Lithocarpus orbicarpus Strijk, 2014

Strijk, Joeri S., Sirimongkol, Sukontip, Rueangruea, Sukid, Ritphet, Nikom & Chamchumroon, Voradol, 2014, Lithocarpus orbicarpus (Fagaceae), a new species of Stone Oak from Phang Nga province, Thailand, PhytoKeys 34, pp. 33-45 : 34-38

Lithocarpus orbicarpus Strijk sp. nov. Fig. 1 , 2

Type.

THAILAND, Ton Pariwat Wildlife Sanctuary, Mueang district, Phang Nga Province, 8°37'25"N; 98°33'14"E; alt. 455 m, 16 July 2013, Chamchumroon et al. 5823 (Holotype: BKF; Isotypes: E, K, L, SING).

Diagnosis.

Lithocarpus orbicarpus is a small-medium sized tree. It differs from similar species by its unique orbicular acorns, each covered with a dense pattern of irregularly placed scales, which completely conceal the nut, except for a tiny apical pore, and which are arranged in a dense cluster on an erect woody spike. Unique for Thai species of Lithocarpus , almost the entire surface of the round nut is covered with scar area (re ceptacle tissue), leaving only the topmost part of the nut covered with a thin vestigial exocarp layer. Pending discovery of additional individuals, the species appears to be locally restricted to low-mid-elevation forests in the peninsular region of Thailand.

Description.

Small-medium sized tree, up to 15 m tall. Bark smooth to slightly rough grey-green, with superficial horizontal lines. Sapwood white to yellow, with inner bark ridges forming light brown longitudinal slits in sapwood surface. Branches dark brown to grey brown, mostly glabrous, densely lenticellate; young twigs, leaf buds and old fruits with short, soft (occasionally long) gray indumentum. Leaf buds tiny and terminal buds solitary. Leaves simple; lamina elliptic to oblanceolate with (strongly) acuminate tip, 11.0-22.3 × 4.4-7.1 cm. Margin entire. Leaves often with slightly asymmetric lamina. Leaf apex acuminate to strongly acuminate, leaf base cuneate to slightly attenuate. Both surfaces generally glabrous except emerging leaf buds, terminal shoots and young leaves, which have soft grey indumentum. Young leaves light green, but turning dark green above and glaucous below when older. Venation. Pinnately veined; secondary venation discretely anastomosing near the leaf margin. Pairs of secondary veins 9-13, slightly raised and clearly visible on underside of leaf. Peduncles carrying fruits 5-11 cm long, up to 1 cm thick at the base, glabrescent, grey-brown and densely lenticellate. Male and female inflorescences not seen. Infructescence a woody spike, terminal, up to 15-21 cm long. Fruits sessile on thick woody peduncle, closely pressed against each other, but walls of individual units not fused. Number of fruits per infructescence very variable, ranging from 9-20 units. Acorn. Orbicular, globose, 2.7-3.4 by 2.9-3.5 cm (including cupule) and covered with glabrous, semi-concentric interlocking ridges when young, which transform over time into ridges with irregularly placed scales. Cupule nearly completely enclosing the nut, indehiscent, but showing small cracks when mature; fruit wall up to 4-6 mm thick, apical pore very small, 1-4 mm wide, exposing the persistent punctiform styles (3) and a tiny fraction of vestigial exocarp. Young cupule walls light green, ridges light to dark brown. Old cupule walls turning light brown to yellow-brown and pubescent with short (occasionally long), greyish-yellow indumentum. Nut 1 in each cupule, ball shaped, globose, 2.4-2.9 by 2.6-3.0 cm. Up to 95% of surface area of the nut made up of scar area (receptacle tissue), upper 5% of surface area of the nut slightly raised and made up of vestigial exocarp layer. Nut scar pale yellow-whitish, tiny exocarp layer light brown. Scar area covered with deep groves and red-brown to purplish vein-like lines, stretching down to the base of the nut. Up to 5/6 of the scar area of the young nut (from the base upward) covered with dotted pattern of small depressions. Cotyledons black when dried.

Flowering and fruiting.

Flowering unknown, but thought to be around November-January. Infructescences on the ground in July, fruiting commencing possibly as early as April-May.

Distribution.

This species is only known from Thailand, and has not been recorded outside Ton Pariwat Wildlife Sanctuary, Mueang district, Phang Nga Province. During our field survey, we found only one individual tree, located on a gentle sloping section of closed dense forest. Additional survey work will have to be undertaken to determine the actual population size of this species within the wildlife sanctuary.

Ecology.

This species grows in dense hillside forest at an elevation of around 450 m.

Vernacular name.

Unknown.

Etymology.

