Nezu Phytol.(1996), 133, 217-224

Nickel-accumulating plants from the ancient serpentine soils of

BY R. D. REEVES1, A. J. M. BAKER2, A. BORHIDI3 AND R. BERAZAIN4 Department of Chemistry,Massey University,Palmerston North, New Zealand 2Department of Animal and Plant Sciences, Universityof Sheffield,UK 'Botanical Department,Janus Pannonius University,Pe'cs, Hungary 4Jardz'nBota'nico Nacional, , Cuba (Received 17 July 1995; accepted 15 December 1995)

SUMMARY

Extraordinary uptake of nickel (Ni), reaching concentrations of 0 1-5 0 00, c. 1000 times greater than those usually found in flowering plants, has been observed previously in c. 190 species that grow on Ni-rich serpentine soils derived from ultramafic rocks in various parts of the world. These so-called hyperaccumulators of Ni include c. 50 species from the rich ultramafic flora of New Caledonia and c. 80 species from the Brassicaceae of Mediterranean Europe and Turkey. A study of a limited part (the families Buxaceae and Euphorbiaceae) of the very large ultramafic flora of Cuba has now identified this as the home of at least 80 hyperaccumulators, the largest number yet found in any one country. The more frequent incidence here of this unusual form of plant behaviour is linked to the very long period (c. 10-30 million years) during which some of the Cuban ultramafic substrata are believed to have been continuously available for colonization; the distribution of Ni hyperaccumulators between older and younger ultramafic soils in Cuba mirrors the overall incidence of endemic species in these areas.

Key words: Nickel hyperaccumulators, ultramafic flora, serpentine soils, Buxaceae, Euphorbiaceae.

rarityof any intermediate behaviour towards Ni, i.e. INTRODUCTION most plants on serpentine fall clearly into the Nickel concentrations in leaves of plants normally lie 'normal' (< 100 ,ag g-1 Ni) or 'hyperaccumulator' in the range 0 5-10 ,g g-1 on a dry matter basis. On (> 1000 ,ag g-1 Ni) categories, and (ii) the likelihood serpentine and other magnesium- and iron-rich that such an inordinate uptake of an element known (ultramafic) soils, which generally contain 500- to have deleterious effectson many enzyme systems 5000 ,g g-1 Ni, plants often show slightly elevated must be associated with distinctive detoxification Ni concentrations, in the range 5-100 ,g g-1. How- mechanisms within the plant. Studies of the metab- ever, a small proportion of those plant species that olism of Ni hyperaccumulators are still at an early tolerate ultramafic soils (no more than 1-2 0 world- stage, and the biochemical processes by which the Ni wide) show extreme Ni accumulation, reaching more is absorbed, transported and sequestered are not well than 10000 ,g g-1 (1 %o) in some cases. This type of understood. In the meantime, however, these plants behaviour was firstdiscovered in Alyssum bertolonii should not be regarded as mere curiosities: since in Italy (Minguzzi & Vergnano, 1948). The term most of them are endemic to Ni-rich soils they are hyperaccumulator (Brooks et al., 1977; Reeves, obviously of value as metal indicators, they might 1992) has been applied to plant species in which a Ni have important information to impart about evol- concentration above 1000 ,ag g-1 has been recorded ution in a number of plant genera and families, and in above-ground tissue of plants growing in their their genetic material might be of value in any natural habitat. Detailed studies and analytical work situation where enhanced plant uptake of metals is on plant tissue of specimens from serpentine soils in desired. many parts of the world during the last 20 yr have Several areas of the world where ultramafic rocks revealed that about 190 species (in more than 60 are important have not been studied in any detail differentgenera) behave in this way (Reeves, 1992). from a biogeochemical point of view. These include Justificationfor recognizing hyperaccumulation as Cuba, New Guinea and a number of islands of the a distinct form of plant response comes from (i) the Philippines and Indonesia. The ultramafic flora of 218 R. D. Reeves and others

