palms bayton et al.:re-examination of borassus volume 47(4

PALMS Bayton et al.: Re-examination of Borassus Volume 47(4) 2003

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A Re-examinationof Borassus inMadagascar

ROSS P. BAYTON

School of Plant Sciences, University of Reading, Whiteknights, PO Box 221, Reading, Berkshire, RG6 6AS, UK,[email protected]& Royal Botanic Gardens,Kew, Richmond, Surrey, TW9 3AB, UK

CALEB OBUNYALI

East African Herbarium, National Museums ofKenya, PO Box 45166, Nairobi, Kenya

AND

ROLLAND RANAIVOJAONA

Herbier, DépartementBotanique, Parc Botanique etZoologique de Tsimbazaza, B. P. 4096, Antananarivo 101, Madagascar

Due to the lack of adequate herbarium material, the taxonomic status of the two endemic

species of Borassus in Madagascar has remained uncertain. This account reports the

preliminary conclusions of a study aiming to resolve the issue, utilizing newly-collected

specimens from Madagascar and Kenya.

PALMS 47(4): 206–219

1. Female Borassus aethiopumgrowing by the Tana River inCoast Province, Kenya. Photoby J. Dransfield.

The taxonomy of African Borassus L. (Cory-phoideae: Borasseae) has been the subject of somecontroversy since the first African species, Borassusaethiopum (Fig. 1), was described by von Martiusin 1838. Warburg was one of several authors todisagree with Martius. He sank B. aethiopum,recognizing it only as a variety of the AsianBorassus flabellifer (Warburg 1895).

However, almost 20 years later, the eminent palmbotanist Beccari, published a monograph of thegenus, in which he recognized Borassus aethiopumand B. flabellifer as separate and distinct species(Beccari 1914). In addition, he described a newspecies, Borassus deleb, from the Sudan, and alsorecognized two varieties within B. aethiopum: B.aethiopum var. bagamojensis from East Africa andB. aethiopum var. senegalensis from West Africa. In1986, Dransfield sank Beccari’s new species andvarieties recognizing only Borassus aethiopum Mart.in East Africa (Dransfield 1986a).

The taxonomy of Borassus in Madagascar has beenno less contentious. Borassus madagascariensis wasfirst published by Bojer in 1837, thus predating B.aethiopum by one year. However, no type was citedand there was no description of the plant, thusrendering the name illegitimate. In 1907, theFrench botanists Jumelle and Perrier de la Bâthiedescribed the species as a variety of Borassusflabellifer, but later elevated it to species-level inPalmiers de Madagascar (Jumelle & Perrier de laBâthie 1913). They provided a full description ofthe plant (but no type), and so, inadvertently,validly published the species, which they hadattributed to Bojer. This is the reason why Borassusmadagascariensis (Jum. & H. Perrier) Bojer ex Jum.& H. Perrier revels in such a long author citation!

In addition to B. madagascariensis, Jumelle andPerrier de la Bâthie described a second endemicspecies of Borassus. The new species, which theynamed Borassus sambiranensis, was restricted tothe area between the Sambirano and Ifasy riversin the north-west of Madagascar (Jumelle & Perrierde la Bâthie 1913).

Palmiers de Madagascar (1913) and the later palmvolume of the Flore de Madagascar et des Comores(Jumelle & Perrier de la Bâthie 1945) weresuperseded by The Palms of Madagascar (Dransfield& Beentje 1995), which described all of the speciesand genera of palms on the island, yet Borassusremained enigmatic. The limited herbariummaterial available to the authors allowed for onlya preliminary judgment as to the taxonomic statusof Borassus. In their opinion, there were fewmorphological characters, which could be used todistinguish reliably either of the Madagascar taxafrom B. aethiopum in mainland Africa (Dransfield& Beentje 1995).

Taxonomic confusion

Borassus is one of the most widely-distributed ofpalm genera, and can be found from the Atlanticcoast of Africa in the west to New Guinea in theeast. The continuing confusion over speciesdelimitation is well demonstrated in thetaxonomic history of the African taxa. Specieshave been recognized, then reduced to varieties,then sunk or recognized again as species, and thereare a number of factors that have contributed tothis uncertainty. There are considerable logisticalproblems associated with collecting Borassus. Allmaterial must be collected from a crown that maybe 20 meters or more above the ground. The single


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2. Previous herbarium collecions from eastern and southern Africa (left). Collecting sites in Madagascar (center) andKenya (right).

stem is smooth and ventricose with a belly whichcan reach a girth of over two meters. This prohibitsmany climbing techniques. The stems of younger,shorter palms are covered in old leaf-bases, whichare armed with spines. Where access is possible,the material which is gathered is heavy anddifficult to dry in the field. As a final deterrent,Borassus is dioecious, and so access must be gainedto the crown of another individual of the oppositegender in order to collect complete material of aspecies.

Throughout much of its range Borassus iscommon, and very few collectors, even those whospecialize in collecting palms, will make the effortrequired to collect a complete specimen of a large,common, widespread palm. Therefore, there areseveral parts of the range where there are few orno specimens in existence. In particular,Madagascar, West Africa and Indonesia are poorlysampled.

Another problem that has led to confusion in thetaxonomy of Borassus is the lack of typespecimens. The designation of a particularherbarium specimen as ‘type’ of a name onlybecame obligatory in 1958. Many earlier authorsdid not specify a type specimen when publishing

new taxa and the type must be inferred. Thedescription of Borassus aethiopum was based on aspecimen collected by Peter Thonning in Ghanabut this has since been lost (Hepper 1976). Jumelleand Perrier de la Bâthie did not cite specimenswhen publishing Borassus madagascariensis and B.sambiranensis and no suitable material could befound in their collection in Paris.

Collecting in the field

The aim of this study is to assess the status of thespecies of Borassus in Madagascar on the basis offield observations and herbarium material. To thatend, an expedition to Madagascar was organizedin conjunction with the Parc Botanique etZoologique de Tsimbazaza in Antananarivo.Fieldwork was completed by RPB and RR in March2003. Herbarium material of B. aethiopum wascollected during a prior expedition to Kenya,organized in conjunction with the NationalMuseums of Kenya. This fieldwork was completedby RPB and CO in October 2002. The collectingsites of all specimens are shown in Figure 2.

The major aim of the fieldwork was to collect asmuch herbarium material as possible. Fieldworkalso allows the investigator to observe the plantsin the living state, photograph specimens to


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3 (left). Caleb collecting a DNA sample of Borassus aethiopum outside Mazeras town, near Rabai, Kenya. 4 (right).Juvenile specimen of B. aethiopum in the Shimba Hills, Kenya. The dark petioles armed with large erose spines arecharacteristic of the species.

preserve perishable characters, and to collectadditional data on distribution, ecology andconservation status. A secondary aim of thefieldwork was to collect plant samples for DNAextraction and analysis. This is often difficult orimpossible to do from preserved herbariumspecimens as DNA degrades with age, and withexposure to light and certain chemicals used aspreservatives. The DNA samples collected in Kenyaand Madagascar form part of a continuing projectby RPB to investigate evolutionary relationships intribe Borasseae.

KenyaBorassus aethiopum in Kenya (Fig. 1) is primarilyrestricted to the humid coastal region, though ithas been recorded near the Somali border in thearid north, and on the north shore of Lake Victoria(Beentje 1994). Three collection sites were chosenin Coast Province and these sites variedconsiderably. The first, Rabai (03º56’S, 39º33’E)(Fig. 3), was dominated by large areas of cultivatedcoconut and, though inconspicuous, Borassusappeared to be numerous. Despite the densecanopy of palm leaves above, several crops


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5. The ShimbaHills populationof B. aethiopumnear Mivumoni.

6. Secondaryschool inMivumoni. Thesign shows B.aethiopum withthe characteristicbulging stem,and two AfricanFish Eagles(Haliaeetusvocifer). TheSwahili on thesign translates as“Endeavors bringsuccess.”

including maize, cassava and pineapple weregrowing beneath. Borassus was generally ignoredwith the exception of one mature tree in whichthe trunk had forked producing two crowns. Thisspecimen was venerated by village elders. In Asia,Borassus flabellifer is widely cultivated as almost allparts of the palm can be used for some purpose.This did not appear to be the case with B.aethiopum in Kenya, and the villagers in Rabaireported that the only useful part of the plant wasthe old leaf sheaths which made good firewood.

Further south by the Tanzanian border is theShimoni peninsula (04º36’S, 39º23’E). Here it ispossible to see five of Kenya’s seven native palmspecies. Borassus aethiopum occurs in the companyof Hyphaene coriacea, H. compressa, Phoenix reclinataand Elaeis guineensis. Domesticated Cocos nuciferais also present. The topography of the peninsulais deceptive. The palms (and Borassus in particular)are visible for long distances over the scrubvegetation. However, the terrain is uneven withcoral limestone protruding from the soil, and thevegetation is dominated by two-meter tallHyparrhenia rufa grass and introduced Lantanacamara. A quick stroll towards some nearby palmsrapidly becomes an unpleasant three-hour trek.

The third site was in the Shimba Hills althoughmost of the palms lay outside the boundaries ofthe Shimba Hills National Reserve (Figs. 4, 5). Thispopulation is centered on the village of Mivumoni(04º24’S, 39º24’E), which is named after Borassus(or mvumo in Swahili) (Fig. 6). At this site, B.aethiopum grows in small river valleys and on someslopes to an altitude of 300 m. Despite the localconnection with the palm, Borassus is unpopular.As a wild plant it has evolved several mechanismswhich protect it from herbivory and fire damage,including spiny petiole margins and a longcotyledonary axis that buries the seedling in thesoil. However, these survival mechanisms alsomake the palm difficult, if not impossible, toeradicate from agricultural land. The palms arerarely felled as the tough fibrous stem can causeconsiderable damage to axes and saws. A felledpalm trunk is also a significant obstacle in its ownright. The population of B. aethiopum in theShimba Hills was the largest of the threepopulations observed in Kenya.

A fourth population of B. aethiopum is known tooccur on the Tana River, near the town of Garsen(02º16’S, 40º07’E), and specimens were collectedthere by John Dransfield in 1975 (Fig. 1). However,the recent civil war in neighboring Somalia has,to some extent, spilt over into this part of Kenyaand it was decided not to visit this population forsafety reasons.

Madagascar

Borassus in Madagascar is thought to be entirelyrestricted to the west coast of the island. Borassusmadagascariensis occurs in several river valleys inToliara and Mahajanga Provinces while B.sambiranensis is restricted to the Sambirano Regionin Antsiranana Province. To enable both speciesto be collected, two excursions were organized –the first to the city of Mahajanga and the secondto Ambanja on the Sambirano River.

