Helicteres ubonensis Chantar. & Kantachot, 2024

Helicteres ubonensis Chantar. & Kantachot View in CoL , sp. nov. — Fig. 1–2 View Fig View Fig

Etymology. The specific epithet refers to the collections from Ubon Rat- chathani province where the species was discovered.

Typical of this species are narrowly elliptic-oblong leaves. Corolla purplish white or pinkish. Capsule pointed as beak at the apex and surface covering with stellate hairs. — Type: P. Chantaranothai , C. Kantachot & P. Kludwong 2021-150 (holo KKU; iso AAU, QBG), Thailand, Khong Chiam , Napho Klang, along trail to Soi Sawan Waterfall, 10 Aug. 2019 .

Shrub, 1–2 m tall; twigs erect and some ascending, terete, young twigs brownish, glabrescent; twigs blackish, glabrescent; bark thick with fibres. Leaves spiral, narrowly elliptic-oblong, (8–) 10–15 by (1–) 2–3 cm, chartaceous, apex acute or acuminate, base cuneate or obtuse, margin entire, upper surface green, glabrous or glabrescent, lower surface pale green, with stellate hairs; midrib prominent on the lower surface; basal veins 3; lateral veins (3–)5–8 pairs; petioles 4–9 mm long, terete, hairy; stipules caducous. Inflorescences axillary or terminal, cymes, epicalyx present; peduncle 4–5 mm long, hairy. Flowers valvate, with short pedicels. Calyx campanulate, with 5 lobes, lobes unequal, green, hairy. Petals 5, free, spathulate, 7–9 by 4–5 mm, purplish white or pinkish. Androgynophore c. 5 mm long. Stamens 10, alternating with 5 staminodes, filament column glabrous; anther c. 0.5 mm long. Stigma 5, pointed apically. Ovary superior, surrounded by the filament column, longitu- dinally 5-lobed, hairy; style c. 1 mm long; ovules numerous, 8 per locule. Fruit capsular, cylindric, straight, pointed at the apex,2.5–3.5 by 0.7–1 cm, fruit stalk 2–6 mm long; young fruit green, mature fruit brown, with stellate hairs. Seeds rhomboid, 2–3 by 1.5–2 mm, dull black.

Distribution — Thailand (Ubon Ratchathani: Khong Chiam, Soi Sawan Waterfall and Pha Taem National Park).

Habitat & Ecology — In open space on rock platform with dry evergreen forest. Flowering and fruiting at least in July–October.

Vernacular name — Khi on ging dum (ขี้อ้นกิ่งดำ�).

Additional collections studied (paratypes). S. Poompo 10 (deposited at Department of Biological Science Herbarium , Ubon Ratchathani University ), Thailand, Ubon Ratchathani, Khong Chiam , Huai Phai, Pha Taem National Park, s.d .; C. Kantachot 2020-32 (KKU), Thailand, Ubon Ratchathani, Khong Chiam , Napho Klang , Soi Sawan Waterfall, along Sae Soi creek, 30 July 2020 .

Notes — Helicteres ubonensis is similar to H. angustifolia L. but differs in having narrow leaves, which are more or less oblong or elliptic-oblong, twigs brownish or blackish. It is also distinctive in the apically narrowed to pointed stigma, absence of setose hairs on the capsule surface and the capsule apex beaked ( Table 1).

NEW KEY TO THE SPECIES OF HELICTERES FROM THAILAND

Because of the discovery of several new species and new records, a new identification key to the species of the genus Helicteres for Thailand is provided:

1. Leaf margin entire or rarely with a few minute teeth near apex....................................... 2

1. Leaf margin serrate or dentate from base........... 9

2. Stems prostrate............................... 3

2. Stems erect or ascending....................... 4

3. Upper surface of leaves hairy; basal veins 3............................................ H. oblongifolia View in CoL

3. Upper surface of leaves glabrous; basal veins 5........................................... H. prostrata View in CoL

4. Inflorescence a lax thyrse............. H. thailandica View in CoL

4. Inflorescence a short cyme...................... 5

5. Leaf margin entire. Stigma flattened, slightly 5-lobed..................................... H. angustifolia View in CoL

5. Leaf margin entire or slightly serrate near apex. Stigma simple, narrowed to a point or divided into 5 teeth.... 6

6. Young twigs glabrous or sparsely hairy............. 7

6. Young twigs hairy.............................. 8

7. Leaves lanceolate or oblong-lanceolate. Capsule with vil- lous hairs.......................... H. lanceolata View in CoL

7. Leaves narrowly elliptic-oblong. Capsule without villous hairs.............................. H. ubonensis View in CoL

8. Leaves coriaceous, scabrous on upper surface. Apex of capsule without beak..................... H. lanata View in CoL

8. Leaves chartaceous, glabrous on upper surface. Apex of capsule with beak..................... H. geoffrayi View in CoL

9. Leaves ovate, broadly ovate to more or less rounded 10

9. Leaves oblong-lanceolate or oblong-ovate......... 11

10. Capsule twisted. Lower surface of leaves glabrescent or scabrous............................... H. isora View in CoL

10. Capsule not twisted. Both surfaces of leaves with soft hairs.................................. H. viscid

11. Leaves chartaceous. Calyx View in CoL less than 1 cm long. Capsule 1.5–2 cm long........................ H. elongata View in CoL

11. Leaves coriaceous. Calyx View in CoL more than 1 cm long. Capsule 2.5–5 cm long......................... H. hirsuta View in CoL