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Benthic Marine Algae of Rotuma Island 429
Arnansia probably does not extend into the Pacific (R.E. Norris, pers. comm.), and hence a
re-examination of all reports of this genus in the region is called for.
Bostrychia Montagne 1842b: 39
Bostrychia tenella (Lamouroux) J . Agardh 1863 (1851-1863): 869; Okamura 1907: 96,
pl. 22, figs 1-13; Weber-van Bosse 1923: 363; Taylor 1960: 599; Durairatnam 1961: 69;
Chapman 1963: 130, fig. 135a, b; Womersley and Bailey 1970: 335; Dawes 1974: 154;
Jaasund 1976: 127, fig. 258; Woelkerling 1976: 116, fig. 133; Tsuda and Wray 1977: 104;
Cribb 1983: 106, pl. 66, figs 3, 4; Lewis 1984: 42; Tseng et al. 1984: 144, pl. 75, fig. 3;
Lewis and Nonis 1987: 22; Silva et al. 1987: 62; King and Puttock 1989: 34; Littler et al.
1989: 174; Tsuda 1991: 48; Coppejans and Prud'homme van Reine 1992a: 189.
Fucus tenellus Vahl 1802: 45 (type locality: St. Croix, Virgin Island).
Plocamium tenellum Lamouroux 18 13: 138 (nomen novum).
(Figs 129, 186)
Plants 5-20 mm high, found as rather soft, dense mosslike clumps; 3 times pinnately
branched with dense bilateral branching near the typically incurved tips. Aggregates almost
black, individual plants dark red to purple, main axis corticated 105-170 bm in diameter,
with 6-8 pericentral cells. Secondary branchlets 35-60 bm in diameter, at 170-200 p,m
intervals along main axis; polysiphonous, corticated below and uncorticated above. Ultimate
branchlets monosiphonous 12-24 p,m in diameter 10-20 cells long with individual cells
8-10 pm long.
Distribution
Fiji, Micronesia, New Caledonia, Solomon Islands, northern Australia, Indonesia, China,
Florida, Caribbean, Brazil, Tanzania.
Fijian Records
Kapraun and Bowden 1978: 201; South and Kasahara 1992: 65; Raj 1993: 49, fig. 14; In
Herb Bishop Museum, Hawaii (BISH 458108,4581 13).
Rotuman Distribution
Paptea (PI/ USP 444, *P3/ USP S5: 19).
Habitat and Remarks
Found as dense, almost black clumps at the bases of stilt-like roots of mangrove trees
(Bruguiera gymnorhiza) growing in an inland marine swamp about 300 m inland, intermixed
with coconut groves. No other algae were found in this habitat, hence it represented an
isolated population. This species was subsequently found growing on rocks, tree roots and
other objects close to the low tide mark on most Rotuman shores.
As Fucus tenellus Vahl, the intended basionym for Bostrychia tenella, is a later homonym
of F. tenellus Esper (1800: 197, pl. CIX) it is not given priority (see Silva et al. 1987: 62).
Plocamium tenellum Lamouroux is treated as a nomen novum in accordance with Article 72,
Note 1, of the ICBN.
Chondria C. Agardh 18 17: xviii
Key to the Rotuman Species of Chondria
1. Thallus creeping .................................................... C. simpliciuscula
1: Thallus erect ................................................................... .2
2. Plants dark red, up to 30 mm high, main axis to 1.5 mm in diameter ............ C. dasyphylla
2: Plants reddish-purple, up to 40 mm high; main axis 400-500 pm in diameter ....... C. sedifolia