The last part of the road trip from Antananarivo(Tana) to Mahajanga follows the course of theBetsiboka River. The river, together with the coastaltowns of Marovoay and Mahajanga were describedby Bojer as the type locality for B. madagascariensis(Bojer 1837). The only herbarium material ofBorassus from this part of Madagascar (collected in1995 by Dr Larry Noblick of the MontgomeryBotanical Center, Miami, USA) was collected nearto the coast. Therefore, we were surprised to finda population of Borassus in the town ofMaevatanana (16º56’S, 46º49’E), some 250 kminland (Figs. 7, 9, 11). The palms could be foundgrowing in gardens and on the street but appearedto be ‘tolerated’ rather than cultivated. Wereturned to the town on our journey back to Tanato make a collection.

We found several isolated groups of B.madagascariensis along the course of our journey,including at Ankijabe village (16º24’S, 46º46’E)(Fig. 8), Lake Amboromalandy (16º08’S, 46º45’E)and at the Ampijeroa Forestry Station (16º18’S,46º49’E) of Ankarafantsika National Park.However, the most significant population was inand around the town of Marovoay (16º06’S,46º41’E) (Fig. 10). Borassus madagascariensis (ordimaka in the local Sakalava language) wasgrowing in fields and gardens, but also in thecenter of town. Seedlings could be found growingthrough cracks in the sidewalk and in abandonedhouses. Perhaps the difficulties involved inremoving these palms (as discussed earlier) are thereason why they remain in public places. However,none of the sites where dimaka was found was freefrom human interference. Perhaps Borassusmadagascariensis is a colonizer of disturbedhabitats. Another possibility is that local peoplehave influenced the distribution of this palm,though the Malagasy we encountered hadrelatively few uses for the palm.

Our second excursion took us by plane to theisland of Nosy Bé off the north-west coast ofMadagascar. From there we went by boat to thetown of Ambanja (13º43’S, 48º23’E). Only twomodern specimens of B. sambiranensis had beencollected: one by Dr. George Schatz (Missouri


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Botanical Garden) in 1988 near Ambanja; theother by Dr. Henk Beentje in 1992 nearMaromandia. However, neither of these sites couldbe located.

There was some difficulty in identifying the palmwhen talking with local people. The name dimakaused further south was not always understood andwe were often led on long detours only to find therelated Bismarckia nobilis. Our first encounter withB. sambiranensis occurred during one of thesedetours when we noticed a juvenile palm in anabandoned field (Figs. 12, 13). It had heavily-armed petiole margins and was reminiscent ofjuvenile specimens of B. aethiopum in Kenya. Ourlocal guides described it as satranbe which is theSakalava word for Bismarckia. We spent seven dayssearching for Borassus both to the north and southof the Sambirano River. Our only other find wasof a pair of male palms hidden within a group oftrees.

On our return to Nosy Bé we discovered two verytall adult Borassus palms in the center of Hell-Villetown (13º24’S, 48º16’E)(Fig. 14). Both weregrowing in prime locations with a male tree infront of the mayor’s office, and a female treeoutside the central police station. This providedour only opportunity to collect material of thefemale palm, though due to its incredible height,we had to be satisfied with old flowers andinfructescences from the ground beneath. Anadditional bonus was the discovery of a malespecimen of Lodoicea maldivica flowering in thegardens of a Catholic mission (Fig 15). We weregranted permission to make a collection whichwas fortuitous as no male herbarium material ofthis species exists at either Kew or Tana.

Collecting Methods

It is essential when making herbarium specimensto collect fertile material, and with many tallpalms, dead inflorescences are collected from theground beneath. However, access to the canopy

allows fresh material to be collected and this ispreferable when pollen and DNA samples arerequired. In Kenya, it was hoped that the treescould be climbed using a rope strop and climbingirons (spikes). However, the large belly of the stemprecluded access above that level and the hardstem allowed minimal penetration by the spikes.The decision was taken to fell one male and onefemale tree at each location. There are obviousconservation implications when felling largepalms but it was considered that the populationswere of sufficient size to allow this. Permissionwas granted by the owners and the trees for fellingwere selected by them.

Access to the crown allowed several completeduplicates of each specimen to be produced. Thematerial was preserved using the modifiedSchweinfurth method (see Dransfield 1986b). Leafmaterial for DNA extraction was collected fromthe sword leaf and dried in silica gel. Fieldwork inKenya coincided with the fruiting season and themany large fruits of the female trees weremeasured.

The methods employed to collect both herbariumand DNA samples in Madagascar differedconsiderably from those used in Kenya. Bothspecies of Borassus are threatened and are listed bythe IUCN (2002). Therefore a different collectionstrategy was adopted. A ten-meter long pole-sawwas used to collect material from the canopy. Thisnecessitated locating smaller adult palms orfinding a vantage point, such as a tree or hill, fromwhich the canopy could be reached. Wherepossible, several duplicate specimens wereproduced and they were preserved using theSchweinfurth method.

A different approach was required to collectmaterial for DNA extraction as the newer leavesin the center of the canopy were beyond reach.Therefore, root-tips were collected, splitlongitudinally, and dried in silica gel. The root-tipswere often visible emerging from the stem just


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Table 1. Diagnostic characters for Borassus in Madagascar & East Africa.

Character B. madagascariensis B. sambiranensis B. aethiopum Petiole Color Yellow along entire Yellow-orange distally, Yellow distally,

length brown proximally. brown proximally.

