Dendrobium taprobanium Atthanagoda, Priyadarshana, Wijewardhane, Aberathna, Peabotuwage & Kumar, 2020

Priyadarshana, Tharaka Sudesh, Atthanagoda, Anusha Gayan, Wijewardhane, Ishara Harshajith, Aberathna, Nimantha, Peabotuwage, Indika & Kumar, Pankaj, 2020, Dendrobium taprobanium (Orchidaceae): a new species from Sri Lanka with taxonomic notes on some species of the genus, Phytotaxa 432 (1), pp. 81-94 : 82-83

publication ID	https://doi.org/ 10.11646/phytotaxa.432.1.7
persistent identifier	https://treatment.plazi.org/id/345E404C-FFEE-FFFB-6CB3-FB92FCD43E98
treatment provided by	Felipe
scientific name	Dendrobium taprobanium Atthanagoda, Priyadarshana, Wijewardhane, Aberathna, Peabotuwage & Kumar
status	sp. nov.

Treatment

Dendrobium taprobanium Atthanagoda, Priyadarshana, Wijewardhane, Aberathna, Peabotuwage & Kumar View in CoL ,

sp. nov. Section: Stachyobium . ( Figs. 1 View FIGURE 1 ; 2 View FIGURE 2 & 3E, F View FIGURE 3 ).

Type:— SRI LANKA, Kithulgala: Makandawa Forest Reserve, Parawalathanna, Kegalle district, Sabaragamuwa Province, 185 m, 28 Oct. 2005, Atthanagoda AKAG 01 (Holotype: PDA!).

Diagnosis:— D. taprobanium sp. nov. shows close morphological affinity to D. panduratum from Sri Lanka and southern India , and D. trinervium from Indochina. However, D. panduratum has pinkish-white flowers and a panduriform lip, which bears a thickened glabrous callus that runs from the posterior end of the lip and terminates before the tip of the midlobe. D. trinervium has greenish-white flowers, and its obovate lip has three rows of thickened glabrous calli arising from the middle or posterior end of the lip and extending to the apex of the midlobe. In contrast, D. taprobanium has greenish-white flowers, and its lip bears a rounded callus with fine glandular hairs at the seam of the hypochile and epichile.

Description:— Epiphytic or lithophytic herbs with tufted pendent stems bearing filiform roots at the base. Pseudobulbs clumped together, ovoid with tapering ends, 3.0– 4.5 cm long, 1.0– 1.5 cm wide, internodes covered with sheathing leaf bases. Leaves 3 or 4, linear-oblong or lanceolate, 2.5–5.5 cm long, 1.5–1.9 cm wide, distichous, sessile, acute to acuminate, conduplicate, slightly twisted at the base then spreading into thin sheath covering the stem internode. Inflorescence pendulous, lateral or terminal, 1.5 cm long, green, bearing 2–4 flowers. Floral bracts minute, ovate, ca. 1.0–2.0 mm, obtuse. Flowers light-green with greenish-white tinge on the petals and sepals, and a bright-green throat at the lip base running down to the mentum, ca. 1.5 × 1.4 cm. Sepals and petals dissimilar, petals slightly smaller than sepals. Dorsal sepal oblong-lanceolate, 0.80 × 0.35 cm, acuminate, midrib bright-green. Lateral sepals falcately ovate, ca. 0.7 × 0.4 cm, broad at base, lanceolate, acuminate, midrib bright-green. Petals oblanceolate to linear-lanceolate, ca. 0.7 × 0.3 cm, acute, midrib bright-green. Lip obovate, ca. 0.7 long, 0.5 cm and 0.2 cm wide respectively at the epichile and hypochile, 3-lobed with a circular green callus at the seam of epichile and hypochile. Lateral lobes smaller than midlobe, ca. 0.25 cm long, laterally curled over the column and distally bent outwards, acute. Midlobe flat, succulent, broadly obovate, ca. 0.8 cm long, 0.2 cm, 0.35 cm and 0.5 cm wide respectively at the base, middle and apex, margin crenulate, base bright-green in colour. Column short, ca. 2.0 mm long, base elongated into a stout mentum, mentum 0.6–0.7 mm long, spur-like, slightly curved, 2-lobed at the apex. Anther terminal, 2- lobed. Operculum broad, ca. 0.2 × 0.2 cm. Pollinia 4, green, waxy, in two pairs, clavate, ca. 0.3 × 0.15 cm. Mature fruit bright-green, ca. 1.4 × 0.9 cm.

Flowering:— August to December.

Specimens examined:— SRI LANKA, Kithulgala: Makandawa Forest Reserve, Parawalathanna, Kegalle district, Sabaragamuwa Province, 185 m, 28 Oct. 2005, Atthanagoda AKAG 04 (PDA-isotype).

Habitat and ecology:— D. taprobanium is found only in Makandawa Forest Reserve, Sabaragamuwa Province, Kegalle district, Kitulgala, Parawalathanna, Sri Lanka __ a lowland-wet zone forest ( Ashton et al. 1997). It grows as an epiphyte or lithophyte on lichen- and moss-covered tree trunks or wet rocks and boulders, under shade. Host trees observed are Shorea zeylanica (Thwaites) Ashton (1973: 363) ( Dipterocarpaceae ), Schumacheria castaneifolia Vahl (1810: 122) ( Dilleniaceae ), Dillenia retusa Thunberg (1791: 200) ( Dilleniaceae ), Barringtonia racemosa (L.) Sprengel (1826: 127) ( Lecythidaceae ) and Vitex altissima Linné (1782: 294) ( Lamiaceae ). Plants of D. taprobanium were observed at 3.5 m to 5.0 m height from the ground level. Other orchids, D. maccarthiae and D. panduratum were also observed in the close vicinity.

Conservation status:— At present, D. taprobanium is only known from a single location at Makandawa Forest Reserve, Parawalathanna, Kitulgala, Kegalle District, Sabaragamuwa Province in the wet-zone of Sri Lanka. Area of Occurrence was 4 km 2 as estimated by the Geospatial Conservation Assessment Tool (GeoCAT, see Moat 2007). Based on our field surveys, between 2005 to 2018, the total number of mature plants at the type locality decreased from 120 individuals to 100 in 2016 and further down to 90 individuals in 2018. Despite the fact that the type locality is inside a protected area, deforestation was found be the major threat due to road construction activities. Illegal collecting for horticultural purpose is also found to be a threat. D. taprobanium seems very specific to its microhabitat and it grows under ~60–90% of canopy cover.

Based on the IUCN guidelines, with a population of less than 200 mature individuals, ~30% of population decline within a period of 13 years, and threats due to habitat degradation as well as illegal collection, D. taprobanium can be assessed as Endangered (EN) (B2ab(iii,iv,v)c(iii,iv); C2a(i); D) ( IUCN 2019).

Etymology:— The species epithet taprobanium is derived from ‘ Taprobane ’, the historical name for Sri Lanka given by the ancient Greeks. This Greek word however, is derived from a historical Sinhalese name of Sri Lanka, i.e., “ ” (translated as Kingdom of Tambapanni), and this Sinhalese name is derived from Sanskrit (an ancient language of India ), “ Tambraparni ” (tambra -copper, parni -leaf). The name “ Tambraparni”, was given by the Prince Vijaya (the first King of Sri Lanka) referring to the red colour of the soil (due to high Copper content) that made the island looks like a copper-coloured leaf floating on water.