Strobilanthes sripadensis Nilanthi, Gopallawa & Jayawardana, 2023

Nilanthi, Rajapakse Mudiyanselage Renuka, Gopallawa, Bhathiya, Jayawardana, Nuwan & Jayasinghe, Himesh Dilruwan, 2023, Strobilanthes sripadensis a new species of Acanthaceae from Sri Lanka, Phytotaxa 592 (2), pp. 127-134 : 128-131

Strobilanthes sripadensis Nilanthi, Gopallawa & Jayawardana sp. nov. ( Figure 2 & 3 )

Type:— SRI LANKA. Sabaragamuwa Province: Ratnapura District, Peak Wilderness Nature Reserve, Katukithula , 6.8038174 N & 80.4681832 E, 1130 m, 11 December 2021, Nilanthi, Gopallawa, Jayawardana & Jayasinghe RMRN119 (holotype PDA!) .

Diagnosis:— The new species resembles S. pentandra , but differs by having leaf apex short acuminate (vs. acute), margin entire or slightly sinuate (vs. serrulate), lateral veins 5–7 pairs (vs. 4–5), outermost bract longer than the inner one (vs. outermost smaller than the inner), bract, bracteole, and calyx pubescent (vs. glabrous), corolla white with prominent dark purple lines at throat (vs. pale violet), fertile stamens 4 (vs. fertile stamens 5).

Description:— Subshrub, slender, up to 50 cm high. Stems terete, glabrous, woody, slightly swollen at node, transverse ridges not prominent. Leaves opposite, unequal in each pair; petioles 1.4–2.5 cm long, glabrous; blades oblong to elliptical, 6.2–10.5 × 2.1–3.6 cm, base cuneate, margin entire or slightly sinuate, apex obtusely short acuminate, adaxially dark green, glabrous with numerous cystoliths, abaxially paler green, glabrescent, venation camptodromous, lateral veins 5–7 pairs, prominent on both surfaces, tertiary veins inconspicuous. Inflorescences of bracteate heads, terminal or axillary opposite pairs on short leafy branchlets; heads oblong, few-flowered, 1.3–5.1 × 1.1–1.9 cm, glabrous; peduncles 1.8–4.7 cm long; flowers sessile; rachis glabrescent. Bracts broadly oblong, 0.5–1.0 × 0.2–0.6 cm, apex obtuse, slightly concave, the outermost ones longer than the inner ones, pubescent on adaxial surface and margin towards the apex, then densely glandular pubescent on mature capsule. Bracteoles linear-oblong, 7.9–9.1 × 1.9–2.0 mm, apex obtuse, pubescent along margin towards the apex, then glandular-pubescent. Calyx five-lobed to about half of the length; lobes linear, 8.9–9.0 × 1.9–3.0 mm, apex acute, margin pubescent towards the apex, then densely glandular-pubescent when fruiting, persistent. Corolla 1.4–1.5 cm long, white with prominent dark purple lines at throat, outside glabrous, inside glabrous except at the place of the insertion of the stamens, tube very narrowly cylindrical for 1.3–1.4 cm, then abruptly inflated and campanulate, flower diameter 2.1–2.3 cm, lobes obovate, 10–13 × 4–8 mm, spreading. Stamens 4, exserted, didynamous; filaments glabrous except for a few hairs at the base, shorter pair 12.9–13.1 mm long, longer pair 18.2–19.0 mm long; anthers bithecous, subsagittate, dorsifixed near to the base, anthers yellow brown. Staminode 1. Ovary two locular, oblong-elliptic, 2.5–3.0 mm long; style exserted, slightly curved, 1.7–2.0 cm long, glabrous; stigma unlobed. Capsule 8–9 mm long, 2–3 mm wide, narrowly oblong-ellipsoid, glabrous, 4-seeded. Seeds, ca. 1.5 mm broad softly pubescent.