Petiole Armature Spines short (0.1–0.8 Spines long (1.2–2.4 Spines long cm), erose to serrate cm), erose (Fig. 18) (1.2–2.8 cm), erose(Fig. 18) (Fig. 18)

Fruit Apex Shape Pointed. Flattened or depressed Flattened or depressed

Fruit Size 16–19 cm long × 7–13 cm long × 8–15cm long ×15–16 cm diameter 5–11 cm diameter 7–11 cm diameter

above the soil surface. In other cases they couldbe located in the leaf litter, or be found emergingfrom eroded soil surfaces. Preliminary studiessuggest that DNA extracted from roots is notcontaminated with foreign DNAs such as those ofmycorrhizal fungi.

Preliminary Findings

1. Borassus madagascariensis (Jum. & H. Perrier)Bojer ex Jum. & H. Perrier

Morphology. Massive, solitary dioecious palm to 20m tall. Old leaf bases remain attached to the trunkuntil the palm reaches maturity and then theyfall away leaving distinctive scars on the stem.

Stem is ventricose reaching 80cm diameter at itswidest point. There are 16–23 green leaves in thecanopy and these are costapalmate with a radiusof up to 125 cm. The petiole is yellow in coloralong its entire length, up to 240 cm long, and 6–9cm wide at the hastula. The petiole margins arearmed with short black spines that are erose orserrated in shape. Each leaf has between 100 and130 segments and these are 8 cm wide with smallbrown scales on the surface. Brown indumentumcan be found on younger leaves, particularly nearthe hastulae. The male inflorescence is up to 150cm long and branches to two orders. The tubularbracts are green and leathery with some brownindumentum. The lower empty bracts have hard,


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7. Borassusmadagascar-iensis, a femaletree in the townof Maevata-nana.

8. Borassusmadagascari-ensis, a maletree in flowernear the villageof Ankijabe.

acuminate apices while the upper bracts havemore rounded apices. Inflorescence branchesterminate in 1–3 rachillae which are dark brown,up to 40 cm long and 3 cm diameter. Malerachillae are covered in overlapping scales withinwhich are pits containing the male flowers. Maleflowers are arranged in a cincinnus with 8–12flowers, emerging from the pit one at a time.Female inflorescences are unbranched and to 120cm long. There are 8 empty bracts with brownindumentum and woody acuminate apices. Theflower-bearing section of the inflorescence is upto 90 cm long with 7–15 flowers. Female flowersare large and solitary. Fruits are green to yellow incolor with a waxy surface. They are up to 19 cmlong and 16 cm diameter, and contain 1–3pyrenes. The pyrenes are also large (8.2–12.1 cmlong × 8.6–12.0 cm diameter) and some have adistinctive longitudinal crest.

Distribution. Western Madagascar: Mahajanga andToliara Provinces. Endemic.

Habitat. Patchy distribution, particularly alongriver valleys in gallery forest at elevations of 0–60m above sea level. Along the Betsiboka River occursprimarily in disturbed areas, including farmland,gardens and urban areas.


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9 (top left). In the town of Maevatanana, a male B.madagascariensis planted in the front garden of theMayor’s office. 10 (top right). A close-up view of thepetioles of B. madagascariensis showing their yellow colorand small marginal spines. This photo (of a juvenilepalm) was taken in the town of Marovoay. 11 (bottomright). A juvenile specimen of B. madagascariensisgrowing on the street in the center of Maevatanana.

Ecology. One of the most memorable aspects ofcollecting B. madagascariensis is the noise of birdsin and around the canopy. The palm is selected bythe Sakalava Weaver bird (Ploceus sakalava) thatattach their woven grass nests to the tips of theleaflets. The birds nest colonially, and hundreds ofold and new nests festoon the palm like pendantChristmas decorations. Borassus is particularlysuitable as a nest site as the massive solitary stemmakes access into the canopy difficult orimpossible for land-bound predators and palmcollectors alike! Aerial predators are quickly spottedas, at any one time, there are hundreds of birds inor around the canopy.

Nothing is known about the pollination ofBorassus. In his extensive review of palmpollination studies, Henderson (1986) reports nospecific information on the pollination ofborassoid palms. Recently, Gerlach (2003) reportedthat flies (and in particular Ethiosciapus bilobatus,Dolichopodidae) were the most likely pollinatorsof Lodoicea maldivica, though geckos could not beruled out. Observations of B. madagascariensisshowed that the only insect species attracted to themale flowers was the honeybee (Apis mellifera).An indigenous subspecies of honeybee (A. melliferaunicolor) has been described in Madagascar butother subspecies may have been introduced(Ratsirarson & Silander 1996). At the time of study,the female trees were in fruit and so there were nofemale flowers to investigate. Other animal speciesnoted on the male flowers include day geckos(Phelsuma dubia) and a chameleon (Furciferoustaleti), although the latter is entirely an insectpredator. Gerlach noted that Phelsuma geckos fedon both the nectar of L. maldivica and on insectsvisiting the flowers. The inflorescences of B.madagascariensis were not observed at night andso nocturnal insects and bats cannot be discountedas potential pollinators.

An additional factor which may influencepollination is the sex ratio. In B. madagascariensis,this was observed to be 2 males:1 female. Apopulation of B. aethiopum observed by RPB inMalawi had a sex ratio of 1:1, as did threepopulations of the same species in Ivory Coast(Barot & Gignoux 1999). However, a fourth Ivorianpopulation had significantly more male trees,while the population of Lodoicea on Praslin(Seychelles) was shown to comprise 64.3% males.This was attributed to an increased mortality in thefemale trees (Savage & Ashton 1983).

