Mountains of eastern Indochina form a series of highlands known today as the Truong Son or Annamese Range. This range stretches as a southeastern extension of the Himalayas for more than 1000 km from the highlands of Yunnan across the entire peninsular territory to the seashore of southern Cambodia. During the long geological history of the region these mountain chains, running in a longitudinal direction, created a corridor for repeated plant migrations from subtropical and temperate Asia to tropical highlands of Indochina. Ancient plant movements and species isolation within numerous mountain peaks resulted in active processes encouraging species formation within Indochina (Averyanov et al., 2003). Isolation of a number of temperate Asian or Holarctic genera led to the creation of endemic and sub-endemic species within the mountain systems of eastern Indochina. Distribution of Pinus within eastern Indochina is a result of these migrations and subsequent isolation within a number of more or less isolated mountain massifs. As a result, eastern Indochina may constitute the region of the world with the highest diversity of Pinus (Farjon, 2001; Hiep, Vidal, 1996; Hiep et al.. 2004; Luu, Thomas, 2004). From 7 to 9 native Pinus species and varieties were inventoried within this territory during recent explorations, observations and taxonomic studies (Businsky, 2013; Phan Ke Loc et al., 2013).
The highlands of southern Vietnam provide a home to Ducampopinus krempfii (Lecomte) A. Chev., a unique relictual endemic within the Chu Yang Sin and Bi Dup Mountains. This peculiar primitive pine is possibly the ancestor of all modern pines (Orlova, Averyanov, 2004). This taxon is sometimes regarded as a monotype subgenus of the genus Pinus (Pinus subgen. of Ducampopinus (A. Chev.) Little et Critchfield. Four well defined allopatric varieties of the endemic Pinus dalatensis Ferré - P. dalatensis var. dalatensis, var. anemophila (Businsky) Aver., var. bidoupensis Businsky and var. procera (Businsky) Aver. inhabit isolated mountain areas within southern and central Vietnam and in Laos. A number of isolated massifs of rocky karstic limestone in northern Vietnam and in adjacent regions of China represent the area of distribution of the subendemic P henryi Masters and four calcium- dependent endemic races of P wangii Hu et W.C. Cheng - P wangii var. wangii, var. kwangtungensis (Tsiang) Silba, var. varifolia (Nan Li et Y.C. Zhang) Aver. and var. eremitana (Businsky) Aver. Two widespread species, Pinus kesiya Gordon and P latteri Mason, occasionally form scattered mixed and coniferous forests throughout Indochina. Meanwhile, many mountainous areas of eastern Indochina, particularly regions along the border with Vietnam remain insufficiently explored because they are often inaccessible. Such areas certainly contain the potential for the discovery of numerous local endemic plants during future scientific explorations. The recent discovery ofthe new 5-leaved pine within the ancient, isolated and highly-eroded sandstone plateau on the border of NE Laos and NW Vietnam is a positive example of this assumption.
This unusual pine was first recognized by Vietnamese geologists at the end of 2011 within the steep cliffs located within the peripheral zone of Pha Luong Mountains and spreading along Laos-Vietnam border between Houaphan and Son La provinces. This remarkable discovery was immediately announced in the January issue of the People’s Army Newspaper widely distributed in Vietnam (Lương Tứ Chấn, 2012) and was also noted in a short scientific article in the Vietnam Environment Administration Magazine (Lê Trần Chấn et al., 2012). In 2012 the discovery of the new species was confirmed and voucher herbarium specimens were collected during field work associated within the Rufford grant program - “Conservation of Conifer Tree Species in Hoa Binh - Son La Limestone Corridor” (Nguyen Duc To Luu, 2013; Phan Văn Thăng et al., 2013). These initial assessments and attempts to understand this newly discovered species resulted in its tentative identification as “Pinus aff. armandii Franchet” (Nguyen Duc To Luu et al., 2013; Phan Ke Loc et al.. 2013). In their publications, however, these authors indicated certain morphological differences found in the Vietnamese pine from P. armandii (Phan Ke Loc et al., 2013). The preliminary identification of the discovered plant as P fenzeliana Hand.-Mazz. was additionally proposed on the basis of speculative studies of plant images available on the Internet (Businský, 2013). Further field and laboratory studies by the authors confirmed the obvious differences between the discovered plant from both P. armandii and P. fenzeliana, the latter known from isolated locations in southern China. Given the clear distinction of the discovered tree and its morphological differences from all known species of the genus, it was described as a new species under the name Pinus cernua L.K. Phan ex Aver., K.S. Nguyen et T.H. Nguyen in Averyanov et al. (2014: 28). A detailed description and preliminary
Assessment of this very rare endangered species is presented below.
Pinus cernua L.K. Phan ex Aver., K.S. Nguyen et TH. Nguyen in Aver. et al., 2014, Nordic J. Bot. 32(6): 792. - P. armandii auct. non Franch.: Nguyen Duc To Luu et al., 2013, Proc. 5th Nat. Sci. Conf. Ecol. Biol. Res. (Hanoi): 152; Phan Văn Thăng et al., 2013, Quide Conif. Hoa Binh, Son La prov.: 20; Phan Ke Loc et al., 2013, Ecol. Econ. J. 45: 42. - p. fenzeliana auct. non Hand.-Mazz.: Businský, 2004, Willdenowia 34: 218; id., 2011, Phyton 51, 1: 84; id., 2013, ibid., 53, 2: 247, 257.
Distribution of Pinus cernua yvJVi - Maximal estimated area of occurrence (less than 74 km2)
------- - Border of Xuan Nha Nature Reserve _ Maximal estimated area of occupancy (less than 25 km2)
------- - Border of buffer zone , . Documented localities (1-12)
Fig. 1. Expected distribution area of Pinus cernua in the area of Pha Luong Mountains.