Habana- Camarioca- Campo Florido San Miguel \ anasi-Corral/Mtmo-- Sierradel \ Nuevo / / Santa Clara ^U Rosario ~~~~~~~Camaguey Cajalbana

20 - SJ~~~~~~~~~~~~~~Hogf

8 ~~~~~~~~~~~~~~~~~~~Moa- Figure 1. Map of Cuba showing (in black) major regions of ultramafic soils. Bars opposite each region represent the total numbers of plant species endemic to each area (stippled bars) and the number of nickel hyperaccumulators found in each (solid bars) Scale at lower left.

Cuba was of particular interestto us for several representedin Cuba (37 species, of which 30 are reasons. Extensive recent work on Cuban phyto- serpentine-obligate);Leucocroton is a genus endemic geography (Borhidi, 1991 a) has emphasized the to Cuba and , 28 of the 30 species being importanceof the Cuban ultramaficsoils as centres endemic to the serpentinesoils of Cuba; another of diversityand endemism. There is a remarkable genus of the Euphorbiaceae, Phyllanthus,has fur- similarityin geography,climate, tropical latitude nished hyperaccumulatorsin other parts of the and economic importance of ultramaficgeology tropics (New Caledonia, Sabah and the Philippine between Cuba in the North Hemisphere and New islands of Palawan and Mindanao) (Kersten et al., Caledonia in the Southern Hemisphere; the large 1979; Jaftr6,1980; Bakeret al., 1992) and is also well number of endemic species (and nickel hyper- representedin Cuba (53 taxa, of which49 are native accumulators) associated with the ultramaficsof and 39 are endemic,26 are serpentine-endemicand New Caledonia have been well documented(Jaffre & nine othersare serpentine-tolerant). Schmid,1974; Jaffreet al., 1976; Brookset al., 1977; Serpentinerocks underlie c. 70 ofthe land area of Jaffreet al., 1979a; Jaffre,Brooks & Trow, 1979b; Cuba. In the lowland-collinebelt of central Cuba Jaffre,1980), and it appeared likelythat because of thereare eightimportant serpentine areas, occupying many similarities of soil type and climate, Ni 2700 km2,between Sierra del Rosario and Holguin hyperaccumulationmight be a featureof the Cuban (Fig. 1). These surfacesare believed to have been ultramaficflora also. A previous study (Berazain, exposed relativelyrecently (Zonn, 1968), giving 1981) of the elemental composition of six Cuban fewerthan 1 million years for the developmentof serpentine plant species from Loma Galindo, their magnesian sialitic and ferraliticsoils and the Matanzas Province, showed that two of them, vegetation they support. By contrast,four other reported as Buxus flaviramea (Britt.) Mathou areas, 4800 km2in total, at the western(Caj'albana) (Buxaceae) and Leucocrotonflavicans Muell. Arg. and eastern(Nipe, Cristal,Moa-Baracoa) extremities (Euphorbiaceae)were hyperaccumulators, with maxi- of the island, have undergone soil and vegetation mum Ni concentrationsof 4500 and 7700,ag g-' developmentover a much longer period, perhaps respectivelyin the dry matter(63 %0 and 11 5 %0 in 10-30 millionyears (Finko, Korin & Formell,1967). the inorganic ash). The specimens of the former The longer period of evolution of these mature species are now identifiedas B. gonoclada (Wr. ex oxisols has led to a much higherfloristic diversity Griseb.) Muell. Arg., whereasthe specimensof the than is presenton the youngersoils. latterare now identifiedas L. angustifolius(Muell. Of the total Cuban floraof 6375 species, approx. Arg.) Pax & Hoffm. half are endemic to the island, and c. 300 of these It appeared that a search for furtherNi hyper- (920 species) are endemicto theserpentine soils. The accumulatorsin the Cuban florashould startwith influenceof thesesoils as a factorin the development the Buxaceae and Euphorbiaceae. Buxus is strongly of such a stronglyendemic flora is thereforewell out Ni-accumulating plants from Cuba 219 of proportion to the land area occupied. The 'young' clear that the genus includes 16 new hyperaccumu- serpentine areas, accounting for 36 % of the total lators of nickel in addition to the one previously serpentine soils, have provided only 140 of the reported. Of the species in Table 1, B. acuminata, B. serpentine endemic species, whereas the 'old' soils brevipes,B. cubana and B. sclerophylla are found on contain 81 00; the other 5 0 are common to both. limestone substrata and show the expected low Ni The number of species endemic to individual concentrations. The plants on serpentine show a serpentine areas is also illustrated in Figure 1. gradation in Ni uptake from low-normal values (2-50 ,g g-1) in species such as B. acunae, B. jaucoensis, B. leoni