Lithocarpus orbicarpus is named after its unique orbicular acorns, arranged densely clustered on an erect spike, of which the cup almost completely encloses the nut (except for a tiny apical pore). The exterior of the cup is covered with a dense pattern of ridges, transforming with age into horizontal and vertical lines with irregularly placed scales. Apart for a tiny portion of the umbo which is covered with vestigial exocarp, the exterior surface of the nut is completely covered by scar. Although the cupule nearly completely covers the nut, the latter is free and not fused to the wall of the cupule - a condition which occurs throughout the genus ( Cannon 2001; Cannon and Manos 2001). Upon drying, the shrinking of the cotyledons inside the nut causes the whole infructescence to make a rattling sound when shaken.

Discussion.

Thailand has a total of 121 species, 2 subspecies and 2 varieties of Fagaceae in four genera indigenous to the country. Of these, nine species ( Castanopsis : 4; Quercus : 1; Lithocarpus : 4) and 1 subspecies ( Quercus : 1) are national endemics ( Bunpha et al. 2011; Phengklai 2008). Three of the endemic Lithocarpus species (including Lithocarpus orbicarpus ) are restricted to small ranges in the peninsular region. Of the 58 Lithocarpus known to occur in Thailand (including this newly described species), 43 species (74%) can be found in the Peninsular floristic province making it the most diverse floristic region (in terms of Lithocarpus species) followed by the North (25 species - 43%). While the Northern (and North-eastern) floristic province is characterized by species that reach high elevation habitat (>75% can be found between 1200-2500 m), the Peninsular complement includes species that are restricted to lower elevations (21 species restricted <500 m asl). With two exceptions ( Lithocarpus falconeri (Kurz) Rehder and Lithocarpus erythrocarpus (Ridl.) A.Camus), none of these species are shared with the North (or North-east). In contrast, four of the Peninsular lowland species ( Lithocarpus lucidus (Roxb.) Rehder; Lithocarpus maingayi (Benth.) Rehder; Lithocarpus reinwardtii (Korth.) A.Camus; Lithocarpus tubulosus (Hickel & A.Camus) A.Camus) are shared with the South-eastern floristic province, in addition to Lithocarpus elephantum (Hance) A.Camus and Lithocarpus pierrei (Hickel & A.Camus) A.Camus, which can only be found in the South-eastern region.

Lithocarpus in Thailand can be further characterized based on their acorn (cupule+nut) properties. The open- or semi-open type, in which the cupule shape ranges from saucer shaped-flat to covering up to 4/5th of the nut is present in 37 species (64%), while the remaining 18 species have cupules that entirely cover the nut, in most cases leaving a tiny portion of the umbo uncovered. With one exception ( Lithocarpus truncates (King ex Hook.f.) Rehder), all closed-type species occur in the Peninsula, and eight are restricted to it (two shared with the Southeast). Lithocarpus orbicarpus resembles species in this group, with its indehiscent and near-closed cupules, restricted geographical distribution and presence in lower elevation habitat, but is clearly distinct from them based on the structure and shape of the fruit, the infructescence and the properties of the nut.

During our field survey, we encountered and collected additional Fagaceae species, e.g. Lithocarpus reinwardtii (Korth.) A.Camus (Burma, Cambodia, Malaysia, Indonesia), Lithocarpus sundaicus (Blume) Rehder (Malaysia, Indonesia, Brunei), Lithocarpus cantleyanus (King ex Hook.f.) Rehder (Burma, Malaysia, Singapore) and several, as of yet, unidentified collections. Additional species encountered in previous surveys in the wildlife sanctuary are: Castanopsis javanica (Blume) A.DC. (Vietnam, Malaysia, Singapore, Indonesia); Castanopsis nephelioides King ex Hook. f. (Malaysia, Singapore); Castanopsis purpurea Barnett (Thailand (endemic)); Castanopsis wallichii King ex Hook. f. (Malaysia, Singapore, Indonesia); Castanopsis inermis (Lindl.) Benth. & Hook. f. (Burma, Malaysia, Singapore, Indonesia, Philippines); Lithocarpus bennettii (Miq.) Rehder (Malaysia, Singapore, Indonesia); Lithocarpus clementianus (King) A.Camus (Malaysia, Indonesia); Lithocarpus eucalyptifolia (Hickel et A.Camus) A.Camus (Burma, Vietnam, Cambodia); Lithocarpus falconeri (Kurz) Rehder (Burma, Malaysia); Lithocarpus garrettianus (Craib) A.Camus (China, Burma, Laos, Vietnam); Lithocarpus lucidus (Roxb.) Rehder (India, Malaysia, Singapore, Indonesia, Brunei); Lithocarpus macphailii (Henders.) Barnett (Malaysia, Indonesia); Lithocarpus wrayi (King) A.Camus (Vietnam, Malaysia, Indonesia) and Quercus oidocarpa Korth. (Burma, Vietnam, Malaysia, Indonesia). Out of these 17 species, at least 14 have a geographic distribution that is primarily or completely located in the Sundaland biogeographic region. Conversely, only three species have a distribution that is mostly or entirely contained within the Indochinese biogeographic region. Despite the paucity of detailed biological records on this remote area, the distributional data shows us that the Fagaceae flora in Ton Pariwat Wildlife Sanctuary is distinctly Sundaic in composition, and differs substantially from forests in the more northern Indochinese region. This is in fact not surprising, as the Ton Pariwat Wildlife Sanctuary is located near the southern edge of one of the world’s major phytogeographic and zoogeographic transition zones: the ~500km stretch between the biogeographically distinct and well-known Isthmus of Kra - the narrowest part of the connection between mainland Southeast Asia and the Malay Peninsula (10°30'N) - and the line between Kangar (Malaysia) - 6.°51'N, and Pattani (Thailand) 6°87'N. Within this relatively short distance, an abrupt and major shift takes place from northern Indochinese flora and fauna, to those distinct for the southern Sundaland region ( Hughes et al. 2003; Meijaard 2009; Parnell 2013; Van Steenis 1950; Woodruff 2003; Woodruff and Turner 2009).

