Perennial herb, 15-40 cm, stems slender, ascending, branching above, not rooting, terete. Leaves sessile or up to ¾ mm petiolate, 4-17 by 2-6 mm, lanceolate or ovate to elliptic-oblong, apex rounded, base cuneate to rounded (or the upper ones sometimes cordate-amplexicaul), paler beneath; 3-4 main lateral veins, with reticulate branchings, uniting near margin and apex; reticulate venation ± marked, dense; laminar glands pale, large, often prominent, dense, punctate; intramarginal glands black, dense. Inflorescence 1-c. 10-flowered, cymose, monochasial after 2nd grade, lax; pedicels sometimes exceeding uppermost leaves, 3-6 mm in fruit. Flowers 8-10 mm ø, concave; buds ellipsoid, obtuse. Sepals 3-5½ by 1-1 ½ mm, free, imbricate, lanceolate to elliptic-oblong, obtuse to rounded, entire; laminar glands pale, punctate or shortly striate, few; submarginal glands all black or basal ones pale. Petals yellow, 5-6 by 2 mm, narrowly obovate or oblong-obovate, persistent; apiculus absent; laminar glands absent or few near apex, pale, punctate; marginal glands black, few, sometimes prominent. margin entire or with 1-2 subapical prominent glands; Stamens in 3 (abnormally 4-5) fascicles, c. 30, longest c. 4 mm, c. 5/6 as long as the petals, persistent; anthers yellow; gland black. Ovary c. 3 mm, ellipsoid; styles 3 (abnormally 4-5), l½ mm, shorter than ovary, divergent; stigmas scarcely capitate; placentas 3 (abnormally 4-5), axile. Capsule 4-5 by 3-4 mm, broadly ovoid to subglobose, longitudinally vittate. Seeds mid-brown, ½ mm, cylindric-ellipsoid, not carinate, densely shallowly reticulate-scalariform.
Asia-Tropical:, Philippines (Philippines ‒ present) Central: present Japan: present Luzon: present Pauai: present north: present north to southern Hokkaido: present
Taiwan (north and central), and Japan (north to southern Hokkaido), in Malesia: Philippines (Luzon, Pauai).
The Philippine plant resembles some of the specimens from Taiwan. The variation in that island, however, overlaps that of the Japanese H. pseudopetiolatum to such an extent that it is impossible to recognise H. taihezanense, even at varietal level.
Y. KIMURA - in Bot. Mag. Tokyo. 1940: 81
S. SUZUKI - in Masamune, Short Fl. Formosa. 1936: 141
R. KELLER - in Nakai & Honda, Nova Pl. Jap. 10. 1951: ff. 68, 69
S. SUZUKI - in Ann. Rep. Taihoku Bot. Gard. 1931: 158
Y. KIMURA - in J. Jap. Bot. 1939: 295
Y. KIMURA - in Nakai & Honda, Nova Fl. Jap. 10. 1951: 204