Trigonostemon palustris R.Y.Yu & Welzen, 2020

4. Trigonostemon palustris R.Y.Yu & Welzen View in CoL , sp. nov. — sect. Trigonostemon — Fig. 4 View Fig , 5 View Fig ; Map 1 View Map 1

The species resembles the other endemic species in Palawan, T. victoriae , in the sepals being significantly larger than the petals in pistillate flowers, but it can be distinguished from the latter by the yellow, flat (vs dark red and revolute) petals and annular disc in both staminate and pistillate flowers (vs 5 lobes in T. victoriae ). — Type: Yu 260 (holo PNH; iso DLSUH, L), Philip- pines, Palawan Province, El Nido, trail to the Nakalit-kalit Waterfalls, 2 Apr. 2018 .

Small trees, c. 2 m tall; flowering branches terete, 3–3.7 mm diam, pubescent in young parts. Outer bark grey, 0.1–0.2 mm thick; inner bark 0.1–0.2 mm thick, red, sap red; wood pale yel- low. Stipules subulate or falcate, 0.7–1.4 mm long, caducous, base pubescent. Leaves: petioles terete, slightly thickening towards both ends, 3–7 cm long, 1.6–2 (middle part)– 3 mm (apex or base) diam, glabrescent; blade elliptic, 12–23 by 5.5–7.7 cm, chartaceous to coriaceous, base acute, 1–2 pairs of adaxial glands present, margin distantly serrate, teeth subulate, apex acuminate to caudate, upper side (somewhat dark) green, glabrous, lower side pale green, often slightly pubescent, particularly on venation; midrib flat or very slightly grooved above, elevated beneath, nerves 8–11 pairs, curved and connected near margin, veins and veinlets reticulate. Inflorescences bisexual or unisexual, terminal or axillary, racemose thyrses; main rachis 2–4.5 cm long, 0.6–1.2 mm diam, densely pubescent, few (up to 10) staminate flowers clustered per node, pistillate flowers single per node; involucral bracts as stipules; bracts triangular, 0.7–2.6 by 0.5–0.7 mm, pubescent on both sides. Staminate flowers 5–7 mm diam; pedicel 1.5–2 mm long, 0.3–0.4 mm diam, green, slightly pubescent; sepals orbicular to elliptic, 0.8–1.3 by 0.4–0.9 mm, light green, base connate, margin entire, apex rounded to acute, pubescent outside, glabrous inside; petals flabellate, 1.5–1.9 by 1.4–1.6 mm, yellow, base cuneate, margin entire, apex slightly bilobed, glabrous on both sides; disc annular, c. 0.2 mm diam (inner margin), c. 0.2 mm thick, yellow; stamens 3, androphore erect, 0.4–0.5 mm long, anthers ellipsoid, 0.3–0.4 mm long, divaricate at apex. Pistillate flowers 4–6 mm diam; pedicel 3.5–5 mm long, thickening towards the apex, 0.6–0.9 mm diam (apex), light greenish to pinkish, pubescent; sepals elliptic, 5–7 by 2–3.5 mm, pink, base connate, margin serrate, apex acumi- nate, with 3 main teeth; petals obovate to spathulate, 3.4–4.2 by 2.5–3.4 mm, yellow, base cuneate, apex rounded, sometimes slightly plicate, glabrous on both sides; disc annular, 2.2–2.6 diam, c. 0.1 mm thick; ovary 1.9–2 mm diam, glabrous, style 0.1–0.2 mm long, stigmas completely bifid, arms 0.7–1 mm long. Fruits light green, glabrous; sepals persistent, not much accrescent, green, stigmas persistent, pinkish.

Distribution — Philippines (Palawan, endemic).

Habitat & Ecology — Lowland forest edge, in swamps (hence the specific epithet).Altitude: c. 25 m. Flowering: February,April; fruiting: February .

Note — This new species was first brought to our attention by images published on Co’s Digital Flora of the Philippines ( Pelser et al. 2011 onwards), and we are grateful to the own- ers of the photos who gave us permission to re-use them in this article. The species has two relatively unusual characters: pistillate sepals being larger than petals and yellow petals in both staminate and pistillate flowers. It is the only species with yellow petals in sect. Trigonostemon . These charac- ters are only known to occur separately in a few species, e.g., T. victoriae (larger sepals than petals in pistillate flow- ers), and T. laevigatus and T. philippinensis (yellow petals), but they are all clearly different from this new species. The species is found to cohabit with ants ( Fig. 4i View Fig ; RYY pers. obs.).