Exacum idukkianum Geethakumary, Pandurangan, Ravichandran & Deepu, 2016

Geethakumary, M. P., Pandurangan, A. G., Ravichandran, P. & Deepu, S., 2016, A new species of Exacum (Gentianaceae) from Western Ghats, India, Phytotaxa 282 (3), pp. 225-229 : 226-228

Exacum idukkianum Geethakumary, Pandurangan, Ravichandran & Deepu , sp. nov. ( Fig. 1 )

Type:— INDIA. Kerala, Idukki Distr., Anamudi Shola , 10 o 11 ′ 25.8 ′′ E, 77 o 11 ′ 15.8 ′′ N, 1857 m, 24 September 2012, M. P. Geethakumary 74301 (holotype TBGT 32124 !; isotypes TBGT 32125 !, MH!) .

Perennial herbs, to 2.5 m tall; branched at the upper part of the stem. Stem terete at base, sharply 4-angular above. Leaves subsessile, elliptic to ovate lanceolate, 3–9.5 × 1–2.5 cm, membraneous, glabrous, green, base cuneate to attenuate, margin faintly undulate, apex long acute, (3–)5 veined, veins diverging from base of the lamina with (3–)5 secondary veins on each side of midrib, abaxially prominent. Inflorescence terminal or axillary, dichasial cymes, 3.0– 4.5 × 4.5–5.5 cm; peduncles 2.5–4 cm long; pedicels 1–3 cm long, enlarging in fruit, often drooping. Calyx 5-lobed; tube broadly campanulate, 3–5 × 8–10 mm; lobes narrow, 3–6 cm long, tapering to long point at the apex, truncate to subcordate or in fruit cordate at the base, winged; wings ca. 3 mm broad, accrescent in fruit, with prominent veins. Corolla tube ca. 6 mm long, green; lobes 5, elliptic to broadly elliptic, 2.5–3.5 × 1.2–1.5 cm, apex apiculate, long persistent in fruit but eventually deciduous, deep blue to violet, base yellowish within (at throat) and give star shaped appearance, 3-veined, veins prominent above. Stamens 5, 9–13 mm long; anthers narrowly rectangular, 6–10 mm long, slightly wider at base, slightly curved with the convex back face, base cordate, opening by apical pores that later widen to slits to the base, with a papilla near the apex on the dorsal side; filaments ca. 3 mm long, attached at the throat of the corolla tube. Ovary ovoid, 5–7 mm long; style 1.4–1.8 cm long, curved, stigma capitate. Capsule broadly ovoid, 1–1.3 cm long, dehiscing septicidally, 2-valved; fruiting pedicel ca. 3.5 cm long, drooping; style persistent. Seeds irregularly rhomboid, angular, with shallowly sunken sides.

Phenology:— Flowering and fruiting was observed from August to December.

Etymology:— The specific epithet “ idukkianum ” is derived from the name of the district, “Idukki” where the type locality is situated. Literarily Idukki means, a very narrow gauge between two mountains where the Periyar River, the second largest river in Kerala, passes through, and thus the area becomes a landmark in Western Ghats high ranges.

Distribution and ecology:— This species grows in Shola forest margin at an altitude of 1800–1900 m., in Kerala Province, Western Ghats, India. The associated species include Pteridium aquilinum ( Linnaeus 1753: 1075) Kuhn (1879:11) , Gaultheria fragrantissima Wallich (1820:397) , Rhododendron nilagiricum Zenker (1836:150) , Chionachne gigantea (J. Koenig 1788: 211) Veldkamp (2002: 559) , Garnotia exaristata Gould (1972: 558) , Adenostemma lavenia ( Linnaeus 1753: 902) Kuntze (1891: 304) , Phlebophyllum kunthianum Nees (1832: 83) , Rubus niveus Thunberg (1813: 3) etc.