At present no information is available on seeddispersal of B. madagascariensis. The large terrestrialherbivores identified by Zona & Henderson (1989)as dispersal agents for B. aethiopum are not present

in Madagascar. However, fruit bats in the generaPteropus and Eidolon are represented on the island(Garbutt 1999) and have been identified asdispersal agents of palms (Zona & Henderson1989). It seems unlikely that even the largest ofbats could carry the fruits of Borassus far from thetree, and the fruits of B. madagascariensis may bethe largest in the genus. One possibility is thatthe seeds were dispersed by an extinct animal.Among the mammals, three species ofhippopotamus and a number of lemurs havebecome extinct. The largest of the extinct lemurs,Archaeoindris fontoynontii, weighed upwards of 200kg but has only been found at one site in thecentral plateau (Garbutt 1999). The three extinctlemurs in the family Archaeolemuridae weresmaller, and adapted to a primarily terrestrial life,similar to modern day baboons (Garbutt 1999).The extinct elephant birds (family Aepyornithidae)may also have consumed palm fruits (Dransfield& Beentje 1995). However all theories involvingextinct animals remain speculative. Anotherpossibility is that the fruits disperse themselves.Their large size may allow them to travel fartherfrom the tree when they fall. The fruits may becarried by rivers and the sea though no evidenceexists to show whether the seeds are damaged byimmersion in water. When the close proximity ofall populations of B. madagascariensis to humansettlements is considered, it is impossible to ruleout people as seed dispersal agents.

Conservation Status. The largest population of thisspecies was at Marovoay. Although 35 adult palmswere observed from the road, local people told usof additional trees further back into the forest. Weobserved just over 90 juvenile palms although thisis probably an underestimate as thick vegetationeasily conceals small seedlings. The otherpopulations ranged in size from 17 adults(Maevatanana) to a single adult (Ankijabe). Noadults and only four juvenile palms were found atthe Ampijeroa Forestry Station. There appear to befew threats to the populations of B.madagascariensis in Mahajanga Province. Thepalms were not exploited for any products andregeneration was obvious and abundant at all siteswhere more than one adult palm was present. Thestatus of B. madagascariensis in Toliara Province isunknown. Borassus madagascariensis is listed asvulnerable by the IUCN (2002).

2. Borassus sambiranensis Jum. & H. Perrier

Morphology. Massive, solitary dioecious palm to 20m tall. Old leaf bases remain attached to the trunkuntil the palm reaches a certain height and thenthey fall away leaving distinctive scars on the stem.Stem is ventricose reaching 70 cm diameter at its


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12 (top left). Immature B. sambiranensis growing in an abandoned field to the north of Ambanja. 13 (top right). Aclose-up of the petioles of B. sambiranensis. The dark color and large petiole spines are characteristic. 14 (bottom left). Alarge female specimen of B. sambiranensis growing in the town of Hell-Ville on Nosy Bé. Though many inflorescenceswere present, no fruits or pyrenes were found. 15 (bottom right). Rolland standing on the wall of a Catholic mission tocollect Lodoicea maldivica. This male specimen is in full flower.

widest point. There are 14–22 green leaves in thecanopy and these are costapalmate with a radiusof up to 117 cm. The petiole is orange to yellowin color near the lamina and becomes dark brownnear the trunk. The petiole is 150–190 cm long,and 6–12 cm wide at the hastula. The petiolemargins are armed with large black erose spines.Each leaf has 100–110 leaflets and these are 8 cmwide with small brown scales on the surface. Themale inflorescence is up to 90 cm long andbranches to two orders. The tubular bracts areyellow and leathery with hard, acuminate apices.Inflorescence branches terminate in between 1and 3 rachillae which are dark brown, up to 35 cmlong and 3 cm diameter. Male rachillae are coveredin overlapping scales within which are pitscontaining the male flowers. Male flowers arearranged in a cincinnus with 8–10 flowers,emerging from the pit one at a time. Femaleinflorescences are unbranched and to 140 cm long.The number of empty bracts is unknown but thosecollected have woody acuminate apices. Theflower-bearing section of the inflorescence is upto 90 cm long with up to 30 flowers. Femaleflowers are large and solitary. Fresh mature fruitswere not seen so color is undetermined. They areup to 13 cm long and 11 cm diameter and contain1–3 pyrenes. The pyrenes are small, 6.8–8.4 cmlong and 6.1–7.1 cm broad.

Distribution. In Madagascar, restricted to theSambirano region in the north-west (Antsiranana& Northern Mahajanga provinces). Jumelle andPerrier de la Bâthie (1913) reported that the specieswas found between the Ifasy and Sambirano Riversand near the northern town of Ambilobe. Despiteintensive searching, only one specimen (ajuvenile) was found to the north of the SambiranoRiver (Figs. 12, 13). Jumelle & Perrier de la Bâthie(1945) noted that the species occurs on the islandof Nosy Mitsiou but this could not be verified.The specimens found on nearby Nosy Bé werecultivated. Also occurs in the Comoro archipelagoon Mayotte (Ludwig 1999).

Habitat. Riverine forest, including disturbed areas,at elevations of 0–50 m above sea level. Also foundon disused agricultural land.

