Homalomena selaburensis
Medium clumping evergreen, aromatic (reminiscent of lime peel) mesophytic herbs to 55 cm tall. Stem epigeal, erect, leafy, later the older parts leafless and decumbent with the active tip ascending. Leaves ca. 6 per module, ca. 8–10 together; modules subtended by a conspicuously 2-keeled prophyll up to 8 cm long; petioles up to 22 cm long, sheathing for ca. 1/3 their length, ascending to spreading, flexing slightly upwards at the 2–3 cm long pulvinus occurring ca. 2/3 along the petiole length, with 1/3 of the petiole lying distal to the pulvinus, petiole above the petiolar sheath D-shaped in cross section, with the distal-most ca. 6 cm shallowly dorsally grooved, the dorsal edges bluntly rounded, petiole dull reddish-brown, colour deeper towards the base, minutely scabridulous; petiolar sheath conspicuous, persistent, margins incurved except, sheath coloured as for petiole, or somewhat darker; blade up to 20 x 13 cm; cordiform, posterior lobes parallel to somewhat incurved, rounded, sinus obtuse, apex acute, tubular-mucronate for ca. 2 mm, highly polished medium green adaxially, matte subglaucous pale green with conspicuous darker pellucid striate interprimary venation especially near the blade margin, these more conspicuous on younger leaves; midrib moderately conspicuous, impressed adaxially, rounded-raised abaxially; primary lateral veins up to 8 per side, the lower 3 arising ± simultaneously and associated with the posterior lobes, impressed adaxially, slightly raised abaxially; interprimary veins of two types, one type alternating with primaries and only slightly less conspicuous, the second type comprising conspicuous pellucid darker veins, these very numerous and sometimes branching just after they exit the midrib; secondary and tertiary venation 6 invisible. Inflorescences up to 7 together, produced sequentially in a simple synflorescence; peduncle rather stout, up to 15 cm x 5 mm, medium green heavily speckled reddish brown, the colour intensifying towards the base, spreading with the inflorescence nodding at anthesis, inflorescence with spathe opening ventrally relative to the peduncle; spathe spreading at pistillate anthesis, broadly ovate-ellipsoid, not constricted, ca. 6.5 x 3 x 1.5 cm deep at anthesis, tipped with a rostrate mucro 5 mm long, margins reflexing during anthesis, spathe medium green in bud, in bid the exterior bright medium green, glossy, at anthesis exterior green and interior greenish white with numerous minute paler glands. Spadix ca. 2/3 length of the spathe, 4 cm long including the stipe; stipe obliquely inserted on the peduncle, oblique, ca. 5 mm long on its longest side, ca. 3 mm diam., glossy very pale green; pistillate flower zone ca. 1/3 the length of the spadix, ca. 1.2 x 0.8 cm; pistils somewhat loosely arranged, almost cylindrical, ca. 1 x 0.6 mm, pale green; style very short, slightly narrower than the ovary; stigma almost equalling the 3–4-staminate, stamens each with two anthers; stamens elongate-globose, connective embedded and 6 invisible; thecae opening by a conspicuous lateral slit. Infructescence pendent, spathe fully persistent and turning deep green, ellipsoid, ca. 5.5 3 2 cm; fruit and seeds not observed.
Homalomena selaburensis differs from all other species of the Homalomena Supergroup by the combination of matte, scabridulous petioles and peduncles, inflorescences nodding at anthesis, and leaf blades adaxially highly polished. It is the only limestone-associated species of the Homalomena Supergroup so far known.
Homalomena selaburensis is restricted to the forested Karst limestone in Serian District, on which ecology numerous other aroids are endemic, including Schismatoglottis confinis S.Y.Wong, S. convolvula P.C.Boyce, S. simonii S.Y.Wong, but with the majority undescribed. So far H. selaburensis has not been located from the alkaline basalts of Ranchan, on the outskirts of Serian town, on which several other otherwise limestone-associated aroids occur (e.g., Piptospatha viridistigma P.C.Boyce, S.Y.Wong & Bogner, Pothos insignis Engl., Schismatoglottis ranchanensis S.Y.Wong). A collection from the basalts of Gunung Ampungan has yet to flower in cultivation, but is a close match for Homalomena selaburensis. Gunung Ampungan has several otherwise limestonerestricted species present, including Alocasia reversa Ridl., Schismatoglottis confinis, and S. simonii.
Homalomena selaburensus occurs as a lithophyte in deep humus pockets on or at the base of Karst limestone formations under somewhat open perhumid lowland forest at between 40–120masl.