Sophora phulangkaensis Mattapha, K.Khamm. & Suddee, 2024

Sophora phulangkaensis Mattapha, K.Khamm. & Suddee , sp. nov. — Fig. 3 View Fig , 4 View Fig

Closely related to S. exigua Craib ,from which it differs by being a small shrub 0.5–2 m tall (vs undershrub up to 0.5 m tall in S. exigua ), with sparse to dense hairs on midrib and margins of leaf blade (vs densely tomentose in S. exigua , particularly when young), presence of bracteoles (absent in S. exigua ), the standard 15–16 mm long ( 18–20 mm long in S. exigua ), filaments hairy at base with hairy anthers (glabrous in S. exigua ), ovary densely strigose (tomentose in S. exigua ) and longer pods ( 7–13 cm long vs 5–7 cm long in S. exigua ). — Type: Khammongkol 211 (holo BKF; iso BKF!), Thailand, Nakhon Phanom, Ban Phaeng district, Phu Langka National Park, summit plateau,near golden stupa, N17°58'12" E104°07'02", 550 m, 24 Mar. 2020, fl. For paratypes see below.

Etymology. The specific epithet refers to the name of Phu Langka National

Park, where the species was discovered.

Small shrub, 0.5–2 m tall; young twigs densely hairy with strigose hairs. Leaves imparipinnate; petioles 4 –8 cm long, densely strigose, grooved above; stipules lanceolate, c. 1 by 0.5 mm, outside densely strigose, early caducous; rachis 10–18.5 cm long; ultrajugal part up to 2.5 cm long. Leaflets 7–15; petiolules 1–2 mm long, densely strigose; lamina elliptic or elliptic-oblong, terminal leaflet sometimes obovate, 1–3 by 0.8–1.8 cm in flower, 5–8 by 2.5–3.5 cm in fruit, apex retuse, acute or obtuse, base obtuse of broadly cuneate, margins entire, upper surface glabrous, lower surface sparsely to densely hairy on midrib and margins, otherwise glabrous or with a few sparse hairs; secondary veins 5–10 on each side of midrib, raised on both sides, anastomosing near margin distinct; stipels absent. Inflorescences racemose, terminal, 12–20 cm long, leaf-opposed, with strigose hairs throughout. Flowers pale purplish white to purplish pink, standard with a dark purple blotch at base above claw on the dorsal face, glabrous; bracts and bracteoles triangular, very minute, early caducous. Pedicels including the articulate section 4–8 mm long, articulated near apex, hairy. Calyx tubular, pale pinkish purple; tube 5–8 mm long; lobes 5, broad, 1–1.5 by 2.5–3 mm, apex acute to rounded, margin hairy, hairy outside, glabrous inside. Corolla : standard petal spathulate, 15–16 mm long, blade obovate, curved upwards, 5–6 by 6–7 mm, apex emarginate, base without callosities, tapering attenuately into the claw, glabrous on both sides, claw 9–10 mm long; wing petals suboblong, 11–13.5 mm long, blade 8.5–9 by 2.5–3 mm, slightly constricted below the middle, base auriculate, with a hook-like auricle of c. 1 mm long on each side, apex rounded, outside with lunate sculpturing on the lower half, glabrous on both sides, claw 4–4.5 mm long, flattened; keel petals oblique oblong, 11–13 mm long, blade 6.5–7 by 2.5–3 mm, apex rounded to subtruncate, glabrous on both sides, claw 4.5–5 mm long, flattened. Stamens 10, shortly joined at base, distally free; filaments 10–12 mm long, flattened, hairy at base; anthers oblong, c. 0.5 by 0.2 mm, hairy. Ovary densely strigose, 8–9 mm long; stipe c. 2 mm long; style c. 3 mm long, glabrous. Pods submoniliform, constricted between seeds or slightly septate, 7–13 by 0.5–0.7 cm, densely and shortly adpressed hairy, apex often pointed. Seeds (1–)2–5 per pod, ellipsoid or oblong, 7–7.5 by 3–4 mm.

Distribution — Endemic to Thailand, only known from the type locality.

Ecology — Grassland on sandstone plateau. Flowering: March; fruiting: April, May.

Vernacular name — Phit sanat phu langka (พิษนาศน์ภูลังกา), the name is given by the authors.

Conservation status — According to the IUCN threatened criteria ( IUCN 2022), the species has a small population size with few individuals found, but in a protected area. We assess it here as Data Deficient (DD) due to the inadequacy of the distribution information.

Additional specimens examined ( paratypes). NORTHERN, Mattapha s.n. (BKF, KKU), Nakhon Phanom [Ban Phaeng district, Phu Langka National Park, c. 200 m, 14 July 2012, fr.; Kerr 8427 (BK [ SN212294 ]!, K [K000759742!]), Nakhon Phanom, precise locality not known, c. 200 m, 11 Feb. 1924, fl.

Notes — Sophora phulangkaensis is characterised by being a small shrub up to 2 m tall, leaves with 7–15 leaflets, racemes up to 20 cm long, leaf-opposed, tubular calyx with hairs outside, obovate standard without basal callosities and glabrous on both sides, wing petals with a hook-like auricle c. 1 mm long on each side at base, submoniliform fruits with densely and shortly adpressed hairs.

The morphological characters support placement of the species in sect. Rubriflorae : flowers violet, pedicels articulated, standard with a long claw, wing petals at base sagittate or hastate and at base with a hook-like auricle; and stamens shortly joined at base, distally free. Moreover, the calyx has prominent lobes and the spathulate standard petal curves strongly upwards (as in sect. Rubriflorae ). In addition, S. phulangkaensis has stipules that are early caducous; by contrast, Tsoong & Ma (1981) and Ma (1990) reported that sect. Rubriflorae lacks stipules.