Ecology. Due to the comparative rarity of thisspecies, very little is known of its ecology. As withthe previous species, it provides nesting sites forcolonies of Sakalava Weaver birds. Only two fertilemale specimens were observed in the wild and, aswith B. madagascariensis, honeybees were the onlyinsects visiting the flowers. No other animals wereobserved in the canopy. There are only four fruitsof B. sambiranensis in the herbarium collectionamassed for this study. They are consistentlysmaller than those of B. madagascariensis but may

still be too large for dispersal by any ofMadagascar’s native animals. It is possible that thefruits may be partially consumed while in thecanopy by bats or lemurs, though this would notprovide any dispersal. The only large ground-dwelling animal in Madagascar is the bush pig(Potamochoerus larvatus) which commonly occursin disturbed secondary forest and agricultural areas(Garbutt 1999), a habitat it shares with bothMalagasy species of Borassus. Perhaps this pig,which is known to consume fallen fruit, is adispersal agent for Borassus?

Conservation Status. During our fieldwork in theSambirano region, it was extremely difficult tolocate B. sambiranensis. Herbarium specimens havebeen collected from only six locations in thenorth-west of Madagascar. Beentje reports that hefound a population of 15 adult plants with someregeneration (in Dransfield & Beentje 1995).However during our recent trip, only a singlejuvenile and two male trees were found in thewild. Borassus sambiranensis is listed as endangeredby the IUCN (2002).

3. Borassus aethiopum Mart.

Morphology. Massive, solitary dioecious palm to 20m tall or more. Old leaf bases remain attached tothe trunk until the palm reaches maturity andthen they fall away leaving distinctive scars onthe stem. Stem is ventricose reaching 90 cmdiameter at its widest point. There are 18–27 greenleaves in the canopy and these are costapalmatewith a radius of up to 190 cm. The petiole is yellowin color near the hastula, and becomes darkertowards the trunk. Petiole is up to 220 cm long,and 4–9 cm wide at the hastula. The petiolemargins are armed with large black erose spines.Each leaf has 80–120 leaflets and these are 10 cmwide with small brown scales on the surface.Brown indumentum can be found on youngerleaves, particularly near the hastulae. The maleinflorescence is up to 150 cm long and branchesto two orders. The tubular bracts are yellow andleathery with some brown indumentum, and havehard, acuminate apices. Inflorescence branchesterminate in 1–3 rachillae which are dark brown,up to 50 cm long and 3 cm diameter. Malerachillae are covered in overlapping scales withinwhich are pits containing the male flowers. Maleflowers are arranged in a cincinnus with 8–14flowers, emerging from the pit one at a time.Female inflorescences are unbranched and to 160cm long. There are 7–9 empty bracts with brownindumentum and woody acuminate apices. Theflower-bearing section of the inflorescence is upto 96 cm long with 10–28 flowers. Female flowersare large and solitary. Fruits are orange to brownin color with a waxy surface. They are up to 15 cm


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long × 10 cm diameter with a sunken or depressedapex, and contain between one and three pyrenes.The pyrenes have a variable shape and are 6.9–10.9cm long and 5.8–10.5 cm broad.

Distribution. Sub-Saharan Africa. In the East,recorded from the Central African Republic,Democratic Republic of Congo, Kenya, Malawi,Mozambique, Rwanda, South Africa, Tanzania(including Pemba & Zanzibar), Uganda, Zambiaand Zimbabwe. Pascal & Labat (2002) report apopulation of B. aethiopum at Pointe Saziley onMayotte (Comoro Archipelago). This is probablythe Mayotte population of B. sambiranensisreported by Ludwig (1999).

Habitat. Patchy distribution, particularly alongriver valleys in gallery forest at elevations of0–1200 m above sea level. Locally abundant.

Ecology. Borassus aethiopum is widespread intropical Africa and dominates the plantcommunities in which it occurs. Several animalspecies exploit this palm and its relatives. As inMadagascar, weaverbirds attach their nests to thepalm leaf segments. In Kenya, only the VillageWeaver (Ploceus cucullatus) was observed utilizingB. aethiopum as a nest site, although other Kenyanweavers including the Spectacled Weaver (P.ocularis), Golden Palm Weaver (P. bojeri) andAfrican Golden Weaver (P. subaureus) frequentlynest in palms. Other Kenyan birds which selectBorassus as a nest site include the Red-neckedFalcon (Falco chiquera), African Palm Swift(Cypsiurus parvus) and Collared Palm Thrush(Cichladusa arquata).

While the pollination strategy of B. aethiopumremains unknown, there has been considerablespeculation as to the method of seed dispersal.Though there have been no documented studieswhich examined the subject thoroughly, severalobservations of animals feeding on the fruits havebeen made. These animals include elephants,baboons and three bat genera (Zona & Henderson1989). Dransfield (1986a) reported that lions mayeat the fruits of B. aethiopum while McGrew et al.(1988) speculated that chimpanzees may also eatthe fruit. It is unclear to what extent these animalsprovide effective seed dispersal. Burtt & Salisbury(1929) found germinating Borassus pyrenes in thedung of elephants in the Singida District ofTanzania. This remains the only record of effectiveanimal-mediated seed dispersal in this palm. Otherpossible methods of dispersal include water (B.aethiopum is common in riverine forest andfloodplains) and man.

Conservation Status. Borassus aethiopum is not listedby the IUCN although some populations aredeclining (Davies & Pritchard 1998). The three

populations of B. aethiopum examined in Kenya arelarge with regeneration occurring. However, noneof these populations is within a protected areaand effective seed dispersal may also be curtailed.While baboons are present at all three sites,elephants (probably the most effective animaldispersal agent) are absent. Elephants are presentwithin the Shimba Hills National Reserve but arecontained within the park by a fence and thushave no access to the large Borassus populationoutside.