and B. wrightii,to high-normal MATERIALS AND METHODS values (50-150 ,ag g-1), particularly in the rain forest and mossy forestspecies such as B. marginalis and B. In the course of the present work, leaf fragments muelleriana, and finallyto the 17 hyperaccumulators from c. 120 species of the Buxaceae and Euphor- (> 1000 ,ag g-1). The presence of similar numbers of biaceae that occur commonly or exclusively on non-accumulators and hyperaccumulators among serpentine were screened for Ni accumulation by a the serpentine endemics in this genus should aid in simple semi-quantitative test using filter paper the tracing of evolutionary relationships among the impregnated with dimethylglyoxime (1 00 solution species. Of the 17 hyperaccumulators, eight are in ethanol). In cases of strong positive tests, and in endemic to the serpentines of the Moa-Toa-Baracoa other cases involving serpentine endemic species or area and three others to either the Cristal or Nipe non-serpentine species of genera with a strong areas, whilst three more are found in at least two of affinityfor serpentine, small portions of leaf (from these 'older' eastern regions. The remaining three herbarium specimens or from field collections) were are found on the younger serpentine soils of Holguin analysed by atomic absorption (AA) or ICP-emission (B. heterophylla), Canasi and Camarioca (B. gono- spectroscopy. From herbarium specimens, leaf sam- clada), and Motembo and Santa Clara (B. flav- ples of < 30 mg were generally used, to minimize iramea). damage to the collections. The plant material was weighed into borosilicate test tubes and ashed in a muffle furnace for 4-5 h, the final temperature of Euphorbiaceae 500 ?C being maintained forthe last 2 h. The ash was The genus Leucocroton consists of one species, L. taken up in 5 ml of warm 2 M HCl and the digest leprosus, occurring on limestone in Hispaniola, and finally made up to an appropriate volume (5-20 ml 29 Cuban species. Of the latter, 28 are serpentine depending on sample mass and expected Ni con- endemic, whereas L. microphyllusis a shrub typical centration) with 2 M HCl. The solutions were ana- of dry habitats in limestone karst areas and in dry lysed for nickel and other selected elements either by coastal evergreen forests throughout Cuba (Borhidi, atomic absorption or by plasma emission (ICP) 1991 b). As shown in Table 2, every serpentine spectrometry, using standard solutions prepared endemic species is a hyperaccumulator of Ni, from BDH SpectrosoL 1000 mg I1 atomic spec- whereas the two non-serpentine species, L. leprosus troscopy standards. ICP was employed, when the (sample from ) and L. microphyllus, show sample size permitted, to obtain information about extremely low Ni concentrations. In many cases the the concentrations of 15-20 elements. Solutions Ni concentration exceeds 10000 ,ag g-1 (1 %O). Nickel analysed by both AA and ICP gave agreement to is then, with calcium, one of the two most important within 10 0 for those elements that were determined inorganic elements in the plant. Such a compre- by both techniques; this variation is rather less than hensive occurrence of Ni hyperaccumulation has not that typically found between analyses on different previously been found in a genus of this size, leaves from the same plant specimen. although about 48 taxa of the 170 in the predo- minantly Mediterranean genus Alyssum (Bras- sicaceae) are hyperaccumulators (Brooks et al., RESULTS AND DISCUSSION 1979). The importance of the older Cuban serpentine Buxaceae areas in respect of both speciation and Ni ac- In the Buxaceae, only the genus Buxus is represented cumulation is illustrated by the distribution of in Cuba. This genus of c. 70 species found in Leucocroton accumulator species: 24 of them are temperate Northern Hemisphere latitudes, tropical found only on one or more of the old areas, whereas Africa and the Caribbean, has a major centre of L. virens occurs on both older and younger soils in diversity in Cuba, where 37 species occur; 30 of the eastern half of the island. L. angustifolius is these are believed to be endemic to serpentine soils. widely distributed on the young serpentine areas In the present work, we have analysed specimens of (Habana, Matanzas and Las Villas) and just two 34 of the Cuban species (including all the serpentine other species, L. moncadae (Campo Florido-Habana endemics), with the results shown in Table 1. It is and Camaguiey) and L. anomalus (Holguin), are 220 R. D. Reeves and others

