Lithocarpus tapanuliensis Harapan, W.H.Tan, Nurainas & Strijk, 2023

Harapan, Try Surya, Tan, Wei Harn, Febriamansyah, Thoriq Alfath, Nurainas,, Syamsuardi, & Strijk, Joeri Sergej, 2023, Lithocarpus tapanuliensis (Fagaceae), a new stone oak from northern Sumatra and its role as an important resource for critically endangered orangutans, PhytoKeys 234, pp. 167-179 : 167

Lithocarpus tapanuliensis Harapan, W.H.Tan, Nurainas & Strijk sp. nov.

Fig. 1

Type material.

Holotype. Indonesia, North Sumatra Province, South Tapanuli Regency, Sipirok District, Bulu Mario Village, Pilar Forest (Fig. 2 ). 1°34'53.9"N, 099°11'38.2"E, elevation 894 m, 23 February 2023, Holotype: ANDA [ANDA00000051794]; Isotypes: ANDA [ANDA00000051793].

Diagnosis.

Lithocarpus tapanuliensis distinguishes itself from similar species through its presence and placement of unique bullate protuberances covering the cupule and the distinct presence of a narrow ring of small denticulated plates around the rim. It differs from L. elegans (Blume) Hatus. ex Soepadmo with tiny, pointed scale-like appendages, L. confragosus (King ex Hook.f.) A.Camus with close-set warts, L. corneus (Lour.) Rehder with the diamond-like pattern and L. pulcher (King) Markgr. with tuberculate cupules. The cupule of L. tapanuliensis covers almost 3/5 of the nut (in contrast with L. pulcher and L. confragosus , whose cupule encloses almost the entire nut). The surface of the cupule is slightly tomentose and dark brown with distinct protuberances (whereas L. confragosus , L. corneus and L. pulcher lack such because of the absence of lamellae) (Table 1 ).

Description.

A large tree without buttresses, up to 35 m tall. Bark rough, lightly fissured, greyish-green with whitish lenticel. Inner bark is dark red forming longitudinal slits. Twigs diameter 0.2-0.4 cm, smooth, striate, bud imbricate 0.5 mm. Branches dark brown. Leaves simple, underneath tomentose, dark green above and fawn green below when fresh; above, dull greyish-brown, lightly brown when dry. Blade elliptic-oblong, 16.5-20 (L) × 6-8.5 (W) cm; margin entire; apex cuspidate tip; bases attenuate. Petiole: striate, glabrous, 1.3-1.5 cm in length. Venation mid-rib wide, raised on both sides; pinnately veined, secondary venation eucamptodromous. Pairs of secondary nerves 10-11 pairs, raised on the underside. Tertiary veins sub-scalariform. Male and female inflorescences not seen. Peduncles up to 2-4 cm long and between 0.3 and 0.5 cm in diameter. Infructescence rachis diameter 0.4-0.5 cm. Acorn solitary along the rachis and spaced both in immature and mature stages. Cupule solitary and sessile, greenish-brown when fresh, mature cupules cup-shaped covering half of the nut, diameter 2.8-3.4 cm, cupule thickness 2.4-2.8 cm. thick-walled woody, cupule surface irregular, with a narrow ring of small denticulated plates around the rim, rest of cupule covered in distinct bullate protuberance gradually fusing into large tumour-like masses towards the base. Protuberances, specifically the rim, have resin burn marks with blackish shiny colour when dried. Immature cupules thin, cup-shaped covering 80% of the nut, covered in small protuberances ranging from relatively flat lines to bullate. Nut obovoid, length 1.9-2.3 cm, diameter 2.2-2.6 cm, sparsely tomentose around the basal scar, fawn-green when ripe, brownish-grey when dried, basal scar depressed, nut scar diameter 1.6-1.7 cm, thickness 0.3-0.4 cm. Resin leaking on the nuts. Apex flattened obtuse.

Phenology.

Fruiting was observed in February 2023 with fresh fruits recovered from the tree and from the ground.

Distribution, habitat and ecology.

During our fieldwork in Pilar Forest, a primary forest near the Bulu Mario District, we recorded two individuals of Lithocarpus tapanuliensis . The lower-montane forest is characterised by the abundance of meranti gunung ( Shorea platyclados Slooten ex Endert). Additional Fagaceae species were recorded, namely Lithocarpus javensis Blume, Quercus oidocarpa Korth. and Castanopsis tungurrut (Blume) A.DC. Interactions with Tapanuli orangutans were observed with a nest and remnants of consumed fruits were recorded near the tree (Fig. 3 ). Sipirok Regency precipitation typically varies during different sections of the year. Maximum monthly precipitation is 296.5 mm and the minimum monthly precipitation is 67 mm, with an average temperature around 28 °C (Badan Pusat Statistik 2023).

Vernacular name.

Hoteng (Tapanuli language).

Etymology.

The epithet is derived from its type locality, Tapanuli, South Tapanuli District, Sipirok Regency, North Sumatra Province, Indonesia.

Conservation status.

Using the guidelines established by the IUCN Red List ( IUCN Standards and Petitions Committee 2022), we provide an initial conservation assessment of the species as Critically Endangered (B1ab(iii) + B2ab(iii), D), based on only two recorded individuals within Pilar Forest, its limited range and extensive habitat alteration and forest clearance in the immediate vicinity of the forest and throughout Sumatra. Pilar Forest does not have any legal protection or governance, but is immediately adjacent to Dolok Sibual-buali Nature Reserve. Both are part of the wider Batang Toru ecosystem landscape (150,000 ha; Fredriksson and Usher (2017)). Under this programme, the area is targeted for protection, ecosystem restoration and sustainable tourism development through a combination of NGOs and the State. More information and images are available on the species webpage (www.asianfagaceae.com/lithocarpus_tapanuliensis/) and GBIF.

Figures

Figure 1. Lithocarpus tapanuliensis Harapan, W. H. Tan, Nurainas & Strijk, sp. nov. A fresh fruits from field collection B fresh fruits in the canopy C bark and sapwood D fresh leaves E dried mature and immature infructescence F base of tree next to an animal wallow G cupule- bottom view, top view and nut bottom view and cross-section. Pictures by T. S. Harapan & T. A Febriamansyah, edited by W. H. Tan.

Figure 2. Distribution map of Lithocarpus tapanuliensis sp. nov. in South Tapanuli, North Sumatra. The inset map shows the location of the sampling region on Sumatra Island, Indonesia. Elevation was obtained from SRTM (2023). Map by T. S. Harapan.

Figure 3. A Acorns consumed by orangutan B orangutan nest in a neighbouring tree. Pictures by T. S. Harapan & T. A Febriamansyah, edited by W. H. Tan.