Derris rubricosta Boonprajan & Sirich., 2024

Boonprajan, Punvarit, Leeratiwong, Charan & Sirichamorn, Yotsawate, 2024, From morphology to molecules: A comprehensive study of a novel Derris species (Fabaceae) with a rare flowering habit and reddish leaflet midribs, discovered in Peninsular Thailand, PhytoKeys 237, pp. 51-77 : 51

Derris rubricosta Boonprajan & Sirich. sp. nov.

Figs 1 , 2 , 3

Type.

Thailand. Songkhla, Sadao district, Padang Besar sub-district, Pha Dam Forest Ranger Unit , Ton Nga Chang Wildlife Sanctuary , c. 150 m elevation, GPS coordinate 6°47'16.7"N, 100°13'51.8"E, 22 January 2019, C. Leeratiwong 19-1666 (holotype BKF!; isotypes K!) .

Diagnosis.

The species has several autapomorphies distinguishing it from other Derris species. It is the only species that has reddish midribs on the lower surface of mature leaflets. Its style is sericeous at the base and gradually becomes glabrous apically (vs. thinly hairy at the base and mostly glabrous throughout in other Derris species). Derris rubricosta has prominent hairs below the anthers (vs. glabrous anthers in all other Derris species). It is morphologically similar to D. pubipetala Miq., but differs by its leaflet midrib colour (reddish vs. green), number of leaflets er leaf (9-11 vs. 5-9), colour of its corolla (pale pink to pink vs. white), wing petal margin (straight vs. revolute), stamen filament indumentum (sparsely hairy vs. glabrous), indumentum presence below the anthers (present vs. absent), floral disc shape (indistinct to more-or-less 10-lobed vs. annular).

Description.

Woody climber. Bark pale brownish-gray to gray, lenticellate. Leaves with 9-11 leaflets, reddish when young, chartaceous to sub-coriaceous. Stipules caducous (not present on herbarium specimens); petiole 6-10.8 cm long, grooved above, thinly strigose to almost glabrous; rachis 10-18 cm long, grooved above, thinly strigose to glabrous; pulvinus 9-15 mm long, thinly strigose; stipellae absent; terminal leaflet elliptic to obovate or narrowly oblong, 10-18.3 × 3.0-4.3 cm, length/width ratio 3.2-4.3, base cuneate, apex acuminate, acumen 7.2-18 mm long, emarginate, upper surface glabrous but slightly strigose along midrib and lateral veins, lower surface glabrous to sparsely strigose along midrib, lateral veins and lamina, sometimes slightly strigose to glabrous at the margin, midrib (reddish on fresh mature leaflets) and secondary veins slightly raised or flat above, raised below, 7-9 each side of the midvein, 0.7-2.7 cm a part, curving towards the apex and almost reaching the margins, sometimes anastomosing near the margins, tertiary venation reticulate, pulvinus 5.0-6.5 mm long, sparsely strigose; lateral leaflets mostly like the terminal one, narrowly elliptic to obovate, rarely ovate, 10-18.8 × 3-4.4 cm, length/width ratio 3-4.3; pulvinus of petiolules 4.5-6.5 mm long, sparsely strigose to sericeous. Inflorescence a pseudoracemes or pseudopanicle, axillary or terminal, 40-50 cm long; peduncle 2-7 cm long, lenticellate, strigose; bracts subtending inflorescence triangular, 2-2.6 × 1.8-2.5 mm, outside with some hairs at base and along margin apically, inside glabrous; bracts subtending lateral branches triangular, ovate, 2-2.5 × 1.8-2.4 mm, outside with some hairs at base and along margin apically, inside glabrous; lateral branches 3.4.-15 cm long, sparsely strigose at base, lenticellate; bracts subtending brachyblasts ovate-triangular, 1-2.5 × 0.8-1.4 mm, outside with some hairs at base and along margin apically, inside glabrous. Brachyblasts knob-like to elongate-cylindrical, 1-12 mm long, 2-flowered, strigose; bracts subtending flowers ovate-triangular, 0.7-0.9 × 0.7-1 mm, outside sparsely hairy at base and along margin, inside glabrous; pedicels 3.5-5.2 mm long, strigose; bracteoles 2, at base of calyx, ovate, semi-circular, orbicular to narrowly triangular, 0.6-0.9 × 0.5-0.7 mm, outside sparsely strigose, with some hairs along the margin, inside glabrous. Calyx red- to maroonish, cup-shaped 3.4-4.2 mm long, outside sparsely strigose, with some hairs along the margin, inside glabrous; tube 3-3.2 mm long; upper lip with 2 short lobes, 0.2-0.4 × 1.5-2 mm; lateral lobes short-triangular, 0.2-0.6 × 0.7-1 mm; lower lobes triangular 0.3-1.3 × 0.8-1.2 mm. Corolla pale pink to pink; standard orbicular or broadly ovate, with a greenish-yellow spot at the base on the inner surface, 8.5-10 × 8.6-9.3 mm, apex emarginate, basal callosities absent, outside hairy from the middle part to apex, inside with some hairs near apex, claw 1.5-2.8 mm long; wings elliptic to narrowly ovate, 7.3-8.2 × 3.1-4 mm, apex obtuse, upper auricle indistinct, pubescent, 0.5-0.9 mm long, lower auricle absent, lateral pocket 1.4-2.2 mm long, outside hairy in the middle part of the petal to the apex, inside hairy near the apex, claw 1.8-3.5 mm long; keels boat-shaped 7-7.8 × 2.3-3 mm, apex retuse, upper auricle pubescent, 0.5-1 mm long, lower auricle absent, lateral pocket 1-2.1 mm long, outside and inside hairy near the apex, sometimes also with sparse hairs along the veins ventrally, claw 1-2.9 mm long. Stamens 10, monadelphous, 2.8-4.6 mm long, free part 1.5-3.1 mm long, sparsely hairy, anthers 0.5-0.6 × 0.2-0.3 mm, with some basal hairs. Disc indistinct, or more or less 10-lobed, glabrous. Ovary 3.5-5 mm long, sericeous; stipe usually indistinct, sericeous; style 5.6-7.4 mm long, sericeous at the base and gradually become glabrous apically. Pod and seeds unknown.