Table 1. Location and nickel concentrations,Buxus species

Species Substrataand locations* Ni concentrationt(utg g-1)

B. acuminata(Griseb.) Muell. Arg. L, Moa-Baracoa 3 B. acunae Borhidi & Mufiiz S, Moa-Baracoa 2 B. aneura Urb. S, Nipe 1450 B. baracoensisBorhidi & Mufiiz S, Moa-Baracoa 1590 B. bisseiK6hler S, Moa-Baracoa 2-57 (2) B. brevipesUrb. L, Sierra de los Organos 1 B. crassifolia(Britt.) Urb. S, Moa-Baracoa 8350-12250 (2) B. cubana (A. Rich.) Baill. L, Guantanamo 17 B. excisa Urb. S, Eastern 2150 B. flaviramea(Britt.) Mathou S, Motembo, Santa Clara 8360 B. foliosa (Britt.)Urb. S, Moa-Baracoa 1320 B. gonoclada(Wr. & Griseb.) Muell. Arg. S, Canasi, Camarioca 2610 B. heterophyllaUrb. S, Holguin 3480-8740 (2) B. historicaBorhidi & Mufiiz S, Moa-Baracoa 4810 B. imbricataUrb. S, Cristal 1940 B. jaucoensisK6hler S, Moa-Baracoa 4 B. leivae K6hler S, Moa-Baracoa 104 B. leoni(Britt.) Mathou S, Cajalbana 6-6 (2) B. marginalis(Britt.) Urb. S, Moa-Baracoa 44-333 (3) B. moana Alain S, Moa-Baracoa 1100-1760 (2) B. muellerianaUrb. S, Cristal 20-133 (2) B. obovataUrb. S, Eastern 51-76 (2) B. olivacea Urb. S, Nipe 2-46 (2) B. pilosula Urb. S, Nipe 4870-9200 (2) B. pseudaneuraK6hler S, Moa-Baracoa 1240 B. retusa(Griseb.) Muell. Arg. S, Eastern 3160-10310 (3) B. revoluta(Britt.) Mathou S, Moa-Baracoa 7870-15630 (2) B. rheedioidesUrb. S, Nipe 11-16 (2) B. rotundifolia(Britt.) Mathou S, Eastern 8-30 (2) B. sclerophyllaK6hler L, Guantanamo < 2 B. serpentinicolaK6hler S, Moa-Baracoa 10410 B. shaferi(Britt.) Urb. S, Eastern 7-140 (4) B. vaccinioides(Britt.) Urb. S, Eastern 25420 B. wrightiiMuell. Arg. S, Cajalbana 14-21(2)

* L, limestone;S, serpentine;serpentine locations shown in Figure 1; 'Eastern' is used forspecies foundon two or all of the threeeasternmost serpentine areas. t Range of values and number of specimensin parentheseswhere more than one has been analysed.

