M u r r a y of T e r i o r a College, Rarotonga; t o P r o f . W.R. Philipson f o r m l k i n g s o m e of h i s own r e s u l t s available; to Dr. F.R. F o s b e r g f o r making the plant identifications; and t o Dr. H.G. V e v e r s a n d Dr. P.E. Gibbs f o r a s s i s t a n c e in the field.
REFERENCES
Crossland, C. 1928a. C o r a l r e e f s of Tahiti, Moorea and Rarotonga. J. Linn. Sac. Lond. 36:
577-620.
Crossland, C. 1928b. Notes on the ecology of the r e e f - b u i l d e r s of Tahiti. P r o c . Zool. Sac.
Lond. 1928: 717-735.
Davis, W.M, 1928. T h e c o r a l reef problem.. Amer. Geog. Sac. Spec. Pub. No. 9: 1-596.
Gibbs, P.E., Stoddart, D.R., and V e v e r s , H.G. 1971. C o r a l r e e f s and a s s o c i a t e d cominirnities in the Cook Islands. Bull. Roy. Sac. New Zealand 8: 91-105.
Gill, W.W. 1885. J o t t i n g s f r o m :he Pacific. London: The Religious T r a c t Society. 248pp.
Grange, L.I. and Fox, J.P. 1953. Soils of the Lower Cook Group. New Zealand Soil Bureau Bull. n.s. 8: 1-55.
Hutchings, J.W. 1953. T r o p i c a l cyclones in the southwest Pacific. New Zealand Geographer 9: 37-57.
Keys, J.E. 1963. T h e t s u n a m i of 22 May 1960 in the Samoa and Cook Islands. Bull. Seis.
Sac. Amer. 53: 1211-1227.
Marshall, P. 1908. Geology of Rarotonga and Atiu. T r a n s . New ZealandInst. 41: 98-100.
Marshall, P. 1912. C o r a l r e e f s of the CookandSociety Islands. Rept. 13thMeetingAustralasian Assoc. Adv. Sci. (Sydney 1911): 140-145.
Marshall, P. 1930. Geology of Rarotonga and Atiu. Bull. B e r n i c e P. Bishop Mus. 72: 1-75.
Schofield, J.C. 1970. Notes on l a t e Q u a t e r n a r y s e a levels, Fiji and Rarotonga. New Zealand J. Gsol. Geophysics 13: 199-206.
7 Summerhayes, C.P. 1967. Bathymetry and topographic lineation in the Cook 1sland.s. New
Zealand J. Geol. Geophysics 10: 1382-1399.
Summerhayes, C.P. and Kibblewhite, A.C. 1967. Rarotonga provisional hathymetry. New Zealand Oceanographic Institute Chart, Island Series, 1: 200,000.
Tarling, D.H. 1967. So!ni- paleomngnetic r e s u l t s fro!n Rarotonga, Coak Islands. New Zealand J. Geol. Geophysics, 10: 1400-1406.
Veeh, H.H. 1966. T ~ ~ and ~
u
~~
/~
ua g e s of Pleisiocene high s e a level stand.~
~/
~u
~~ ~ ~
J. Ge:>phys. Res. 71: 3379-3386.
Wilder, G.P. 1931. F l o r a of Rarotonga. Bull. Bernice P. Bishop Mus. 86: 1-113.
Wood, B.L. 1967. Geology of the Cook Islands. New Zealand J. Geol. Geophysics 10: 1429- 1445.
9 LIST O F VASCULAR PLAYX'S
by F.R. F o s b e r g
P l a n t s collected in 1969 and deterlnined by Dr. F.R. F o s b e r g , together with those collected
011 the c a y s by P r o f , W.R. Pnilipson, c o m p r i s e 2 bryophytes (not determined), 1 lichen (nst
&:ermined), a n d 49 s p e c i e s of v a s c u l a r plants, including 4 s p e c i e s of f e r n s . Som,? e a r l i e r r e c o r d s , usually without p r e c i s e lo:ation, a r e given in the f l o r a s of Cheeseman (1903) a n d W i d S l One s p e c i e s r e c o r d e d on Motutapuby Wilder, A";opo?ulln sandinricense A. Gray, w a s not collected in 1969.
