Amaranthus Interruptus R. Dr. on Jarvis Island in the Central Pacific!

Amaranthus interruptus R. Dr. on Jarvis Island in the Central Pacific!

UNO H. ELIASSON 2

ABSTRACT: 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.

IN MAY 1982 Professor Harold St. John at the tered over a patch 100ft. square.... The only B. P. Bishop Museum in Honolulu handed place this specimen has been seen, and it is, over to me two unidentified plant specimens without doubt, rare .... June 5, 1935.... Ahia collected in June 1935 on Jarvis Island in the and Graf." Thanks to the courtesy of Profes Central Pacific. The plants proved to be con sor F. R. Fosberg at the Smithsonian Insti specific with Amaranthus interruptus R. tution in Washington, it was possible to trace Brown, a principally North Australian species. and study a considerably more recent collec Jarvis is an island ofEast Central Polynesia tion of the same species from Jarvis taken by locatedjustsouth ofthe equatorin the Central C. D . Hackman in March 1964 during the Pacific. It is a low island of coral origin; the U.S. Pacific Ocean Biological Survey Pro highest part does not exceed 5 m above mean gram. According to the information on the tide. It has a central depression with remains label, the "small herb, light green in color, was of a saltwater lagoon, but there is no open collected in the central island depression, 5 water body in the interior (Christophersen 12in., restricted to an area about 300 x 500 ft. 1927). As is to be expected on a low atoll, the sq." flora is poor. Only eight vascular plants were Although differing in lower growth, smaller recorded by Chri stophersen (1927). He de leaves, more compact inflorescences, and scribed the vegetation of the central depres smaller seeds, the Jarvis specimens agree in sion as very open and scattered; only in a most characteristics with North Australian few places did Sesuvium portulacastrum L. and material, including type material, of Amaran Boerhaavia tetrandra Forster form dense car thus interruptus. The average longest diameter pets. On the beach crests and their slopes the of the seed is 0.76mm (s = 0.063, n = 10) vegetation formed a continuous cover com in the Jarvis specimens as compared with prising Lepturus repens (Forster) R. Brown , 0.99 mm (s = 0.088, n = 10) in the Australian Boerhaavia tetrandra, Portulaca lutea Solan plants; but apart from the difference in seed der, and Sidafallax Walpers. Christophersen's size, there is good agreement in floral charac enumeration seems to be the only plant list teristics . The Jarvis plants are too close to A. published from the island. interruptus to be regarded as a separate taxon. The two Amaranthus collections from 1935 The differences mentioned may well be modi were made by Ahia and Grafand by Judd and fications. Mitchell, respectively. An annotation label ac The occurrence of A. interruptus on Jarvis companying the Ahia and Graf specimen in the Central Pacific is noteworthy. Although reads: " Collected 100yd. south ofcamp from the species has been recorded from Papuasia, a slightly raised spot. Plant (about 200) scat- permanent occurrence outside Australia has been doubted (Kanis 1972). Collections from southeastern New Guinea, the Bismarck Ar 1 Manuscript accepted September 1985. chipelago, and the Solomon Islands have been 2 Dept. of Systematic Botany, University of Gothen berg, Carl Skottsbergs Gata 22, S-413 19, Gothenberg, interpreted as resulting from temporary intro Sweden. ductions from Australia (Kanis 1972, 1974). 106 Amaranthus on Jarvis Island-s-Et.txssox 107

