Thursday, February 13, 2014

[Botany • 2014] Lithocarpus orbicarpus • a new species of Stone Oak (Fagaceae) from Phang Nga province, Peninsular Thailand

Lithocarpus orbicarpus Strijk


A new species is described, Lithocarpus orbicarpus Strijk, collected from Ton Pariwat Wildlife Sanctuary, Mueang district, Phang Nga Province in the Peninsular Floristic Region of Thailand. We provide the first technical illustrations and colour photographs of the new species, as well as a description of its conservation status and the collecting locality. The species can be easily distinguished 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. We also provide an amendment to the existing diagnostic key to Lithocarpus, and discuss important differences with morphologically similar species found in Thailand and the surrounding region.

Keywords: Lithocarpus orbicarpus, new species, Stone Oaks, Fagaceae, Thailand, Ton Pariwat Wildlife Sanctuary

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.

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.

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.

Joeri Strijk, Sukontip Sirimongkol, Sukid Rueangruea, Nikom Ritphet, Voradol Chamchumroon. 2014. Lithocarpus orbicarpus (Fagaceae), a new species of Stone Oak from Phang Nga province, Thailand. PhytoKeys. 34 (2014) : 33-46. doi: