Amaranthus interruptus R. Br.,' a principally Australian species,
has been recorded on Jarvis Island in the Central Pacific. The plant is supposed
to have been introduced to the island some time between 1924 and 1935. It
evidently became well established and was still there in 1964

Eliasson, Uno H.

Pacific Science

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Pacific Science (1986), vol. 40, nos. 1-4© 1987 by the University of Hawaii Press. All rights reservedAmaranthus interruptus R. Dr. on Jarvis Island in the Central Pacific!UNO H . ELIASSON2ABSTRACT: Amaranthus interruptus R. Br.,' a principally Australian species,has been recorded on Jarvis Island in the Central Pacific. The plant is supposedto have been introduced to the island some time between 1924 and 1935. Itevidently became well established and was still there in 1964.tered over a patch 100ft. square.... The onlyplace this specimen has been seen, and it is,without doubt, rare .... June 5, 1935.... Ahiaand Graf." Thanks to the courtesy of Profes-sor F. R. Fosberg at the Smithsonian Insti-tution in Washington, it was possible to traceand study a considerably more recent collec-tion of the same species from Jarvis taken byC. D . Hackman in March 1964 during theU.S. Pacific Ocean Biological Survey Pro-gram. According to the information on thelabel , the "small herb, light green in color, wascollected in the central island depression, 5-12 in., restricted to an area about 300 x 500 ft.sq."Although differing in lower growth, smallerleaves, more compact inflorescences, andsmaller seeds, the Jarvis specimens agree inmost characteristics with North Australianmaterial, including type material, of Amaran-thus interruptus. The average longest diameterof the seed is 0.76mm (s = 0.063, n = 10)in the Jarvis specimens as compared with0.99 mm (s = 0.088, n = 10) in the Australianplants; but apart from the difference in seedsize, there is good agreement in floral charac-teristics . The Jarvis plants are too close to A.interruptus to be regarded as a separate taxon.The differences mentioned may well be modi-fications.The occurrence of A. interruptus on Jarvisin the Central Pacific is noteworthy. Althoughthe species has been recorded from Papuasia,permanent occurrence outside Australia hasbeen doubted (Kanis 1972). Collections fromsoutheastern New Guinea, the Bismarck Ar-chipelago, and the Solomon Islands have beeninterpreted as resulting from temporary intro-ductions from Australia (Kanis 1972, 1974).106IN MAY 1982 Professor Harold St. John at theB. P. Bishop Museum in Honolulu handedover to me two unidentified plant specimenscollected in June 1935 on Jarvis Island in theCentral Pacific. The plants proved to be con-specific with Amaranthus interruptus R.Brown, a principally North Australian species.Jarvis is an island of East Central Polynesialocated just south of the equator in the CentralPacific. It is a low island of coral origin; thehighest part does not exceed 5 m above meantide. It has a central depression with remainsof a saltwater lagoon, but there is no open-water body in the interior (Christophersen1927). As is to be expected on a low atoll, theflora is poor. Only eight vascular plants wererecorded by Chri stophersen (1927). He de-scribed the vegetation of the central depres-sion as very open and scattered; only in afew places did Sesuvium portulacastrum L. andBoerhaavia tetrandra Forster form dense car-pets . On the beach crests and their slopes thevegetation formed a continuous cover com-prising Lepturus repens (Forster) R. Brown ,Boerhaavia tetrandra, Portulaca lutea Solan-der, and Sidafallax Walpers. Christophersen'senumeration seems to be the only plant listpublished from the island.The two Amaranthus collections from 1935were made by Ahia and Grafand by Judd andMitchell, respectively. An annotation label ac-companying the Ahia and Graf specimenreads: " Collected 100yd. south of camp froma slightly raised spot. Plant (about 200) scat-1 Manuscript accepted September 1985.2 Dep t. of Systematic Botany, University of Gothen-berg, Carl Skottsbergs Gata 22, S-413 19, Gothenberg,Sweden.Amaranthus on Jarvis Island-s-Et.txssoxCertainly A. interruptus is not indigenous onJarvis. No species of Amaranthus was notedby the Whippoorwill Expedition to the islandin 1924 (Christophersen 1927). Moreover,some decades ago Jarvis was exploited forguano, and there may have been ample oppor-tunities for diaspores to be brought to theisland. In all likelihood, A. interruptus reachedJarvis some time between 1924 and 1935. It isremarkable, however, that it became so wellestablished on the island that it was still theresome 30 years after the first collection. Unfor-tunately I know of no more recent collectionsor observations of the plant. It may well stillbe there. It is inconspicuous and may at firstsight be mistaken for Chenopodium am-brosioides L.The Jarvis plant is a monoecious species,characterized by five tepals , three to five sta-mens, and indehiscent utricles which arestrongly wrinkled in the lower half andsmooth and composed of a spongy tissue inthe upper part. The plant would key to A.crispus (Lesp . & Thev.) A. Br. or A. muricatus(Moq.) Gillies in Standley's (1917) treatmentof