found exclusively on the younger soils. In the Webster 1956-8; Liogier, 1974). We have analysed mountains of the older serpentine areas of eastern 45 specific and subspecific taxa in this genus, not Cuba, many valleys have their own florula with only from Cuba, but also from Puerto Rico and the differentlocal endemics of several genera, including Dominican Republic, where serpentine soils also Leucocroton (Borhidi, 1991 a). In the case of Leuco- occur (Table 3). croton,it seems likely that the capacity for extreme The following observations may be made: (1) nickel accumulation evolved at an early stage in a Species from limestone soils or from nutrient-poor, precursor species of Sect. Leucocroton of the genus, acidic soils show the expected low Ni concentrations. prior to the isolation of populations and other factors (2) The plants from serpentine soils are generally leading to more extensive speciation. clearly divided between hyperaccumulators (25 taxa) Phyllanthus is one of the largest genera in the and non-accumulators, ambiguity only arising in Euphorbiaceae, with over 600 species in tropical cases such as P. incrustatus,which can be found on and subtropical regions of the world. In New gabbroic as well as ultramafic soils with a wide Caledonia it is the genus most strongly represented variety of Ni concentrations. (3) The hyper- on ultramafic soils, which support 76 of the island's accumulators are largely from Subgenus Xylophylla 110 species (Kersten et al., 1979; Jaffreet al., 1987; (Sections Williamia, Thamnocharis and Orbi- T. Jaffre,pers. comm.). Fourteen of these are nickel cularia). In particular, Sect. Orbicularia (14 taxa) accumulators. In Cuba there are 53 species and appears to consist exclusively of Ni hyper- subspecies, about half of which are serpentine- accumulators. (4) Many of the cases of hyper- obligate, while several others occur both on ser- accumulation are extreme (> 1 %o), and the Ni pentine and other substrata (Leon & Alain, 1953; concentrations of 2-6 % in the hybrid P. x pallidus Ni-accumulating plants from Cuba 221

Table 2. Location and nickel concentrations,Leucocroton species

Species Substrataand locations* Ni concentrationt(,ug g-1)

L. acunae Borhidi S, Moa-Baracoa 10140 L. angustifolius(Muell. Arg.) Pax & Hoffm. S, Habana-Campo Florido, Canasi- 6790-19 160 (4) Corral Nuevo L. anomalusBorhidi S, Holguin 13330 L. baracoensisBorhidi ined. S, Moa-Baracoa 2260 L. bracteosusUrb. S, Eastern 11660 L. brittoniiAlain S, Moa-Baracoa 5800 L. comosusUrb. S, Eastern 6470-11740 (4) L. cordifolius(Britt. & Wils.) Alain S, Eastern 2040-19620 (4) L. cristalensisBorhidi ined. S, Cristal 4970-8070 (3) L. discolor Urb. S, Nipe 7670 L. ekmaniiUrb. S, Moa-Baracoa 4610-8550 L. flavicansMuell. Arg. S, Cajailbana 6710-15500 (6) L. incrustatusBorhidi S, Moa-Baracoa 4260 L. leprosus(Willd.) Pax & Hoffm. L, Haiti 3 L. linearifoliusBritt. S, Moa-Baracoa 13310-27240 (6) L. longibracteatus Borhidi S, Moa-Baracoa 3850 L. microphyllus(A. Rich.) Pax & Hoffm. L, Cienfuegos,Las Villas < 6 L. moaensisBorhidi S, Moa-Baracoa 9770-15510 (4) L. moncadaeBorhidi S, Habana-Campo Florido, 15330 Camagiuey L. obovatusUrb. S, Cristal 5070-9980 (3) L. pachyphylloidesBorhidi S, Moa-Baracoa 5800-18050 L. pachyphyllusUrb. S, Moa-Baracoa 693-9220 (3) L. pallidus Britt. S, Moa-Baracoa 10760 L. revolutusWright ex Sauv. S, Cajalbana 8910-17 240 (4) L. samekiBorhidi S, Moa-Baracoa 13080 L. saxicola Britt. S, Nipe 10820-18480 (2) L. stenophyllusUrb. S, Nipe 12090-24500 (2) L. subpeltatus(Urb.) Alain S, Eastern 13890 L. virensGriseb. S, Camaguey, Holguin, Eastern 5630-24 360 (2) L. wrightiiGriseb. S, Eastern 7410-12600 (4)

