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

Medium-sized clumping obligate rheophytes to 30 cm tall. Stem condensed, erect, ca. 5 cm long x ca. 2 cm in diam., mostly obscured by the dense leaf bases, with copious strong roots and often with stilt-roots emerging from between the leaf bases. Leaves many together, petioles suberect with blades slightly arching; individual modules with several leaves, modules subtended by a linear-triangular 2-keeled prophyll to 7 cm long and ca. 5 mm wide, initially prophyll green, but soon decaying; petiole 9–14 cm long, weakly D-shaped in cross section, ca. 3 mm wide 3 ca. 2.5 mm high, dorsal edges slightly raised, sheathing at the extreme base, medium green; petiolar sheath with wings extended into a narrowly triangular ligular portion 5–8 cm long, ligule soon marcescent and shedding to leave a short collar of papery tissue; blade softly coriaceous, elliptic, 14–22 cm long 3 4–5.5 cm wide, base cuneate, apex acute, apiculate for ca. 5 mm, adaxially semi glossy dark green, glossy pale abaxially; midrib abaxially prominent, somewhat paler than the rest of the blade, adaxially bluntly raised; primary lateral 4 or 5 adaxially weakly defined veins on each side, these diverging at ca. 30°; interprimary veins slightly darker than the primaries in appearance; secondary venation adaxially invisible. Inflorescence solitary or up to three together alternating with foliage leaves, subtended by a ca. 7 cm long, very narrowly triangular somewhat leathery cataphyll; peduncle slender, erect, equalling to slightly exceeding the petioles up to 14 cm long, ca. 3 mm diam., terete, medium green, inserted slightly obliquely on the spathe; spathe broadly ovate with a long acuminate tip, not constricted, 8–9 cm long, lower part campanuliform at anthesis, medium green, ultimately persistent through fruiting, limb glistening white, apiculate for up to 1 cm, apicule distally green; limb gaping at pistillate anthesis, caducous from the junction of the spathe limb and the persistent lower part, limb falling more-or-less intact to leave the narrowly campanuliform persistent lower spathe, with a scarred regular rim. Spadix tapering cylindric, ca. 4.5 cm long 3 ca. 7 mm in diam. (widest part), usually fertile to the tip; pistillate flower zone oblong cylindric, about the same width as the other fertile parts of the spadix, comprising slightly less than 1/4 of the spadix, ca. 1 cm long, 2–3 rows of trapezoidal to hexagonal glossy white staminodes at the base; pistils subglobose, truncate, c. 1.1 mm in diam., pale green; stigma sessile, slightly impressed, hexagonal, papillose, wider than ovary, pale green; sterile interstice cylindric, equalling the pistillate zone in width, ca. 1.3 cm long, with several dense whorls of hexagonal staminodes, these ca. 1.3 mm in diam., glossy white; staminate flower zone ca. 1/2 of total spadix length, ca. 2 cm long, lower part equalling the width of the sterile interstice, fertile to the tip, or the tip furnished with two or three staminodes, glossy white; staminate flowers densely packed, comprised of two stamens, ivory, ± oblong, with the long sides parallel to the spadix axis, ca. 2 x 1 mm, connective with the surface with a narrow longitudinal groove; thecae ellipsoid, imperceptibly embedded in the ends connective, each ca. 0.5 mm long; thecae horns two per stamen, ca. 3mm long, stiff, semi-translucent, appressed to the stamen during pistillate anthesis, becoming semi-erect and then erect at staminate anthesis, and then producing an irregular mass of pollen from the tip. Infructescence an erect splash-cup. Fruiting spathe campanuliform, ca. 1.5 cm long x c. 1.5 cm wide, medium green with a scar along the rim; immature fruits prismatic globose, c. 2 mm tall and in diam., dark green; stigmatic remains sunken, dark brown; ripe fruits deliquescing into a pale whitish slime; seeds ellipsoid, longitudinally very finely ridged, on one end with an elongate, curved micropylar appendage.