19861 RAUWERDINK:METROXYLON Principes,30(4), 1986, pp. 165-180 An Essay on Metroxylon, the Sago Palm JeNB. ReuwnRomx Department of Plant Taxonomy, Agricultural Uniaersity, Wageningen, the Netherlands P.O. Box 8010, 6700 ED Wageningen Metroxylon is a genus of arborescent under cultivation. The aim of my survey palms of Papuasia and several island and the present paper has been to report groups of Micronesia and Melanesia. There on the variability of M. sagu in PNG, in are five species occurring in five separate the context of the diversity found in the areas. The most widespread taxon, M. genus as a whole. This paper may con- scLgu, covers Malaysia, Indonesia, Min- tribute towards an eventual monograph of danao, and New Guinea. The other four Metroxylon. taxa are endemic to the aforementioned island groups. Historyof the Genus The palms accumulate starch in the pith of their trunks and are a traditional source The first and most competentpublica- of carbohydrate. The best known r-epre- tion on sagopalms is by Rumphius(1741). sentative of the genus in this respect is In the Herbarium Amboinensehe gives M. sagu, known as the sago palm. This a meticulousdescription of the sagopalm species occupies the largest area. esti- as it occurs in Ambon. and he Dresents mated to cover 4 million ha in natural the taxonomic views of the inhabiiants on stands and about .2 million ha under cul- this palm. Four Ambonesespecies are tivation. With the exception of M. salo- described under the seneric name of monense.the other tp".i"t of Melroxylon Sagris.This namewas adopted by Caert- are not exploited for their starch content. ner (1788), but unfortunately alsoincluded At present, interest on Metroxylon as a Rctphia P. de Beauvois.Giseke (1792) starch-producing crop is focused on M. does not include Raphia and gives the sogu which grows in swampy areas usu- earliest binomial applying solely to the ally unsuitable for plantations of other descriptionof Rumphius'sS. genuina. The crops. So far, two international symposia name Sagus is, however, antedated by have been held to evaluate the exoloita- Metroxylon Rottboell(1783), basedpartly rion of sago starch (Sago I 977. Sago on Rumphius'sdescription, but in larger l9B0). In addition, an FAO expert con- part on specimensprovided for Rottboell sultation took place in Jakarta in 1984. by Dr. Koenig. The next author to adopt Studies were carried out in Indonesia Metroxylon was Von Martius (1845). (Team Proyek I9B2) and Papua New Nearly eighty years after Rottboell, Guinea (DME 1980, 1982). Wendland (1862) proposedthe generic The present author has made a taxo- name Coelococcusin which he described nomic survey for the Papua New Guinean a sagopalm from the Fiji Islands.Coelo- government in the Sepik River flood plain coccushas henceforwardbeen adopted by (Fig. l). An estimated one million ha of various other authors (Dingler lBB7, natural sago palm stands occur in PNG, Warburg 1896, Heim 1904) to classify and an additional 20 thousand ha are several species of sago palm from r66 PRINCIPES [Vor. 30 1 5 I I i l i ----f -Q*qo"orn- to -4or/ A\ rury 5 I r lt I / .63- ,1 /--.1 \. $ t\^/ '., \ a "\(_- ) +l 4\ , r... \ rf-t: Jtl \: ,F .,/f .r_ lr'--l 'c 't/' \ w}- v, .K \ =a:/I . Q; 1 1 't5 135 140 I.PapuaNewGuineawithanenlargedinsetshowingwheretheauthormadehiscollections' Micronesian and Melanesian islands; DiagnosticCharacters Metroxylon is used exclusively for those sago palms occurring throughout New A brief treatment of the diagnostic Guinea, Indonesia, and Malaysia. Beccari characters wrthin Metroxylon is appto- (1918) included Coelococcusin Metrox- priate. Especiallywhere the inflorescence ylon as a section,an opinion that has since is concerned,the application of correct teen followed. Somecommotion may have terminology to refer to particular units is arisen in the early sixties when Moore vital. In this paragraph,diagnostic char- l96D disclosedthat Rottboell'sMetrox- acters are treated in an order reflecting ylon is actually antedatedby SagrzsSteck the comparativeimportance of each char- (1757). However, Steck's publication is acter within the taxonomy of the genus: not effectively published, and Metroxylon the most significant character is treated tt conserved (t968) against this first. *".,T3. Inflorescence: The inflorescenceof r eB6l RAUWERDINK:METROXYLON t67 'rq@i. l:$i: C Q&' &r &s I s{, 2, g rF. ;: fs*- -t .*l l r F. I l. rth e I - -r t * *l\ t -r&a t 4 5 2. Fruits of Metroxylon sagu. 3. Spines on leaf sheathsand petioles of a mature specimen. 4. Fruits of M. amicarum. 