the North American species. Amaranthuscrispus differs in having crispate leaves,spathulate pistillate tepals, consistently fivestamens, a morphologically different fruit,and the uppermost flower clusters not spici-formly arranged. Amaranthus muricatus islarger in all parts, the utricle is rugose-tuberculate all over its surface, and the seed islarger, about 1.5mm in diameter. In Covas(1941) the Jarvis plant would key to the vicin-ity of A . crispus, A. standleyanus Parodi, or A.vulgatissimus Speg. The two last-mentionedspecies differ from the Jarvis specimens,among other things, in differently shaped pis-tillate tepals and different utricles.Amaranthus interruptus normally has inde-hiscent utricles. If the fruits were consideredto be circumscissile, the Jarvis plant would keyin many works to A . blitoides S. Watson.Apart from differences in the indehiscentfruits , the Jarvis plant differs from A. blitoidesin the rugose utricles with the structurally dif-ferent upper part, the short bracts, the smallerseeds, and the tendency of the upper cymes toform a spiciform inflorescence.Several introduced species of Amaranthus107have been recorded on the Hawaiian Islands(St. John 1973), but, on the whole, the genus ispoorly represented in the Pacific. One endemicspecies, A. brownii Christoph. & Caum, isknown from Nihoa, one of the LeewardIslands in the Hawaiian chain (Christophersenand Caum 1931). In the Galapagos Islandsthere are three endemic species, but this archi-pelago is more closely connected to SouthAmerica than to the Pacific as regards floristicrelationships. No endemic species or specieswith restricted distribution are to be expectedon low coral islands in the Pacific. The scat-tered records of Amaranthus from such locali-ties (A . dubius Mart., A spinosus L., A . viridisL.; Fosberg, pers. comm.) represent intro-duced weeds.As A . interruptus on Jarvis Island differs insome respects from Australian specimens, adescription is given here based on the speci-mens cited from Jarvis. See Figures 1 and 2.Monoecious, probably annual plant, to20 em tall. Taproot vertical, slender, graduallytapering. Stem richly branched from base ,glabrous, striate and sulcate. Leaves petiolate,blade ovate-oblong to lanceolate, obtuselyapiculate at apex, narrowed and graduallytapering along petiole at base , glabrous,somewhat undulate, mostly 5-10 (-15) mmlong and 3-5 mm wide, petiole to ca. 5 mmlong but not sharply set off from blade. In-florescences appearing spiciform, interruptedbelow, comprising cymes densely arranged inrounded axillary glomerules 5-7 mm wide,sometimes almost completely obscuring stemsand leaves. Flower-subtending bracts shorterthan perianth, ovate to ovate-triangular, con-cave, ca. 1mm long, transparent except neargreen midnerve. Tepals of male flowers 5,elliptic to oblanceolate, scarious , midnervegreenish, longest tepals ca. 2 mm long, innertepals shorter; stamens 3-5, anthers ca. 1mmlong or shorter. Tepals of female flowers 5,oblong-obovate or oblong-spathulate, short-acuminate at apex, scarious, the green mid-nerve conspicuous and branched, especially inthe outer tepals , tepals ca. 1.5 mm long , theinnermost only slightly shorter than the outerones; utricle indehiscent, in mature flowers ca.1.5 mm long , the lower seed-containing halfstrongly rugose and wrinkled, the upper half108 PACIFIC SCIENCE, Volume 40,1986FIGURE 1. Amaranthus interruptus from Jarvis Island. A, Hackman 2 (HAW). B, Ahia & GrafP9(X) (BISH).Amaranthus on Jarvis Island-c-Et.rxssox 109wcEEMElFIGURE 2. Amaranthus interruptus from Jarvis Island (Ahia & GrafP9(X) ) . A , E, male flowers. B, tepals from maleflower. C, F, androecia with four and three stamens, respectively. D, bract from male flower, in the right figure seenfrom adaxial side. G, female flower. H, tepa ls from female flower seen from adax ial (uppe r row) and lateral (lower row)sides. J , K, ut ricles. L , seed seen from different sides. M, N, leaves.110smoother, composed of a spongy tissue;stigma branches 3; seed ca . 0.75 mm in longestdiameter, ca. 0.5 mm thick, reddish black,testa shiny, almost smooth.SPECIMENS EXAMINED: Jarvis Island. 5 June1935, Ahia & Graf P9(X) (BISH). June 1935,Judd & Mitchell 51 (BISH). 17 March 1964,Hackman 2 (HAw).LITERATURE CITEDCHRISTOPHERSEN, E. 1927. Vegetation of Pa-cific equatorial islands. B. P. Bishop Mus.Bull. 44: 1-79.PACIFIC SCIENCE, Volume 40,1986CHRISTOPHERSEN, E., and E. L. CAUM. 1931.Vascu lar plants of the Leeward Islands,Hawaii . B. P. Bishop Mus. Bull. 81: 1-41.COVAS, G. 1941. Las Amarantaceas bon-arienses. Darwiniana 5 :328-368.KANIS, A. 1972. A review of the Amaran-thaceae in Papuasia. Contrib . Herb. Aus.1:1-18.---. 1974. Further notes on the Amaran-thaceae in Papuasia. Contrib. Herb. Aus .7:7-13.STANDLEY, P. C. 1917. Amaranthaceae. NorthAmerican Flora 21(2) :95-169.ST. JOHN, H . 1973. List and summary of theflowering plants in the Hawaiian Islands.Pacific Tropical Botanical Garden MemoirNo.1. Lawai , Hawaii .

Amaranthus interruptus R. Br. on Jarvis Island in the Central Pacific

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Amaranthus interruptus R. Br. on Jarvis Island in the Central Pacific

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