* L, limestone;S, serpentine;serpentine locations shown in Figure 1; 'Eastern' is used forspecies foundon two or all of the threeeasternmost serpentine areas. t Range of values and numberof specimensin parentheseswhere more than one has been analysed. are among the highest ever recorded in whole-leaf the West, and none is exclusively found on the tissue of any plant species. It may be noted that younger soils. One species P. discolor, is common to among the strongly Ni-accumulating species of the the younger soils and the older western soils of small genus Bornmuellera (Brassicaceae) of Greece Cajalbana, whereas P. orbicularishas spread through and Turkey, the highest Ni concentrations (> 3 O%) the island, probably from east to west. Although are reached in the hybrid B. xpetri (Reeves, Brooks such a spread could have taken place no later than & Dudley, 1983). (5) Of the species analysed from the Oligocene along a continuous serpentine axis that serpentine and other substrata in the Antilles beyond might have existed at that time, it might have Cuba, only P. nummularioidesfrom the Sierra Prieta occurred more recently across the discontinuous and Loma Peguera in the Dominican Republic was a serpentine blocks through the agency of birds, Ni hyperaccumulator. (6) In the examination of insects or animals (Borhidi, 1991 a). specimens from serpentine soils in this large and In the speciation mechanism of island floras, and taxonomically difficultgenus, Ni accumulation could especially in Cuba, genetic drift might play an be used as an aid to identification, even in the field, important role. The process is conditioned by the as it is a character that is usually clear-cut and easily many small-flowered species pollinated by insects of determined. (7) As in the case of Buxus, the microscopic size within the frame of a highly diverse distribution of the serpentine species between ac- vegetation, which the serpentine scrubs usually are. cumulator and non-accumulator categories might be Generally, these insect populations are not capable of value in determining taxonomic, evolutionary and of flying long distances and, to avoid strong winds chorological relationships. (8) As in Leucocroton and blowing from the sea, they stay in the shelter of Buxus, the Ni-accumulating Phyllanthus species are plants. Thus, gene flow between remote plant centred on the older serpentine soils. Of the 24 populations is difficultor impossible. This barrier Cuban hyperaccumulators, 20 are exclusive to the must have contributed significantlyto the isolation older soils of the East, two are exclusive to those of of populations subject to genetic drift,and resulted 222 R. D. Reeves and others

Table 3. Location and nickel concentrations,Phyllanthus species

Species Substrataand location* Ni concentrationt(,ug g-1)