Phenology.

Flowering from November-February and fruiting possibly from March-April.

Vernacular names.

"Khruea lai leeratiwong" (เครือไหลลีรติวงศ์) means “Leeratiwong’s Derris ", in Thai, in honor of Associate Professor Dr. Charan Leeratiwong, who discovered and collected the type specimens.

Etymology.

The specific epithet refers to the striking reddish colour of the midrib of the mature leaflets which has never been found in other species of Derris .

Distribution.

Peninsular Thailand: Songkhla (Rattaphum district, Sadao district) (Fig. 4 ). Estimated population of more than 2,500 mature individuals were found during field survey between 2019 and 2022 in its type locality and nearby areas.

Habitat and ecology.

Usually near streams, in semi-shaded to fully exposed areas of tropical evergreen rainforest. The species, especially in the type locality, thrives on sandy or sandy-loam soils.

Proposed IUCN conservation assessment.

This new species is only known from two locations in Songkhla province. The estimated number of mature individuals might be more than 2,500 but less than 10,000. The Area of Occupancy (AOO) is about 2,000 km2. Although its type locality and overall distribution are located within conservation areas, the species is still threatened by human disturbance. Therefore, we provisionally assess its conservation status to be "Vulnerable (VU), B2 b(ii) c(ii)", following the criteria of the IUCN Standards and Petitions Committee (2022, v. 15.1)

Representative specimens examined (paratypes).

Thailand. Songkhla: Rattaphum district , Kamphaeng Phet sub-district, 27 October 2021, Sirichamorn Y. and Boonprajan P. YSM2021 - 15 (BKF!); Sadao district, Padang Besar sub-district, Pha Dam Forest Ranger Unit, 27 October 2021, Sirichamorn Y. and Boonprajan P. YSM2021 - 14 (BKF!) .

Figures

Figure 1. Derris rubricosta, sp. nov. A habit and habitat B leaves C stem D young reddish leaflets E reddish midribs of mature leaflets F, G close-up of midrib on adaxial and abaxial surface respectively H inflorescences and foliage I, J close-up of inflorescence, showing flower buds and brachyblasts K close-up of flower and buds. All photos were taken at Pha Dam Forest Ranger Unit in Songkhla province. Photos by Punvarit Boonprajan (A, B, D - G) and Charan Leeratiwong (C, H - K).

Figure 2. Comparative macro- and micro-morphological characters of leaflets and flowers of Derris rubricosta (A, A 1 - A 10) and D. pubipetala (B, B 1 - B 10) A, B a branch with leaves and inflorescences A 1, B 1 outer surface and A 2, B 2 inner surface of standard petal A 3, B 3 outer surface and A 4, B 4 inner surface of keel petals A 5, B 5 outer surface and A 6, B 6 inner surface of wing petals A 7.1, B 7.1 stamens and A 7.2, B 7.2 close-up stamens A 8.1, B 8.1 pistil and A 8.2, B 8.2 close-up pistil apex A 9, B 9 adaxial and A 10, B 10 abaxial leaflet surfaces. Photos by Charan Leeratiwong (A, B) and Punvarit Boonprajan (A 1 - A 10, B 1 - B 10). Scale bars: 1 mm.

Figure 3. D. rubricosta A inflorescence with leaf B close-up of inflorescence C flowers (top and side view) D outer surface and E inner surface of standard petal F outer surface and G inner surface of keel petals H outer surface and I inner surface of wing petals J staminal sheath K anthers L pistil M adaxial and N abaxial leaflet surfaces. Drawn by Punvarit Boonprajan from C. Leeratiwong 19 - 1666 (BKF). Scale bars: 5 mm (A, B); 1 mm (C-N).

Figure 4. Collection sites of the new Derris samples, represented by a yellow square (flowering specimen) and light-blue triangle (specimen without flowers) and D. pubipetala (orange circles) in Peninsular Thailand.