The type locality, Anamudi Shola, one of the largest shola forest (wet temperate montane forest) ecosystem in the country, co-existing with grassland matrix, has a unique biodiversity and noted for the presence of tree ferns. The area has a high conservation value in terms of biodiversity, geo-morphology, hydrology etc. and the area forms the catchment of several streams, which finally enriches the east flowing river Pambar. By considering its ecological significance, the area has been declared National Park by the State Forest Department and is well protected.

Taxonomic observations:— According to the dichotomous keys and descriptions provided by Klackenberg (1983) the most similar species to Exacum idukkianum is E. wightianum . However, the former can be distinguished from the later [as described and illustrated by Klackenberg (1985) and based on specimen studied] by plants up to 2.5 m tall (vs. up to 1 m tall in E. wightianum ), perennial herbs with terete suffrutescent, woody at base (vs. annual herbs with quadrangular non woody base), subsessile, leaves with 2 secondary veins on each side of midrib, younger ones occasionally with 1 secondary vein on each side (vs. sessile to petiolate, 1–2(–3) secondary veins on each side of midrib), calyx wings accrescent in fruit, with prominent veins (vs. calyx wings accrescent in fruit, without prominent veins), floral guides at corolla throat star-shaped, yellowish-green (vs. floral guides round, yellow), corolla lobes apiculate with prominent veins (vs. acute, without veins), narrowly rectangular, curved anthers, cordate at base (vs. linear, straight anthers, truncate at base) and broadly ovoid capsules (vs. broadly elliptic). A comparative summary of the characters that differentiate these two taxa is presented in Table 1.

Conservation status:—Three populations of this species have been located within the Anamudi Shola National Park at a distance of 2 km from each other in Kerala. Apart from this, based on information from the specimen erroneously identified as E. wightianum at Rapinat Herbarium, Trichy (RHT 14812!), another population is identified at Kodaikanal, Tamil Nadu at a distance of 60 km from the present collection site. According to IUCN criteria ( IUCN 2012a & b, 2013), the extent of occurrence (EOO) between these localities is more than 20 km 2 but within 100 km 2 and there are less than 25 individuals in each population. The area of occupancy (AOO) is less than 0.5 km 2, which indicates its narrow endemic nature. Even though, this species is not prone to disturbances by anthropogenic activities inside the national park, it is prone to wild gracing and evidences are there where the individuals are destroyed by gracing of wild animals and at times destroyed by trampling of elephants as it occurs in Shola margins close to montane grasslands. Therefore, we recommend a preliminary conservation assessment as Critically Endangered [CR B1ac(ii) + 2ac(ii); D].

Discussion:— Exacum wightianum , morphologically similar to E. idukkianum , was also seen in Anamudi shola forest, and our observations suggest that the variation in the magnitude and pattern of floral integration between these two species is not related to the pollinator assemblage. Both species are mainly visited by large bees and floral integration patterns are not likely influenced by the pollinators. Thus, this is not a case of directional selection on individual characters, which may eventually lead to population divergence as suggested by earlier studies ( Armbruster 1985, 1988, Robertson and Wyatt 1990, Galen 1996).

Additional specimens examined (Paratypes):— INDIA. Kerala, Idukki distr., Anamudi Shola , 1855 m, 24 September 2012, M. P. Geethakumary 74358 & 74433 ( TBGT) ; ibid., 1857 m, 22 August 2013, Deepu Sivadas 73659 ( TBGT) ; Tamil Nadu, Madurai distr., Kodaikanal, Pambar Shola , 2100 m, 16 August 1975, K. M. Matthew 14812 ( RHT) .

Figures

FIGURE 1. Exacum idukkianum sp. nov. A. Habit (a. Terete stem, b. Flowering twig), B. Flower (a, b. star shaped, greenish-yellow floral guides), C. Flower bud, D. Calyx split open, E. Corolla split open with stamens and pistil, F. Petal, G. Stamens (g. Papilla), H. Pistil, I. Fruit (from M.P.Geethakumary 74301, photos by S. Deepu)