Discussion

The fieldwork described here allowed newherbarium material of African Borassus to becollected, adding considerably to that alreadyavailable. It is hoped that in the near future aphenetic analysis of the morphology of thesespecimens will provide conclusive proof as to thetaxonomic status of Borassus in Madagascar andEast Africa. In addition a fieldtrip to Burkina Faso,currently in preparation, will allow herbariumspecimens of West African Borassus to be collectedand included in the analysis. However, it is nowpossible to present some preliminary conclusionsof the morphological study.

There are two taxonomic questions which must beconsidered. Firstly, can Borassus madagascariensisand B. sambiranensis be differentiated from eachother? Secondly, can either species bedistinguished from B. aethiopum in mainlandAfrica?

In The Palms of Madagascar, Dransfield & Beentje(1995) described three characters which could beused to distinguish B. madagascariensis from B.sambiranensis. Firstly, the pistillate rachilla of theformer species is shorter than that of the latter.However, newly collected material has shown thatB. madagascariensis can have a pistillate rachilla ofup to 90 cm long as in B. sambiranensis. It doesappear that B. sambiranensis has a greater numberof female flowers (ca. 30, compared with 7–20 inB. madagascariensis, Dransfield & Beentje 1995)though only two female rachillae of this specieshave been collected. The third character, fruit size,together with the correlated character of pyrenesize, also appears to distinguish the two Malagasyspecies from each other (see Table 1). Jumelle &Perrier de la Bâthie (1913) and Beccari (1914) bothnoted the large black spines on the petiole marginsof B. sambiranensis and these distinguish thatspecies from B. madagascariensis, which has verysmall petiole spines (Fig. 16).

While it appears that both Malagasy species ofBorassus can be distinguished from one other, itis also necessary to compare these species with B.aethiopum. Beccari (1914) suggested that B.


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sambiranensis was very similar to B. aethiopum var.bagamojensis (described from East Africa), while B.madagascariensis was said to resemble B. deleb.Borassus deleb, together with the varieties of B.aethiopum described by Beccari were later sunkinto that species by Dransfield (1986a). Dransfield& Beentje (1995) noted that there were fewcharacters which could be used to separate theMalagasy taxa from B. aethiopum, and cited agreater number of leaves in the canopy, a shortercosta, fewer empty bracts and fruit of ca. 12 cm ×14 cm in that species.

It is apparent from Table 1 that few charactersexist to distinguish B. sambiranensis from B.aethiopum. When encountered in the field, thetwo taxa are indistinguishable. Particularly strikingis the similarity in the petiole armature. Almostnone of the morphological differences enumeratedby Dransfield and Beentje (1995) was applicableas the measurements for B. sambiranensis fellwithin the range of variation exhibited by B.aethiopum in East Africa. The fruits of B.sambiranensis are very small, but such small fruitsexist in B. aethiopum, and this was confirmed usingthe morphological data collected from the femaletrees felled in Kenya. The only other slightdifference noted in the field was the orange-yellowcolor of the distal section of the petiole in B.sambiranensis, compared with the yellow-greencolor found in B. aethiopum. In the originaldescription of Jumelle and Perrier de la Bâthie(1913), the petiole is described as being golden.However, colors can be difficult to interpret asthey can vary with light intensity, and the colorhas been lost in most old herbarium specimens.The preliminary assessment is that B. sambiranensisshould be placed in synonymy with B. aethiopum.

Borassus madagascariensis, on the other hand,possesses several characters which distinguish it

from B. aethiopum. The petiole margins are armedwith small spines less than 1 cm long. These spinescan be erose, such as is found in B. aethiopum, orcan be serrated like a fine-toothed saw. The petioleitself is yellow-green in color along its entirelength. This feature is most noticeable near thestem where the green base of the petiole contrastswith the gray stem. In B. aethiopum, the petioletends to become darker in color towards the stem.For comparison, see Fiugres 4, 10 and 13.

The fruits of B. madagascariensis are the largest inthe genus and have a pointed apex. This contrastswith the slightly smaller, squat fruits of B.aethiopum which typically have a sunken ordepressed apex. There was some overlap in sizebetween the fruits of B. madagascariensis in theherbarium and those of B. aethiopum measured inthe field. This could be due to the fact that theherbarium specimens are dried and may haveshrunk during the process. However, it is possiblethat larger fruits of B. aethiopum exist. A pyrene wascollected in the Central African Republic (J. M.Fay s.n.) measuring 10.9 cm long by 10.5 cm wide.No other material was collected and so the identityof this species could not be verified but only B.aethiopum has been recorded in the CAR. The fruit,which would have contained between one andthree of these pyrenes, must have been very large.

The characters described above, and particularlythe petiole armature, can be used to recognizeBorassus madagascariensis both in the field and inthe herbarium. It could be that this species isderived from B. aethiopum, and indeed preliminaryresults from the molecular study show that thetwo species are sister taxa. However, it appears tobe distinctive enough to warrant continuedrecognition as a species.

The preliminary results published here awaitconfirmation using morphological and molecular


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16. Petiole sectionscollected fromAfrican Borassus.From left to right: B.sambiranensis(Bayton &Ranaivojaona 53), B.aethiopum (Bayton& Obunyali 14) andB. madagascariensis(Bayton &Ranaivojaona 46).

analyses. If they are confirmed, then nomen-clatural changes will follow.