Green line designates the maximum estimated area of the species occurrence (less than 74 km2); pink shading marks the maximum estimated area of the species occupancy (less than 25 km2); red dots (and appropriate black figures) designate the localities where the species was studied; red and blue lines show the border of Xuan Nha Nature Reserve and the border of its buffer zone, respectively.
Described from the border region of northern Laos and Vietnam (“Laos-Vietnamese border between Son La and Houaphan provinces”).
Type. Vietnam, Son La Province, Van Ho District, Chieng Xuan Municipality, Co Hong village, territory of Xuan Nha Nature Reserve, NE. slopes of Pha Luong Mountains. Primary coniferous forest with Pinus cernua on very steep mountain slopes and cliffs composed of brown sandstone at elev. 1000-1050 m a.s.l., 20°42’14.2’’ N, 104°43’53.9’’ E, 12 November 2013, L. Averyanov et al. CPC 6992 (holo - Herbarium of the Center for Plant Conservation!, iso - LE!). Figs 1, locality 7; 2B; 3-5.
Fig. 2. Habitats and localities of Pinus cernua in Pha Luong Mountains.
A - Typical landscape of the central part of Pha Luong Mountais; B - Mature tree of Pinus cernua in its locus classicus; C-G - studied locations of P cernua: C - locality N° 8, D - locality N° 9, E - locality N° 10, F - locality N° 11, G - locality 12
Tree 20-30(35) m tall, 0.4-0.8(1) m dbh. Canopy conical, becoming with irregularly rounded with age; branches suberect to pendulous; leafy branchlets gray-green, olive or yellow-brown, slightly glaucous, glabrous. Bark dull gray-brown to dark brown, roughly fissured into irregular polygonal flat or slightly concave plates, often resinous, inner bark reddish-brown, finely fibrous. Winter buds, orange-brown, often, cylindric, 1-2 cm long, 3-5 mm in diam.; scales narrowly triangular, (3)4-5 mm long, 1-2 mm wide at the base, acuminate, with slightly recurved scarious apex. Needles in fascicles of 5, (12)15-20(22) cm long, 0.6-0.8 mm thick, rich dark green, slender, cernuous, slightly twisted, serrulate, triangular in cross section, with 25-32 rigid erect denticles per cm along the each edge and with 3-4 stomatal lines on the ventral lateral surfaces; vascular bundle 1, large; resin ducts 3, subequal, medial and two lateral; the sheath early deciduous. Pollen cones numerous, in spiral clusters at the base of new shoots, ovoid, later elongate, suberect, more or less stout, 0.8-1.5 cm long, 6-8 mm in diam. Seed cones on stout peduncles 1-2 cm long, commonly clustering 2-6 in a whorl, rarely alone, erect, later facing in all directions, persistent for many years, brown to dark brown, ovoid, 8-11 cm long, 5-7 cm in diam., dehiscent at maturity, often profusely resinous. Seed scales woody, rigid, obovate-deltoid, 2.4-2.8(3) cm long, 1.5-2.5 cm wide, apophysis deltoid, recurved and thickened at apex in form of transversal finely grooved cushion, umbo insignificant, without mucro. Seeds dark brown, smooth, oblique obovoid, 1-1.2 cm long, 0.5-0.7 mm in diam., with rudimentary scarious thin wing 1-2 mm wide disintegrating to seed maturity and occasionally remaining in form of low irregular distal rim. Pollination February-March, seeds September-October.
Paratypes. Vietnam. Sơn La prov., Chiềng Xuân (N.D. Luu et al. 2013): 4 Dec. 2012, P.V Thăng et al. 5 (VNU, PanNature Herbarium); 13 Dec. 2012, N.Đ.T. Lưu et al. 24 (VNU, PanNature Herbarium); 16 Apr. 2013, P.K. Lộc et al. P 11077; 16 Apr 2013, P 11078-11080; 17 April 2013, P 11081-11082; 18 April 2013, 11084-11089 (LE, VNU, PanNature Herbarium).
Documented photo records. NW Vietnam, border area of Houaphan and Son La Prov., Van Ho Distr., Chieng Xuan Municipality, Co Hong village, territory of Xuan Nha Nature Reserve, Pha Luong Mt., 20°42‘07.5“, N, 104°40‘41.7“ E, 1150 m, 12 Nov. 2013, AveryanovL. et N.S. Khang photos, CPC s.n. (Fig. 2C, locality JV°8 on Fig. 1); 20°41‘39.4“, N 104°39‘22.9“ E, 1400 m, 13 Nov. 2013, N.S. Khang photos, CPC s.n. (Fig. 2D, locality N°9 on Fig. 1); 20°41‘24.7“ N, 104°39‘13.8“ E, 1380 m, 13 Nov.
2013, N.S. Khang photos, CPC s.n. (Fig. 2E, locality tf°10 on Fig. 1); 20°41‘31.0“ N, 104°39‘53.2“ E, 1450 m, 13 Nov. 2013, N.S. Khang photos, CPC s.n. (Fig. 2F, locality M>11 on Fig. 1); 20°41‘47.9“ N, 104°39‘45.6“ E, 1430 m, 13 Nov. 2013, N.S. Khang photos, CPC s.n. (Fig. 2G, locality N°12 on Fig. 1). All photos are deposited at the Center for Plant Conservation and LE Herbarium.
All presently known locations based on published data (Nguyen Duc To Luu et al., 2013) and on original source materials are listed in Table 1 and presented on figs 1 and 2.
Distribution. Endemic of Pha Luong Mountains situated on Laos-Vietnam border between Houaphan and Son La provinces. Hainan?
Table 1. The list of available locations of P. cernuain Pha Luong Mountains presented on figs 1 and 2