P. acuminatusVahl L, Santiago de las Vegas, Habana < 17 P. amarusSchum. & Thonn. S, Maricao, Puerto Rico 12 P. berteroanusMuell. Arg. L, Cordillera Septentrionale,Dominican < 25 Republic P. brachyphyllusUrb. L, Barrancon,Dominican Republic 30 P. caroliniensisWalt. ssp. saxicola (Small) L, Baracoa; Camagiuey < 7-235 (2) Webster P. chamaecristoidesUrb. ssp. S, Nipe 18530 chamaecristoides ssp. baracoensis(Urb.) Webster S, Eastern 3400-31 750 (11) P. chryseusHoward S, Moa-Baracoa 10790-13790 (4) P. cinctusUrb. S, Moa-Baracoa 11510-21870 (4) P. comosusUrb. S, Eastern 9340-19380 (4) P. comptusWebster S, Cajalbana 7260 P. cristalensisUrb. S, Cristal 4200-8750 (5) P. cuneifolius(Britt.) Croiz. S, Susua, Puerto Rico 24 P. discolorPoepp. ex Spreng. S, Cajalbana, Habana-Campo Florido, 13670-31490 (5) Canasi-Corral Nuevo, Camarioca-San Miguel, Santa Clara P. echinospermusWr. ex Sauv. S, Cajalbana 122 P. ekmaniiWebster S, Nipe 12060-19060 (2) P. epiphyllanthusL. ssp. dilatatus L, Baracoa 3 (Muell. Arg.) Webster P. excisusUrb. S, Eastern 27-442 (2)y P. formosusUrb. S, Eastern 7400 P. incrustatusUrb. G, S, Eastern 10-1582 (5) P. juglandifoliusWilld. Various, (Cuba, Puerto Rico) < 3 (2) P. junceusMuell. Arg. L, Pinar del Rio < 9 P. micranthusA. Rich. A, Guantanamo 39 P. microdictyusUrb. S, Moa-Baracoa 4950-19 750 (7) P. mirificusWebster S, Moa-Baracoa 4480-7690 (4) P. myrtilloidesGriseb. ssp. alainii Webster S, Cristal 14330 ssp. erythrinus(Muell. Arg.) Webster S, Moa-Baracoa 16 940-33 240 (5) ssp. myrtilloides S, Eastern 8490-9970 (2) ssp. shaferi(Urb.) Webster S, Eastern 7910-21 710 (2) ssp. spathulifolius(Griseb.) Webster S, Eastern 5780-8900 (2) P. nummularioidesMuell. Arg. S, Loma Peguera & Sierra Prieta, 12240-22930 (4) Dominican Republic P. nutansSw. ssp. grisebachianus(Muell. S, Eastern < 3 Arg.) Webster P. orbicularisH.B.K. S, Pan-Cuban 4140-10 950 (7) P. pachystylusUrb. S, Eastern 27-269 (3) P. xpallidus (Wr. ex Griseb.) Webster S, Caj'albana 15390-60170 (4) (P. discolorx P. orbicularis) P. pentaphyllusWright ssp. Pentaphyllus S, Susua, Puerto Rico 9 ssp. polycladus(Urb.) Webster S, Susua, Puerto Rico; 94 L, Guanica, Puerto Rico < 32 P. phlebocarpusUrb. S, Eastern 4890-19400 (3) P. procerusWright S, Santa Clara, Las Villas < 15 (2) P. pseudociccaGriseb. S, Eastern 9460-22670 (4) P. scopulorum(Britt.) Urb. S, Moa-Baracoa 13650-21 930 (2) P. subcarnosusWright L, SL, Pinar del Rio 2-16 (3) P. urinariaL. S, Maricao, Puerto Rico 4 P. williamioidesGriseb. S, Moa-Baracoa 232-18100 (2)

* A, andesite; G, gabbro; L, limestone;S, serpentine;SL, slate; serpentinelocations shown in Figure 1; 'Eastern' is used for species found on two or all of the three easternmost serpentine areas of Cuba. t Range of values and number of specimens in parentheses where more than one has been analysed.