When looking at the Fagaceae flora in the wider region, some properties of Lithocarpus orbicarpus resemble species in Peninsular Malaysia, such as Castanopsis nephelioides King ex Hook.f., but can easily be distinguished from species within Castanopsis (D.Don) Spach, based on the presence of bark ridges that penetrate the sapwood, the nut which is not fused to the cup and the orbicular shape of the fruit. Congeneric species from the Indo-Chinese zone that share some characters with Lithocarpus orbicarpus are Lithocarpus rouletii (Hickel & A.Camus) A.Camus (but fruit with basal scar, flattened, dehiscent; South Vietnam); Lithocarpus pachycarpus (Hickel & A.Camus) A.Camus (but leaves with yellow indumentum, cupules pear-shaped, acorns not orbicular; Vietnam-Laos); Lithocarpus kontumensis A.Camus (but cupules truncate, higher than acorn, cupules sometimes fused; Vietnam-Laos); Lithocarpus lepidocarpus (Hayata) Hayata (but cupules truncate, sometimes fused, fruit not orbicular; central and south Taiwan); and Lithocarpus laoticus (Hickel & A.Camus) A.Camus (but cupule ovoid, high elevation habitat (Tibet, south and central China, Vietnam) ( Wu et al. 1999). Within Thailand, Lithocarpus orbicarpus is unique in its combination of properties, and we outline some of the defining differences with Thai species in Table 1 below.

This species is endemic to Thailand and is currently only known from one location in Ton Pariwat Wildlife Sanctuary. The sanctuary covers a region of low-lying forested mountains with a total area of approximately 100,000 ha at the southern end of the Phuket mountain range. As such it is an integrated part of the Southern Forest Complex of Thailand. The sanctuary is popular for its rich bird- and wildlife (e.g. Blue-banded Kingfisher ( Alcedo euryzona Temminck, Alcedinidae ) and Whitehanded Gibbons ( Hylobates lar L., Hylobatidae ) as well as rare flora, such as Rafflesia kerrii Meijer ( Rafflesiaceae ). Its unique species composition, high diversity and relatively intact forest structure underscore the importance of strengthening ongoing and future conservation measures at Ton Pariwat Wildlife Sanctuary, as a key element of wider conservation efforts in southern Thailand.

Figures

Figure 1. Lithocarpus orbicarpus Strijk, sp. nov. Chamchumroon et al. 5823 (BKF). Technical illustration. A Habit B Detail of glabrous young fruit with ridges and apical pore C Detail of interior of young fruit, showing nearly complete fruit scar, covered umbo and ' pitted pattern'; on the nut surface D Infructescence with ripe fruits showing highly irregular scaly patterns on the fruit exterior E Details of seed, from left to right: bottom view, side view, top view. Note venation and crevice pattern on surface of fruit, and cover of the umbo section. All drawings by J. S. Strijk.

Figure 2. Lithocarpus orbicarpus Strijk, sp. nov. Chamchumroon et al. 5823 (BKF). Pictures from field collection. A Branch with leaves B Young infructescences C Bark and sapwood D Fresh fruit - top view E Fresh fruit - side view F Fresh fruit - bottom view G Dried fruit - top view H Dried fruit - side view J Dried fruit - bottom view (G-J: blue lines demarcate vestigial exocarp; red lines demarcate scar area (receptacle tissue )) K Dried infructescence L Young acorn, opened up to show dotted pattern of small depressions and surface structure of the umbo M Cross-section of fried nut, showing seed coat and black cotyledons N Terminal leaf, twig and very small terminal bud, showing grey indumentum O Young emerging leaf with soft grey indumentum. All pictures by S. Sirimongkol and J. S. Strijk.