Certainly A. interruptus is not indigenous on have been recorded on the Hawaiian Islands Jarvis. No species of Amaranthus was noted (St. John 1973), but, on the whole, the genus is by the Whippoorwill Expedition to the island poorly represented in the Pacific. One endemic in 1924 (Christophersen 1927). Moreover, species, A. brownii Christoph. & Caum, is some decades ago Jarvis was exploited for known from Nihoa, one of the Leeward guano, and there may have been ample oppor Islands in the Hawaiian chain (Christophersen tunities for diaspores to be brought to the and Caum 1931). In the Galapagos Islands island. In all likelihood, A. interruptus reached there are three endemic species, but this archi Jarvis some time between 1924 and 1935. It is pelago is more closely connected to South remarkable, however, that it became so well America than to the Pacific as regards floristic established on the island that it was still there relationships. No endemic species or species some 30 years after the first collection. Unfor with restricted distribution are to be expected tunately I know of no more recent collections on low coral islands in the Pacific. The scat or observations of the plant. It may well still tered records ofAmaranthus from such locali be there. It is inconspicuous and may at first ties (A . dubius Mart., A spinosus L., A . viridis sight be mistaken for Chenopodium am L.; Fosberg, pers. comm.) represent intro brosioides L. duced weeds. The Jarvis plant is a monoecious species, As A . interruptus on Jarvis Island differs in characterized by five tepals , three to five sta some respects from Australian specimens, a mens, and indehiscent utricles which are description is given here based on the speci strongly wrinkled in the lower half and mens cited from Jarvis. See Figures 1 and 2. smooth and composed of a spongy tissue in Monoecious, probably annual plant, to the upper part. The plant would key to A. 20em tall. Taproot vertical, slender, gradually crispus (Lesp. & Thev.) A. Br. or A. muricatus tapering. Stem richly branched from base, (Moq.) Gillies in Standley's (1917) treatment glabrous, striate and sulcate. Leaves petiolate, of the North American species. Amaranthus blade ovate-oblong to lanceolate, obtusely crispus differs in having crispate leaves, apiculate at apex, narrowed and gradually spathulate pistillate tepals, consistently five tapering along petiole at base, glabrous, stamens, a morphologically different fruit, somewhat undulate, mostly 5-10 (-15) mm and the uppermost flower clusters not spici long and 3-5 mm wide, petiole to ca. 5 mm formly arranged. Amaranthus muricatus is long but not sharply set off from blade. In larger in all parts, the utricle is rugose florescences appearing spiciform, interrupted tuberculate all over its surface, and the seed is below, comprising cymes densely arranged in larger, about 1.5mm in diameter. In Covas rounded axillary glomerules 5-7 mm wide, (1941) the Jarvis plant would key to the vicin sometimes almost completely obscuring stems ity ofA . crispus, A. standleyanus Parodi, or A. and leaves. Flower-subtending bracts shorter vulgatissimus Speg. The two last-mentioned than perianth, ovate to ovate-triangular, con species differ from the Jarvis specimens, cave, ca. 1mm long, transparent except near among other things, in differently shaped pis green midnerve. Tepals of male flowers 5, tillate tepals and different utricles. elliptic to oblanceolate, scarious, midnerve Amaranthus interruptus normally has inde greenish, longest tepals ca. 2 mm long, inner hiscent utricles. If the fruits were considered tepals shorter; stamens 3-5, anthers ca. 1mm to be circumscissile, the Jarvis plant would key long or shorter. Tepals of female flowers 5, in many works to A . blitoides S. Watson. oblong-obovate or oblong-spathulate, short Apart from differences in the indehiscent acuminate at apex, scarious, the green mid fruits , the Jarvis plant differs from A. blitoides nerve conspicuous and branched, especially in in the rugose utricles with the structurally dif the outer tepals , tepals ca. 1.5 mm long, the ferent upper part, the short bracts, the smaller innermost only slightly shorter than the outer seeds, and the tendency ofthe upper cymes to ones; utricle indehiscent, in mature flowers ca. form a spiciform inflorescence. 1.5 mm long, the lower seed-containing half Several introduced species of Amaranthus strongly rugose and wrinkled, the upper half 108 PACIFIC SCIENCE, Volume 40,1986

FIGURE 1. Amaranthus interruptus from Jarvis Island. A, Hackman 2 (HAW). B, Ahia & GrafP9(X) (BISH). Amaranthus on Jarvis Island-c-Et.rxssox 109

E E E

FIGURE 2. Amaranthus interruptus from Jarvis Island (Ahia & GrafP9(X)). A, E, male flowers. B, tepals from male flower. C, F, androecia with four and three stamens, respectively. D, bract from male flower, in the right figure seen from 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, utricles. L , seed seen from different sides. M, N, leaves. 110 PACIFIC SCIENCE, Volume 40,1986 smoother, composed of a spongy tissue; CHRISTOPHERSEN, E., and E. L. CAUM. 1931. stigma branches 3; seed ca. 0.75 mm in longest Vascular plants of the Leeward Islands, diameter, ca. 0.5 mm thick, reddish black, Hawaii. B. P. Bishop Mus. Bull. 81: 1-41. testa shiny, almost smooth. COVAS, G. 1941. Las Amarantaceas bon arienses.Darwiniana 5:328-368. SPECIMENS EXAMINED: Jarvis Island. 5 June KANIS, A. 1972. A review of the Amaran 1935, Ahia & Graf P9(X) (BISH). June 1935, thaceae in Papuasia. Contrib. Herb. Aus. Judd & Mitchell 51 (BISH) . 17 March 1964, 1:1-18. Hackman 2 (HAw). ---. 1974. Further notes on the Amaran thaceae in Papuasia. Contrib. Herb. Aus . 7:7-13. STANDLEY , P. C. 1917. Amaranthaceae. North LITERATURE CITED American Flora 21(2) :95-169. ST. JOHN, H. 1973. List and summary of the CHRISTOPHERSEN, E. 1927. Vegetation of Pa flowering plants in the Hawaiian Islands. cific equatorial islands. B. P. Bishop Mus. Pacific Tropical Botanical Garden Memoir Bull. 44: 1-79. No.1. Lawai , Hawaii.