Pollen Morphology:— Pollen grains of S. sripadensis ( Figure 4 ) are spheroidal, 47–56 × 2.7–2.9 µm, 3-colporate, equatorial. Carine and Scotland (1998) observed the pollen morphology of 25 Strobilanthes species from Sri Lanka. They recognized 13 ellipsoid pollen types and 12 spheroidal pollen types for Sri Lankan Strobilanthes species. Pollen morphological characters showed a great variability among Sri Lankan Strobilanthes species.

Etymology:— This specific epithet “ sripadensis ” refers to the type locality of this species where the term “ Sri Pada” means “holy footprint” in Sinhala and comes from an indentation at the top of the mountain of the same name which is believed by Buddhists to be the foot print of lord “Gauthama Buddha”. This mountain, which is revered by Sri Lanka’s four main religions, is located within the Peak Wilderness Nature Reserve in close proximity to the type locality.

Phenology:— Flowering in December and fruiting in February.

Distribution and Habitat:— The new species is currently known only from Katukithula and Warnagla in Peak Wilderness Nature Reserve ( Figure 1 ). It grows in the wet zone, in the transitional gradient between lowland rainforest and sub-montane forest at an elevation of 1130 m. This species inhabits areas along the nature trail appearing to prefer well-shaded areas of higher forest cover. Associated species are Syzygium alubo Kosterm (1981: 34) , Garcinia echinocarpa Thwaites (1854: 71) and Aporosa fusiformis Thwaites (1861: 288) .

Additional specimens examined (paratypes):— SRI LANKA. RATNAPURA DISTRICT: Peak Wilderness Nature Reserve , Katukithula, 6.8038174 N & 80.4681832 E, 1130 m, 11 December 2021, Nilanthi, Gopallawa, Jayawardana & Jayasinghe BGAPK001 ( PDA) ; same locality, same date, Nilanthi, Gopallawa, Jayawardana & Jayasinghe BGAPK002 ( PDA) ; same locality, same date, Nilanthi, Gopallawa, Jayawardana & Jayasinghe BGAPK003 ( PDA) .

Conservation status:— About 20 individuals were observed at, Katukithula with the extent of occurrence ca. 0.25 km 2. and about 25 individuals were observed at Warnagala with the extent of occurrence ca. 0.25 km 2 This newly described species may be facing the threat of extinction in the wild due to the low number of plants representing the entire known populations and its limited distribution. Between 2018 and 2021, it is shown that Katukithula population has a significant decline, with a loss of approximately 80% of the population. Furthermore, due to its presence along the edge of a path, there is a threat to this population from road clearing and weeding. Therefore, this new species is assigned to the category ‘Critically Endangered’ (CR) in accordance with the International Union for Conservation of Nature guidelines ( IUCN, 2019). Further field investigations are required to determine if other populations of S. sripadensis are present.

Note:— A detailed comparison between the new species and S. pentandra is given in Table 1 .

Figures

FIGURE 1. Type localities of Strobilanthes sripadensis and Strobilanthes pentandra in Sri Lanka.

FIGURE 2. Strobilanthes sripadensis. A. Floweringbranch;B.Leaf; C.Close up of the leaf surfacesadaxial andabaxial;D. Inflorescence; E. Bract; F. Bracteole; G. Calyx; H. Corolla split open showing stamens and anthers; I. Capsule; J. Glandular hairs on bracts at fruiting. K. Seed (Drawn by Rukmal Ratnayake based on the holotype).

FIGURE 3. Strobilanthes sripadensis. A. Flowering branch; B. Abaxial surface of a leaf; C. Inflorescence; D. Front view of the corolla; E. Bracts (adaxial and abaxial); F. Bracteole; G. Calyx and Style; H. Corolla opened showing stamens and anthers; I. Stamens; J. Capsule; K. Seeds; L. Glandular hairs at fruiting.

FIGURE 4. Pollen grains of Strobilanthes sripadensis A, B: Polar view. C: Spines (spine height marked). D: Spines (spine width marked).