5. M. sagu, somaticchromosomes in equatorialplane (photo by J. C. Arends). Metroxylon is extensively discussed in gle basal ovule in each locule, usually only Tomlinson (I971). For reasons of brevity a single seed matures in each fruit. This of this paper, reference to this publication seed contains a considerable amount of is made for interested readers. As far as hard, bony, homogenous endosperm which diagnostic characters are concerned, the has a very characteristic horseshoe shape shape of specific units of the inflorescence in vertical section, with a large chalazal has oroved useful. Most characteristic is cavity. The embryo is situated in a smaller, *hether branches of a certain order are second peripheral cavity. Differences pendulous or not. This single character between the taxa are found in the number enables unambiguous distinction of three of longitudinal series of scales on the fruit. out of the five species recognized in The divisionol lhe genusinto two sections Metroxylon. is based upon the number of scales. At the Fruits (Figs. 2,4): The fruits of specific level, the shape and the size of Metroxylon are covered with longitudinal the mature fruit is also diagnostic. series of imbricate rhomboidal scales (Fig. Spines (Fig. 3): Spinescence has been 4). The apex of the fruit is always emphasized in Metroxylon as an impor- mucronate, the mucro representing the tant diagnostic character throughout. remains of the style. Although the pistil Authors, such as Rumphius (1741) and of Metroxyktn is three-locular with a sin- Beccari (1918), as well as sago-subsisting r68 PRINCIPES lVoL. 30 people, all greatly value spinescencein length of spines may be governed by a iheir respectivetaxonomies. Among other comparatively simple genetic mechanism. thines this led to the division of the section Thus, different formae in the section Meioxylon into 17 taxa bY Beccari. Metroxylon (e.g. spiny vs. smooth) are However, in the section Coelococcushe considered to be only slightly different distinguished 7 taxa only. Probably this genotypesof a single species,M. sagu, was becauseBeccari lacked the extensive instead of two or more different speciesor collectionsand experiencein the field with subspecies.This assumptionwill be dealt these taxa that he had in Metroxylon' with in the Discussion. Like Beccari, the present author is famil- Srimatic Chromosome Numbers: iar with the section Metroxylon, but has Somatic chromosomenumbers of M' sagu scant knowledge of Coelococcus aparl were determined from root tiPS of and descrip- from herbarium specimens I) Seedlingsgrown at the Departmentof the data, all taxa in tions. According to Plant Taxonomy at Wageningen. The are spinescent, the section Coelococcus seedswere collected in the Sepik area but details such as length and abundance (PNG)by Mr. Van Kraalingenand all Such charac- of spinesare not available. specimenswere spiny. One seedlinghas betweentaxa ters enableme to distinguish beenpreserved at WAG (Rauwerdink in the section Metroxylon, and they may lsB). the section Coe- be of the same value in 2) Plants grown at the Department o{ in transverse lococcus.Spines are found TropicalCrop Scienceat Wageningen, the abaxialside crescent-shapedseries on from seeds obtained from the Singa- surface of the of a leaf, over the entire pore Botanical Gardens. Spiny as well of about 3 leaf sheath, and along a strip as unarmed plants were available. cm wide on the petiole and rachis. Spines are pectinate, flattened, of a brownish Permanentsquash preparations were made color, and confluent by their bases,i.e. accordins to the methods describedin De arrangedas in a comb(Figs. 12,13). Their Wilde and Arends (1979). The slides are length rangesfrom a few cm tp Io 22 crn. retained in the slide collection of the Furthermore, they are unequal' the mid- Department of Plant Taxonomy. No living dle one of a series usually being the lon- maierial from the other taxa in Metrox- gest. Reduction in length of spinesoccurs' ylon was available for an investigation. in which casethey are referred to as spi- The Singapore plants had already been nules. Spinulesare short, up to l0 mm investigatedby Verhaar (1977) ar 2n: long, and usually of a triangular form. The 26.The presentauthor also obtainedthe ultimate reductions of spinesare knoblike somaticchromosome number of 2n: 26 structures which occur exclusively on the in M. sagu (Fig. 5), both in the PNG baseof leaf sheaths.The variability in spine specimensand in the Singapore material. morphology in the section Metroxylon is The basicchromosome number of M. sagu : threefold. The first is related to the age can therefore be put at x 13, which of the palm. Crown leaves of a mature actualJymarks M. sogu as an exception specimen usually have spines that are in Calamoidpalms. The basic chromosome : much shorter than those on leaves from numberin thesepalms is x 14, accord- offshootsof the samepalm' Secondly,the ins- to Moore and Uhl (1982)' exact location of the spines is important. Analysis of Pollen: Recentanalyses on Especially in a mature palm, the spines the pollenmorphology of Metroxylon were on the leaf sheath are longer than the undertaken by Sowumni (1972) and spines on the petiole and rachis. In the Thanikaimoni(1970). This paragraph third place, I am of the opinion that the presents a few observationsby the latter r9861 RAUWERDINK:METROXYLON r69 I B t ; ll t-' u )t E a il L< I DT a, saga, overview, bar : 1.0 6-7.