Acknowledgments

RPB thanks his supervisors Dr. Barbara Pickersgill(Reading), Dr. John Dransfield and Dr. Bill Baker(RBG Kew) for their support and advice. RPBthanks the International Palm Society and theCentral Florida Palm Society for funding the tripto Madagascar, and the South Florida Palm Societyfor funding the trip to Kenya. In addition, RPBacknowledges the continued financial support ofthe Natural Environment Research Council(NERC). RPB and RR thank Hélène Ralimanana,Solofo Rakotoarisoa and Dr. Adam Britt (RBG Kew)for their help in Madagascar. RPB and CO thankDr. Henk Beentje, Dr. Aaron Davis, Dr. Kaj Vollesen(RBG Kew), Quentin Luke, Dr. Muthama Muasyaand Dr. Siro Masinde (EA) for their help in Kenya.Many thanks to the Myles family for taking careof RPB in Nairobi. We thank the herbaria thatsupplied us with specimens for this project: AAU,BH, BM, FTG, K and P. Many thanks to JustinMorat for constructing the maps. Last but notleast, many thanks to Sue Mott, Carole Raynor,Christine Bradshaw and Anne Davis in the Schoolof Plant Sciences at the University of Reading.

LITERATURE CITED

BAROT, S. AND J. GIGNOUX. 1999. Populationstructure and life cycle of Borassus aethiopumMart.: Evidence of early senescence in a palmtree. Biotropica 31: 439–448.

BECCARI, O. 1914. Studio sui Borassus e descrizionedi un genere nuovo asiatico di Borasseae. Webbia4: 293–385.

BEENTJE, H. 1994. Kenya trees, shrubs and lianas.National Museums of Kenya, Nairobi.

BOJER, W. 1837. Hortus Mauritianus: ouénumération des plantes, exotiques et indigènes,qui croissent a l’Ile Maurice, disposées d’aprés laméthode naturelle. 311.

BURTT, B.D. AND E.J. SALISBURY. 1929. A record offruits and seeds dispersed by mammals and birdsfrom the Singida District of Tanganyika Territory.Journal of Ecology 17: 351–355.

DAVIES, R.I. AND H.W. PRITCHARD. 1998. Seedconservation of dryland palms of Africa andMadagascar: Needs and prospects. Forest GeneticResources 26: 37–43.

DRANSFIELD, J. 1986a. Palmae. In R. M. POLHILL (ed.).Flora of Tropical East Africa. A.A.Balkema,Rotterdam.

DRANSFIELD J. 1986b. A guide to collecting palms.Annals of the Missouri Botanical Garden 73:166-176.

DRANSFIELD, J. AND H. BEENTJE. 1995. The Palms ofMadagascar. The Royal Botanic Gardens, Kewand the International Palm Society.

GARBUTT, N. 1999. Mammals of Madagascar. PicaPress, East Sussex.

GERLACH, J. 2003. Pollination in the coco-de-merLodoicea maldivica. Palms 47: 135–138.

HENDERSON, A. 1986. A review of pollination studiesin the Palmae. The Botanical Review 52:221–259.

HEPPER, F.N. 1976. The West African herbaria ofIsert and Thonning. Bentham-Moxon Trust andthe Royal Botanic Gardens, Kew.

IUCN. 2002. 2002 IUCN red list of threatenedspecies. Online at www.redlist.org.

JUMELLE, H. AND H. PERRIER DE LA BÂTHIE. 1907. Laflore du Nord-Ouest de Madagascar. Ann. Inst.Bot.-Géol. Colon. Marseille, II, 5: 372–389.

JUMELLE, H. AND H. PERRIER DE LA BÂTHIE. 1913.Palmiers de Madagascar. Ann. Inst. Bot.-Géol.Colon. Marseille, III, 1(1): 61–68.

JUMELLE, H. AND H. PERRIER DE LA BÂTHIE. 1945.Palmiers. In H. HUMBERT (ed.). Flore deMadagascar et des Comores 30e famille.Imprimerie officielle, Antananarivo.

LUDWIG, N. 1999. Notes on the palms of Mayotte,Comoro Islands, Indian Ocean. Palms 43:149–151.

MARTIUS, C.P.F. VON. 1838. Historia NaturalisPalmarum 3: 219–222. Munich.

MCGREW, W.C., P.J. BALDWIN AND C.E.G. TUTIN.1988. Diet of wild chimpanzees (Pan troglodytesverus) at Mt. Assirik, Senegal: 1. Composition.American Journal of Primatology 16: 213–226.

PASCAL, O. AND J.N. LABAT. 2002. Plantes et Fôretsde Mayotte. Muséum National d’HistoireNaturelle, Paris.

RATSIRARSON, J. AND J.A. SILANDER. 1996.Reproductive biology of the threatenedMadagascar Triangle Palm: Neodypsis decaryiJumelle. Biotropica 28: 737-745.

SAVAGE, A.J.P. AND P.S. ASHTON. 1983. The populationstructure of the double coconut and some otherSeychelles palms. Biotropica 15: 15–25.

WARBURG, O. 1895. In H. G. A. ENGLER (ed.).Pflanzenw. Ost-Afrikas, B: 20.

ZONA, S. AND A. HENDERSON. 1989. A review ofanimal-mediated seed dispersal of palms.Selbyana 11: 6–21.


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