Trigonobalanus verticillata Forman

Ng, SC. & Lin, JY. (2008). A new distribution record for Trigonobalanus verticillata (Fagaceae) from Hainan Island, South China. Kew Bulletin 63: 341. https://doi.org/10.1007/s12225-008-9026-x

Type

Mt Kinabalu, Liwagu R., Kundasang, 4 Sept. 1961, RSNB 2732a (holotype K; isotypes L, LE, US).

Distribution

South China (Hainan Island) (present study), Malaysia (Malay Peninsula, Borneo), Indonesia (Sulawesi, Sumatra) (Nixon & Crepet 1989).

Ecology

Two of the three populations were found on the southern slopes of the Mayuling Mountain which is continuous with Yinggeling Mountain, the second highest mountain on Hainan Island. S. C. Ng 5091 was found at a place locally called Nan-le-shan in montane tropical broadleaved forest at 1100 m, whereas S.C. Ng 5561 & 5575 and Lin & Mo 050474 were found in similar vegetation type at Po-chun-ling, 1200 m and 900 m respectively, about 7 km from the former site. The third population where S. C. Ng 5670 was collected was on the ridge (1400 – 1600 m) of Yinggeling Mountain about 18 km from the two previous sites. The species is locally common in tropical montane rainforest and evergreen broadleaf forest at the three sites. Major accompanying tree species included Castanopsis tonkinensis, Lithocarpus fenzelianus, Altingia obovata and Dacrydium pectinatum. It is occasionally abundant enough to become codominant with the above species.

Phenology

The specimen S. C. Ng 5561 was found to have staminate inflorescences with flowers just beginning to open during the survey in late Nov. 2005. A specimen with unripe infructescences (S. C. Ng 5670) was subsequently collected in May 2006. The fruiting specimens S. C. Ng 5575 and Lin & Mo 050474 were collected from a fallen tree which was probably blown down by a typhoon two months earlier, in Oct. 2005.

Conservation

The global conservation status of Trigonobalanus verticillatahas not been assessed (IUCN 2006).It was described as growing “gregariously” in montane forest in Peninsular Malaysia and Borneo (Soepadmo 1972)and was “commonly found” in some areas there (Kamiya et al. 2002,citing personal communications with K. C. Nixon & M. Hotta). Without firsthand data on the global distribution and populations of the species, we canonly assess its regional conservation status in China. Since Hainan Island isover 1,600 km from any previously known locality of the species, and thespecies shows very limited gene flow via seed (Kamiya et al. 2002),the Hainan population can be considered an effectively isolated breedingpopulation. The regional conservation status in China can, therefore, beassessed with the IUCN Red List Criteria (IUCN 2001)without any downgrade (IUCN 2003).So far only three populations have been confirmed in China and the area ofoccupancy of these populations is less than 20 km2, so the regionalconservation status in China should be ‘Vulnerable’ (VU D2). Given its biogeographical importance and restricted distribution in China and Hainan, immediate action to step up its in situ conservation, by setting up the proposed Yinggeling National Nature Reserve which includes the three known populations in Hainan, seems essential. The species should also be included into the National Protected Plant List of China.

Note

The species is a distinctive member of Fagaceae with leaves arranged in whorls of three and trigonous fruits and cupules arranged oppositely or in whorls. The specimens collected more-or-less conformed to the description in the above-cited literature. The authors have also compared the above specimens to flowering material from Sulawesi kept in the South China Botanic Garden, Guangzhou, (IBSC herb. no. 249616, coll. s.n.), and found no obvious differences in vegetative parts, except for the slightly denser and longer stellate hair cover on the rachis of the staminate inflorescence of the Sulawesi specimen. Such a difference is within the range mentioned in Forman (1964) & Soepadmo (1972). The distribution range of this species was previously only known in the wet tropical montane rainforest between about 7°N (Sabah & Fraser’s Hill) and 0° (Sulawesi) (Nixon & Crepet 1989), to 18°N on Hainan Island, which has a tropical moist monsoon climate with distinct dry and cool seasons. Trigonobalanus verticillata differs from the related Formanodendron doichangensis (Nixon & Crepet 1989) which has spirally alternate leaves and cupules on the inflorescence. The latter species was recorded from S and SW Yunnan in China as well as N Thailand and used to be included in the genus Trigonobalanus Forman as T. doichangensis Forman (Forman 1964; Hsu et al. 1981; Hsu & Jen 1998; also see Huang et al. 1999). Various morphological and palynological differences among the three species in Trigonobalanus sensu Forman suggested them to be in different genera (Nixon & Crepet 1989; Wang et al. 1998). This is further supported by substantial DNA sequence divergence among the three species compared to other genera of Fagaceae (Manos & Standford 2001), suggesting that they had diverged since ancient times. As a result, the discovery of T. verticillata in Hainan represents a new generic record (Trigonobalanus Forman sensu Nixon & Crepet (1989)) for China.

Morphology Branches

Branchlets trigonous, covered in sparse stellate hairs

Morphology General Habit

Tree up to 10 – 20 m tall, 30 – 70 cm dbh; bark pale grey-brown, smooth to shallowly fissured

Morphology Reproductive morphology Inflorescences

Staminate inflorescence 2.5 – 5 cm, unbranched or with up to three more or less equal branches towards base, male flowers in groups of 3 – 5, perianth 6-lobed, margin fimbriate, centre of adaxial side with pilose hairs Inflorescences and infructescences in axils of upper leaves or terminal, erect, clustered into terminal or sub-terminal paniculate clusters, sparsely covered with stellate hairs

Morphology Reproductive morphology Fruits Infructescences

Infructescences 5 – 6.5 cm, unbranched; ripe cupules sessile, opposite to whorled on rachis, occasionally single, enclosing 3 – 5 fruits, open, (3 –) 5 lobes, triangular, acute, adaxial side fulvous tomentose by appressed simple hairs, abaxial side fulvous stellate hairy and with 5 – 6 transverse rows of acutely dentate lamellae; fruit sharply trigonous, 5.8 – 6.4 mm long × 3.4 – 4.9 mm wide, sparsely stellate hairy; base truncate; scar flat triangular; apex acute.

Morphology Leaves

Leaves in whorls of three, coriaceous, 5.0 – 9.2 × 1.8 – 4.2 cm, obscurely and bluntly crenate in the distal half to entire, apex acuminate to obtuse or emarginate

Morphology Leaves Stipules

Stipules in whorls of three, ovate lanceolate 3.8 – 5.1 × 1.2 – 2.8 mm, caducous