Of t h e p l a n t s ill the following l i s t , e x c l u d i n g f e r n s , 26 s p e c i e s a r e r e c o r d e d f r o m Motutapu, 17 f r o m Dneroa, 14 f r o m K o r o m i r i , a n d 18 f r o m Taakoka. Seven of the Taakoka species, plus one f e r n , a r e r e c o r d e d only f r o m :hat i s l a n d a n 2 not f r o m :he t h r e e r e e f i s l a n d s , bringing the nurnher of s p e c i e s f r o m the l a t t e r down t o 41.
The l i s t i s i n t e r e s t i n g f o r i t s o m i s s i o n s , c o ~ n j ~ a r e c l with o t h e r Cook Island reef islands, p a r t i c u l a r l y those of Aitutaki. Tllere a r e no pandans; Penzplzis acidtrla, e l s e w h e r e ai~undant, i s m i s s i n g ; a n d t h e r e a r e no s p e c i e s of Euphorbiaceae, though on s i m i l a r i s l a n d s on Aitutaki F;U/~horhio clininissonis i s an inl:?rtant c o l n ~ o n e r l t of t h e vegetation.
S o m r a s p e c t s of the f l o r i s t i c s of Rarotonga a r e d i s c u s s e d by Philipsoil (1971).
A l m x t complete s e t s of the s p e c i m ? n s c i t e d a r e de,~?sited in the U.S. National H e r ' o u i t u n , Washington, D.C. and in the h e r b a r i u m of the Botany Division, Dept of Scientific a n d Industrial R e s e a r c h , C h r i s t c h u r c h , New Zealand.
POLYPODIACEAE hspleniziin nidz1.s L -
Oneroa: Sloddavl 211%. Koroniiri: Slo&i?ai*i 2154, I h u o l l i a soliila
(F
f . ) Sw.Oneroa: S l o d i I o ~ t 711.4. Taakoka: Sloddarl. 2767.
CYPERACEAE
Firnbristylis cymosa R. BI.
Motuta.93: Philipson 10364.
PALMAE Cocos nucifeva L.
Motutapu: Stoddart, sight record. Oneroa: Stoddart, sight record. Koromiri: Stoddart, sight record. Taakoka: Stoddart, sight record.
AMARYLLIDACEAE Efippeastvum puniceurn (Lam.) Voss
Taakoka: Stoddavt 2159.
M USACEAE Mzlsa sapienturn L.
Taakoka: Stoldart, sight record.
CASUARINACEAE Casuavina equisetifolia L.
Motutapu: Stoddart, sight record. Oneroa: Stoddm't 2115. Koromiri: Sto,idart, sight record. Taakoka: Stoddart, sight record.
PIPERACEAE Pepevontia leptostachya H. and A.?
Motutapu: Stoddart 2140.
Pepevontia pallida var.
Oneroa: Philipson 10360.
NYCTAGINACEAE Pisonia gvandis R. Br.
Oneroa: Stoddavt 2114.
AIZOACEAE Sesuvium povtulacast^non L.
Matutapu: Stoddavt 2105: Plzilipson 10365.
PORTULACACEAE PovtuZaca lutea Sol. ?
Motutapu: Stoddavt 2106.
LAURACEAE Cassytha filiformis L.
Mstutapu: Stoddart, sight record. Oneroa: Stoddavt 2117. Koromlri: Stoddart, sight record.
HERNANDIACEAE Hevnandia s o m v a L.
Motutapu: Stoddavt 2137. Oneroa: Stoddavt 2124. Koromiri: Stoddavt 2148.
Taakoka: Stoddart 21 64.
CAPEARIDACEAE Cappavis covdifolia Lam.
Motutapu: Stoddavt 2141; Philipson 10361. Koromiri: Stoddavt 2155.
LEGUMINOSAE Canawllia sevicea A. Gray
Motutapu: Stoddavt 2133.
Leucaena insulamna (Lam.) D&.
Motutapu: Stoddavt 2139. Oneroa: Stoddart, sight record.
~Wucuna gig-antea (Willd.)
DZ.
Taakoka: Plzilipson 10351 Sofihova tomentosa L.
Oneroa: Stoddavt 2127.
Vigna mavina (Burm.) M w r .
Motutapu: Stoddavt 2112. Kgromiri: Stoddart 2146. Taakoka: Stoddavt 2165.
Suviana mavitima L.
