Tripoma arboreum Hirohito, 1995

Colonies erect, branched, the tallest 75 mm high.

Hydrorhiza reptant on stem of host, tubular, undulating, sometimes contorted.

Erect stems arising from hydrorhiza, some hydrothecae arising directly from stolon. Most stems polysiphonic, several younger stems monosiphonic and unbranched, older stems with increasingly polysiphonic. Stem internodes variable in length, cylindrical, smooth, nodes usually distinct, transverse to slightly oblique, marked by a constriction in perisarc. Apophyses alternate, long, distal on internode, directed upwards at c. 45° to internodal axis, often shifted slightly around stem, distal node of apophysis transverse, sometimes extended into two or three segments, each with deep transverse node.

Hydrothecae inverted conical, long, slender, slightly asymmetrical in section, arising from stem apophysis, usually a well to poorly marked internode between apophysial segment and hydrotheca; adcauline wall weakly convex, abcauline wall straight to weakly concave, a ring of tiny punctae near base of hydrotheca, a band of remnant tissue extending diagonally upwards into hydrotheca from desmocyte ring. Margin with 2 long, sharp triangular cusps separated by deeply scalloped embayments, demarcation between margin and hydrothecal body faint, operculum splits into at least 4 thin flaps.

Gonothecae large, thickly scattered throughout polysiphonic parts of stem and branches, laying along branch or in axil of two branches, cocoon-like, one side adnate to branch. Developing gonotheca flask-shaped, perisarc relatively thin, mature gonotheca cocoon-lilte, embedded in a meshwork of more or less parallel or entwined fascicular tubes. Empty gonotheca circular to bun-shaped in transverse section with a moderately thick, smooth internal rind of perisarc surrounded by a tight single or double row of fascicular tubes. Orifice terminal, facing outwards or upwards, but frequently obscured, shape variable from subcircular to vaguely quadrangular or scoop-shaped, sometimes surrounded by a short raised collar composed of several perisarcal rings. Operculum a sheet of tissue torn aside at the release of contents.

Perisarc of hydrotheca delicate, thinning markedly to margin.

Colour: Colony pale honey-yellow, distal parts and hydrothecae almost colourless.