in the formation of high numbers of vicarious to concentrations of other transition metals such as endemics, as in the case of all three genera discussed zinc and cobalt, since accumulator species of these above (Borhidi, 1982, 1991a). elements are also well known. We found no unusual Some specimens in this study have been subjected accumulation of Zn (which is not in any case present to a more complete analysis, with particular attention at abnormal levels in ultramafic soils), and only Ni-accumulating plants from Cuba 223 occasional noteworthy elevated Co concentrations on several areas have been apportioned in equal (100-800 ,ug g-1) in some specimens of several of the fractions to the relevant areas. It is clear that the Ni hyperaccumulators such as Buxus historica, distribution of Ni hyperaccumulators parallels Phyllanthus scopulorum, P. myrtilloidessubsp. ery- closely that of Cuban serpentine endemism gen- thrinus, Leucocroton cordifolius, L. cristalensis, L. erally. discolor, L. moaensis, L. saxicola, L. stenophyllusand We have thus established in an investigation of L. wrightii. only a small part of the Caribbean ultramafic flora, Further Ni hyperaccumulators have been found in i.e. the two families from the Order Euphorbiales, other smaller genera of the Euphorbiaceae repre- that there are more Ni-accumulating plant species in sented on serpentine in Cuba, Puerto Rico and the Cuba (80) than have been found in any other country Dominican Republic (Ni concentrations in ptgg-1 in in the world, exceeding the 53 species found in New parentheses): Bonania emarginata Wright ex Griseb. Caledonia. The 10-30 million year period of ex- (429-1620); B. nipensis Urb. & Ekm. (1850); B. posure of the older Cuban ultramafics, comparable suborbiculata Borhidi & Urbino (1760); Euphorbia in age to those of New Caledonia, would appear to cubensis Boiss. (2860-5840); E. helenae Urb. subsp. have been a major factor influencing both the helenae (3160-4430); E. helenae subsp. grandifolia evolution of a richly endemic serpentine flora and the Borhidi & Muniiz (1980-9340); Gymnanthesrecurva emergence of Ni hyperaccumulation in so many Urb. (2240-4070); Sapium erythrospermum(Griseb.) plant genera and species. This situation contrasts Muell. Arg. (1000); Savia clusiifolia Urb. strongly with that of higher latitudes in both (1600-2940); S. cuneifolia Urb. (4-4890); S. macu- hemispheres where recent glaciation has resulted in lata Urb. (343-4660). The data on Savia might a much shorter time scale for continuous floristic need to be reassessed in the light of a re-classification development, and where both serpentine endemism currently in progress (P. Hoffmann, pers. comm.). and Ni hyperaccumulation are relatively uncommon. No exceptional Ni uptake was found in serpentine occurrences of species of Acidocroton, Alchorneopsis, ACKNOWLEDGEMENTS Chaetocarpus, Croton, Ditta, Drypetes, Hyeronima, Moacroton, Pera or Platygyne. The authors thank the Directors and other staffof the Attention should be drawn to one further re- followingHerbaria, who kindlyprovided information and markable observation on the Cuban Euphorbiaceae. samples for analysis: The New York Botanical Garden; The latex of Euphorbia helenae subsp. grandifolia, Natural History Department, Institute of Jamaica, Kingston; Botanical Department,University of the West exuded copiously when leaves are removed or small Indies, Kingston,Jamaica; Academy of Sciences, Havana, branches broken, becomes greenish upon exposure Cuba; JardinBotanico Nacional, Havana, Cuba; Natural to the atmosphere. A sample of the latex, afterdrying History Museum, Budapest, Hungary. We are also at 4 ?C, was found to contain 3 09 00 Ni, 0 37 00 Ca, indebted to Prof. E. K6hler and Mrs P. Hoffmann, 0 310 Mg, 0 14 % Na, 0 07 o K and 0 04 o Co; Ni Museum furNaturkunde, Humboldt Universitat,Berlin, accounted for c. 75 % of the total mass of the metallic forsamples and taxonomicinformation. RDR and AJMB elements present. Leaf specimens of the same plant wish to acknowledgefinancial support for fieldwork from contained 0 2-0 9 00 Ni, 1 1-1 3 00 Ca, 0-4-0 5 00 Mg Dupont Central Research and Development, Newark, and 04-060% K. The latex is thus considerably Delaware, USA. A Small Ecological Project Grant was enriched in Ni relative to the leaf, as has been provided by the British Ecological Society (to AJMB). staffof the observed previously in Sebertia acuminata (Sapo- Assistancein the fieldin Cuba was providedby Jardin Botanico Nacional, Havana, and the Instituto taceae) from New Caledonia (Jaffreet al., 1976) and Superior Minero Metalurgico,Moa. 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