Aridarum orientale S. Y. Wong, P. C. Boyce & S. L. Low

Medium-sized obligate rheophyte 10 – 35 cm tall. Stem somewhat condensed, suberect, later to c. 10 cm long, 1.5 cm in diameter. Leaves up to 15 together, petioles erect with blades arching; petiole 4 – 17 cm long, 1.5 – 3 mm in diameter, very weakly D-shaped in cross section, weakly channelled dorsally, with the edges rounded, sheathing at the extreme base, medium green; petiolar sheath with wings extended into a narrowly triangular ligular portion 3 – 6 cm long, this ligule soon deliquescing; blade coriaceous, elliptic, 6 – 16 cm long × 2 – 5 cm wide, base cuneate, apex acute, shortly acuminate and apiculate for 8 – 10 mm, adaxially semiglossy dark green, paler abaxially; midrib abaxially and adaxially prominent; primary lateral veins 4 – 5 on each side, diverging at c. 30° from the midrib, adaxially prominent; interprimary veins very few, much less prominent than primaries and not visibly reaching the midrib or blade margins; secondary venation obscure; tertiary venation adaxially obscure, abaxially forming a slightly darker irregular reticulum. Inflorescence solitary, subtended by a 6 – 9 cm long very narrowly triangular membranous cataphyll. Peduncle mostly shorter than the petioles (exceptionally, longer in environmentally dwarfed individuals), 9 – 15 cm long, terete, medium green. Spathe broadly ovate, not constricted, 4 – 5.6 cm long, lower part green and ultimately persistent at fruiting, the remainder white, gaping and caducous by acroscopic deliquescence from the junction of the spathe limb with the lower, persistent portion during anthesis, spathe apiculate for up to 1 cm, apicule distally green. Spadix subcylindric (1.5 – )2 – 3 cm long, c. 0.6 cm in diameter; pistillate flower zone comprising c. 1/4 of the spadix, obliquely inserted on peduncle and subtended by a zone of large, weakly rhomboidal, white staminodes, ventral side of pistillate zone 8 – 10.9 mm long, dorsal side 3.8 – 5.6 mm long; pistils subglobose, truncate, c. 2 mm diameter, green; stigma subsessile, discoid, papillose, slightly wider than the ovary, white; interpistillar staminodes absent; sterile interstice composed of 2 or 3 clavate-rounded sterile anthers, white; staminate flower zone accounting for slightly less than 1/2 of the entire spadix length, 6 – 9.6 mm long × 4.5 – 6.8 mm wide; staminate flowers comprised of a single stamen, stamens more or less circular in plan view, with a deep suture between the thecae, comparatively large, c. 2.5 × 2 mm, connective centrally impressed with the margins forming a convex, raised, rounded rim, this smooth, occasionally slightly ridged, the whole somewhat kidney bowl-shaped; thecae globose, c. 1 mm long, displaced to the proximal (with respect to the spadix axis) side of the stamen with distal-pointing horns; thecae horns c. 0.5 mm long, stiff, stout; appendix c. 1/3 of the entire spadix, 4 – 6.6 mm long, bluntly tapering; appendix staminodes comprised of 1 – 3 branched knobbly sterile stamens, those at the base tending to be larger (up to 2 mm long), white. Fruiting spathe broadly obconic, c. 1 cm in diameter, and tall, subtending a ± globose cluster of berries, medium green with a conspicuous pale brown scar from the spathe limb abscission; berries globular, c. 3 mm in diameter, crowned with old stigma remnants, many-seeded; seeds c. 2 mm long, 0.6 – 0.7 mm in diameter, narrowly ellipsoid, dark brown, slightly longitudinally ribbed, with a long curved translucent micropylar appendage 1.2 – 1.5 mm long, the appendages intertwined in the upper part of the berry.