Strobilanthes namkadingensis is distinguished from all the previously known species of Laos and its surrounding countries including China, Cambodia, Thailand and Vietnam clearly by a combination of 6–32 flowered spikes up to 10.5 cm long, yellow corolla, the absence of long white hairs on the bracts and 4–6-seeded capsule. In the region, S. namkadingensis is similar to Strobilanthes squalens S.Moore of Vietnam and Sericocalyx thailandicus Bremek. of Thailand in having yellow corolla and long-beaked floral bracts, but distinguished by its long spikes (vs. less than 3 cm long), broader floral bracts (obovate-elliptic to broadly elliptic vs. lanceolate to ovate-lanceolate), smaller corolla (1.9–2.1 cm long vs. less than 1.7 cm long), and the absence of long white hairs on the bracts.

Figure 1. 

Locality of Nam Kading National Protected Area. White circle indicates where we found Strobilanthes namkadingensis Soulad. & Tagane.

Figure 2. 

Strobilanthes namkadingensis Soulad. & Tagane. A flowering branch B abaxial leaf surface C inflorescence D flower E side view of corolla F floral bracts G corolla opened out H fruit with calyx J longitudinal section of capsule showing seeds (from Tagane et al. L426, FU). All scale bars: 5 mm.

LAOS. Bolikhamxay Province, Nam Kading National Protected Area, in semi-evergreen forest, beside a dried rocky stream, 18°12'17.9"N, 104°33'34.5"E, alt. 146 m, 26 Dec. 2016, with flowers and fruits, Tagane S., Yahara T., Zhang M., Okabe N., Souladeth P., Sengthong A., Chayer S. L426 (holotype-HNL!, isotypes-FOF!, FU!, K, KYO!, P).

Anisophyllous shrub, 1.5 m tall. Stem terete, densely covered with white hairs, pale yellow green when dried. Leaves slightly unequal in each pair, petiolate; blade broadly elliptic, ovate-elliptic, (0.7–)5.5–11 × (0.2–)2.2–4.5 cm, apex acuminate, base cuneate, briefly decurrent onto petiole, margin shallowly crenate, chartaceous, pale yellow green adaxially, light pale yellow green abaxially, sparsely strigose and scabrous on both sides, densely covered with cystoliths adaxially; midrib prominent on both surfaces, secondary veins 6–8 pairs, prominent on both surfaces, tertiary veins scalariform-reticulate, faintly visible to invisible; petiole 0.5–1.3 cm long, scabrid adaxially, glabrous abaxially, margin ciliate. Inflorescences spicate, terminal and axillary, (2–)3–10.5 cm long, 6–32-flowered; outer (inflorescence) bract narrowly elliptic-ovate, 1.4–2.1 × 0.4–0.5 cm, apex acute to acuminate, sessile, shortly puberulent adaxially, sparsely with short stiff hairs at margins and on midveins on both surfaces; floral bracts obovate-elliptic to broadly elliptic, ca. 1.7 × 0.7 cm long, apex caudate, acumen up to 0.8 cm long, persistent, pale yellow green, sparsely pilose with glandular hairs adaxially, shortly puberulent, with grand-tipped hairs abaxially, margin ciliate with large-celled white hairs; bracteole 2, linear, 5–7 mm long, glandular hairy. Calyx lobes 5, linear, ca. 5–9 mm long, apex acute, slightly accrescent in fruit, upper three and lower two calyx lobes are fused ca. 2 mm from the base, covered with cystoliths adaxially, glandular hairy abaxially. Corolla yellow, funnel-shaped, 1.9–2.1 cm long, 0.8 cm in diam., membranaceous, hairy with short erect hairs outside, pilose with long white hairs inside of tube, corolla lobes 5, elliptic to suborbicular, ca. 3.8 × 3.1–3.8 mm, apex rounded. Stamens 4, didynamous; the shorter pairs of filaments ca. 1.5 mm long, with a few white hairs; the longer ones 5–6.5 mm long, pilose with long white hairs except upper 2/5, base of filaments adnate to corolla tube; anthers ca. 2–2.2 mm long, dorsifixed, attached lower 1/3 part of anther (monadelphous). Style 1.2 cm long, sparsely pilose, stigma ca. 2 mm long, glabrous. Capsule narrowly ellipsoidal, 8.4–10 mm long, ca. 2.8 mm in diam., glandular hairy, 4–6-seeded. Seeds spirally arranged on free-central placenta, suborbicular, 2 mm height, 1.8 mm width, 0.2 mm thick, strongly flattened, light yellow brown, glabrous.

Laos, Bolikhamxay Province (so far known only from Nam Kading National Protected Area).

Strobilanthes namkadingensis is found in semi-shaded understory of semi-evergreen forest beside a dried stream; at alt. 146 m. The flowering and fruiting specimen was collected in December.

Tagane et al. L426: LC257983 (rbcL), LC257984 (matK) and LC257953 (ITS).

This specific epithet namkadingensis refers to the type locality.

Data Deficient (DD) (IUCN 2012). Only one individual was found along a dried rocky stream beside road. The individual grows in a protected area of Nam Kading National Protected Areas, but the habitat is close to a road and can be easily affected by human disturbance from the road. Further intensive field surveys are needed to evaluate its conservation status.

Bremekamp (1944) treated the species having a yellow corolla and 4–8 seeded capsule as Sericocalyx Bremek. and the new species belongs to this group. However, Moylan et al. (2004) demonstrated that Sericocalyx is polyphyletic in the subtribe Strobilanthinae, based on phylogenetic analyses using ITS and trnL-F sequences and morphology. Therefore a single monophyletic Strobilanthess.l. is accepted (Moylan et al. 2004, Deng et al. 2006) and the new species is here described as a species of Strobilanthes. The BLAST similarity search based on the ITS sequence of S. namkadingensis resulted in homology as high as 543/562 bp (including 17 gaps) and 532/562 bp (including 19 gaps) with the sequence of S. chinensis (Nees) J.R.I.Wood & Y.F.Deng (synonym, Sericocalyx chinensis (Nees) Bremek.) (GenBank accession no. AY489384) and Sericocalyx crispus (L.) Bremek. (AY489383) respectively in the DNA database, supporting that the new species is genetically closely related to the Sericocalyx group. Strobilanthes namkadingensis is distinguished from S. chinensis by having more secondary veins of lamina (6–8 pairs vs. 5 pairs), longer spikes (3.5–10 cm long as opposed to S. chinensis up to 3 cm long), and 4–6 seeds per capsule (vs. 8-seeds).