Oneroa: Stoddavt 2123,
RHAMNACEAE Coldwina asiatica (L.) 0. Ktze,
Oneroa: Stoddavt 2131; Philiyson 10356.
TILIACEAE Tviuiizjelta p?~ocunzDens F o r s t .
Oneroa: Stoddavt 2132. Koromiri: Stoddavt 2147
MALVACEAE Hihisclts sp. (cultivated v a r i e t y )
Taakoka: Stoddavt 21 61.
Hibiscus tiliaceus
L.
M,~tutapu: Sloddavl 2704. Oneroa: Stodd& 2.730. Koromiri: Stoddalfl 2150.
Taakoka: Sloddavt 2166.
Ca?*ica /)apaya L.
Motutapu: I%ilipson I0363
Havvingtonza asiatzca (L.) Kurz Taakoka: Stoddarl 21 72.
CARICACEAE
LECYTHIDACEAE
MYRSINACEAE
CONVOLVULACEAE Ipolizoea 117ac?'antIza it. and S.
Taakoka: St.~ddavt 21 63.
I/~omoen p e s - c a p w e subsp. b l m i l i e n s f s (L.) v . Ooststr.
Motutapu: Stoddm'l 2208. Taakoka: Stoddart, sight record.
BORAGINACEAE Ilelzot?~opiz~iiz anonzalziiiz H. and A.
Motutapu: Stoddarl 21 13.
Toumefovtza ai:gwtea L. f.
Oneroa: Sloddal-t 2128. K a r o m i r i : S t o d r i a ~ l 2152.
VEHBENACEAE Lantana canza?m L.
Oneroa: Sloddart 2122.
Lantana canzava vdr. aculeata (L.) Mold.
Motutapu: Stoddavt 2110. Taakoka: Stoddavl 2160. Koromiri: I'hzlipson 10352.
Staclzyta~[~lzeta uvticifolia S i m s Koromiri: Sloddart 2153.
V i t e x tvzfolia L. var. bicolo?, (Willd.) Mold.
Motutapu: Plzilipson 10362.
RUBIACEAE (;ueltavda speciosa L.
Motutapu: Sloddavl 2136. Oueroa: Sloddavt 2116. Koromiri: Stoddavt 2151;
Philipson 10352.
Movinda c i t v ~ f o lia L .
Motutapu: Stoddavl 2144. Oneroa: Stoddavt 2126. K x o m i r i : Stoddavl 2Z4Y.
Taakoka: Sloddart 2170.
GOODENIACEAE Scaevola taccada (Gaertn.) Roxb.
Motutapu: Sloddavt 2145. Oneroa: Sioddavt 212.9. Koromiri: Stoddart, sight record.
Taakoka: Stoddavt 21 71.
COM POSITAE Bzdens pilosa L.
Koromiri: Stoddavt 2156 I'leplzantofiis mollis HBK.
Mntutapu: S t o d d a ~ ~ t 2143.
Emilia soncllifolia (L.) D C . Matutapu: Stoddavl 2134.
Sonclzus olevaceus L.
Motutapu: Sloddavt 2111, 2138.
U/edelia bzflova (L.) DC.
Motutapu: Stoddavl 2107. Taakoka: Stoddavl 2162.
REFERENCES
Cheeseman, T.F. 1933. The flora of Rarotonga, the chief island of the Cook Group. Trans.
Linn. Soc. London 11. Bot. 6: 261-313.
Philipson, W.R. 1971. Floristics of Rarotonga. Bull. Roy. Soc. New Zealand 8: 49-54.
Wilder, G.P. 1931. Flora of Rarotonga. Bull. Bernice P. Bishop Mus. 86: 1-113.
Figure
3. Reef i s l a n d s o f N g a t a n g i i a Harbour For l o c a t i o n , s e e F i g u r e 2I
ONEROA0 metres 1 0 0
S C A E V O L A T A C C A D A W l T H T O U R N E F O R T I A H I B I S C U S W O O D L A N D C A S U A R I N A W O O D L A N D W I T H S C A E V O L A
COCONUT W O O D L A N D W l T H H I B I S C U S A N D C A S U A R I N A
0
S A N D[=I
I N T E R T I D A L S A N D GRAVELn u e e L E
[1J
B E A C H R O C Ki
