Rhododendron rawatii I. D. Rai & B. S. Adhikari, 2012

Rai, Ishwari Datt & Adhikari, Bhupendra Singh, 2012, Rhododendron rawatii (Ericaceae), a new species from the Western Himalaya, India, Phytotaxa 71 (1), pp. 10-16 : 12-15

Rhododendron rawatii I. D. Rai & B. S. Adhikari , sp. nov. ( Figs. 1 & 2 )

Rhododendron rawatii resembles R. fulgens Hooker (1851 : t. 25) in habit and having peeling bark, glabrous young shoots and shining mature leaves but differs in the abaxial surface of leaves with fascicled cottony hairs in between the lateral veins, a bright pink, not shiny corolla and a large globose calyx with hairy margins.

Type:— INDIA. Uttarakhand: Kedarnath Wildlife Sanctuary, Tungnath , along timberline ecotone, 30°30'8.00"N, 79°13'27.61"E, 3320 m, 20 April 2010, I . D. Rai 11451 (holotype WII!) .

Shrub to small tree up to 4.5 m tall; bark thin, papery, peeling, reddish–white. Leaves mostly clustering at the ends of branches; petiole glabrous, 15–25 mm long; lamina infolded towards abaxial side from margins at maturity, becoming more convex towards adaxial surface, 122–196 × 46–79 mm, leathery, elliptic to ellipticoblong, base rounded to cordate, apex mucronate, margin entire; adaxial surface green and shiny, abaxial surface with sparsely distributed fascicled white to brown cottony hairs in between lateral veins, becoming more or less glabrous at maturity (1 year); veins conspicuous, lateral veins in 30–44 pairs. Inflorescence terminal, rachis 13–20 mm long, flowers 13–16, loosely arranged; pedicel glabrous, 6–13 mm long; bracts elliptical, convex adaxial surface, apex cuspidate; bracteoles 2, hairy; sepals 5, 2.1–5.6 × 2.7–4.6 mm, membranous, globose, pink, margins ciliate with weak hairs; petals 5, tube open-campanulate, 37–49 × 47–59 mm (tube length × width at throat), bright pink, not shiny, glabrous, notched, margins entire, with dark pink to brown spots in the corolla tube, well-marked nectar pouches at base of each petal; stamens 10, unequal, 9–19 to 21–32 mm long (smallest and longest), filaments pubescent at base, white; ovary cylindric, glabrous, green, 5–7 mm long at the time of flowering; style glabrous, 24–28 mm long, slightly shorter than the corolla tube, persistent; stigma capitate, green, 5-lobed. Capsule 17–28 × 5–7 mm, slightly curved at maturity, glabrous, dehiscing from the tip of capsule, placenta remaining attached to central axis after dehiscence; seeds numerous and minute, 1.5–2.5 × 0.3–0.5 mm, tailed, tail up to 0.25 mm, compressed and brown in colour.

Etymology: —The epithet rawatii acknowledges Prof. Gopal Singh Rawat, one of the leading phytotaxonomists and ecologists of India.

Phenology: —The flowering period lasts from March to mid-May and capsule dehiscence starts from October onwards.

Comparison: —The new species resembles R. fulgens and shares several common characters, such as habit (a small tree to shrub), peeling bark, glabrous young shoots and shining leaves at maturity. The new species differs in many characters as follows: light green abaxial surface of leaf with fascicled cottony hairs in between lateral veins in R. rawatii , whereas in R. fulgens the indumentum wholly obliterates the venation. Flowers are dark pink having a globose calyx with hairy margins in R. rawatii , whereas in R. fulgens petals are bright blood-red, highly polished and shining, the calyx is minute.

Study area, forest type and climate: —The study area is located in the state of Uttarakhand of the Indian Republic ( Fig. 3 ). The species is mainly recorded in the subalpine–timberline ecotone region. The subalpine forests are dominated by Quercus semecarpifolia Sm. , Betula utilis D. Don , Abies spectabilis (D. Don) Mirb. and Rhododendron arboreum with krummholz dominated by Rhododendron campanulatum Don (1821: 410) . Six species of Rhododendron , viz. R. arboreum , R. barbatum Wallich ex Don (1834: 844) , R. campanulatum , R. anthopogon Don (1821: 409) , R. lepidotum Wallich ex Don (1834: 845) and R. nivale Hooker (1851: 26 b) have been reported from the Western Himalaya. The climatic data were recorded for 3 years during 2008–2010 at Tungnath area (3300 m a.s.l.) in Kedarnath WS (type locality), and the climate of the region has three prominent seasons: long winter (October to April), short dry summer (May to June) and rainy season (July to September). The mean annual temperature ranged between -8.9°C (January) and +25.6°C (May) with an annual average of 6.6±0.7°C. The annual precipitation was 2410± 432 mm, of which 89% was received during June–September. The area remains snow-bound for 85±28 days per year ( Adhikari et al. 2011).

Distribution and Habitat: —The new species is described from the type locality inside the Kedarnath Wildlife Sanctuary along the timberline zone. Another population is recorded enroute to Chhipla-Kedar from Chhirkila (29°57'26"N, 80°30'55"E, 3120 m) in Pithoragarh district, Uttarakhand (ca. 150 individuals). Individuals were found to grow at the edge of open canopy forest in northwest aspects between 3100 and 3375 m. The daily mean air temperature remains below 0°C for more than 3 months, and the soil remains under snow for about 3–4 months in a year and acidic in nature (pH 4.3–5.0).

Phytogeography, endemism and conservation status: —The species has so far been recorded from only two localities in the Western Himalaya. A regenerating population of about 11 individuals was located in Tungnath area of Kedarnath Wildlife Sanctuary and ca. 150 individuals were found in Pithoragarh district. The distribution of species is very narrow, and plants were found near and above 3100 m elevation along the subalpine–timberline zone. According to IUCN criteria, the species falls under the Endangered (EN) category ( IUCN 2011, section 2.3) having very small (<250 individuals) and restricted populations. On the basis of total number of individuals (ca. 161 individuals) found in 2 populations, the status of species may be considered for immediate conservation measures and the habitat as critical, as the area is under high anthropogenic pressure. The geographical range is extremely narrow and the population is fragmented, therefore, the species requires immediate in-situ conservation and habitat management interventions.

Figures

FIGURE 1. Rhododendron rawatii I. D. Rai & B. S. Adhikari sp. nov. A. & B. Habit and habitat (flowering and vegetative stage). C.Leaf abaxial and adaxial surface. D. & E. Bark. F. Inflorescence. G. Flower. H. Stamen, calyx and bract. I. Basal part of the flower with calyx. J. Ovary, calyx and bracteoles. K. Flower bud. L. Leaf bud. M. & N. Mature and dehisced capsule. O. Seeds. (Photographs by IDR from type locality).

FIGURE 2. Rhododendron rawatii I. D. Rai & B. S. Adhikari sp. nov. A. Flowering branch. B. Leaf: adaxial (left) and abaxial (right) surface. C. Flower with bracteoles. D. Androecium and gynoecium. E. Bract. F. Intact and dehisced capsules. G. Seeds (Illustration by IDR from type locality).

FIGURE 3. Map of India (left lower side) and Uttarakhand state (representing locations of the habitat of R. rawatii recorded (left star type locality at Tungnath in Kedarnath Wildlife Sanctuary, Rudraprayag (R) district and right star enroute Chhipla–Kedar in Pithoragarh (P) district).