Trigonachras postardanjeisin Buerki & Callm., 2013

Buerki, Sven, Davidson, Christopher, Pereira, Joan T. & Callmander, Martin W., 2013, A new endemic species of Trigonachras (Sapindaceae) from Sabah, Malaysia (Borneo), Phytotaxa 88 (2), pp. 19-24 : 20-21

Trigonachras postardanjeisin Buerki & Callm. , sp. nov. ( Figs. 1–2 )

Haec species Trigonachradi acutae Radlk. ample distributae arcte affinis, sed ab ea inflorescentiae infructescentiaeque axibus glabris (vs. trichomatibus fulvis indutis in T. acuta ), fructu glabro (vs. brunneolo- vel in vivo rubellotomentoso) atque sepalis abaxialiter puberulis adaxialiter parce pubescentibus (vs. utrinque trichomatibus brevibus sericeis satis dense indutis) facile distinguitur.

Type:— MALAYSIA. Borneo: Sabah: Bukit Tangkunan , Tawai Forest Reserve , Jalan Microwave road, 117˚12’28’’ E, 5˚38’29’’ N, 263 m, 9 April 2012 (fl.), Buerki, Callmander, Davidson, Christoph, Postar, Jeisin & Nur 338 (holotype MO!; isotypes G [ G00368626 ]!, K!, L!, SAN!, SING!) .

= Trigonachras nov. sp. A fide Leenhouts (1988: 207).

Tree, 25–30 m tall, to 60 cm dbh, branches ca. 7 mm in diam. just below insertion of mature leaves, grey, glabrous. Leaves alternate, paripinnate, 14–26 cm long; petiole 4.5–5.5 cm long, ca. 2 mm in diam. at base, smooth, glabrous, enlarged at the base; leaflets (3–)5–7(–8) pairs, opposite to subopposite, blades concolorous, medium to dark green on both surfaces, subcoriaceous, stiff-pergamentaceous, elliptic to falcate, slightly asymmetric, 5–10 × 1.5–4 cm, glabrous on both surfaces, few domatia on lower surface, base strongly to distinctly oblique, acute, strongly attenuate, apex acute, margins slightly revolute; petiolules of largest leaflets (5–) 8–12 mm long, 0.5–1 mm in diam., slightly enlarged at the base. Inflorescence pseudoterminal, 15–20 cm long, green, glabrous except the pedicels that are tomentose. Flowers, ca. 1 cm long, in glomerules of 2–4 flowers, evenly borne along the ultimate axes; bracts subtending the inflorescence axes caducous (not seen), leaving an evident scar; pedicels 3–6 mm long, tomentose, densely covered with whitish trichomes at base. Sepals 5, broadly-ovate, pale green in vivo, brown when dried, ca. 2 mm long, ca. 4 mm in diam (all sepals are equal in size), outside puberulent with whitish trichomes, inside sparsely hairy with whitish trichomes. Petals 5, long-clawed (blade enlarged distally), white, veined, ca. 2–3 mm long, ca. 1.5 mm in diam, outside glabrous, inside sparsely pubescent with whitish trichomes; scales 1–2, triangular, densely covered by a whitish indumentum, not crested. Disc circular, brown, ca. 2 mm in diam. Stamens 7–8, with filaments ca. 3–4 mm long at anthesis, densely pubescent in the proximal part, anthers yellow, ca. 1 mm long. Ovary globose, ca. 0.8 mm high, 1 mm in diam, densely velutinous, indument pale brown. Immature fruit 3- angular-obovoid, ca. (2–)2.5(–3) x 1–1.5 cm, narrowed to the base, apiculate, glabrous; wall somewhat fleshy, at least 1 mm thick, endocarp densely woolly.

Distribution and habitat: — Trigonachras postardanjeisin is endemic to the lowland ultramafic forest in Bukit Tangkunan, Tawai Forest Reserve ( Fig. 1 ). This species is particularly abundant along the road to the summit at elevations from 180 to 260 m. The most significant ultramafic sites in Sabah are Mt Silam, Bidu- Bidu hills, Mt Tawai, Morou Porou, Mt Tambuyukon, Hampuan and Kulung Hills, Pig Hill, Marai Parai and Meliau Range. Ultramafic substrates are found from sea level (islands such as Pulau Sakar near Lahad Datu) up to nearly 3,100 meters of elevation (at Mt. Kinabalu). Several species are endemic to this particular substrate throughout Sabah, e.g. Daemonorops serpentina Dransfield (1982: 810) . Nevertheless, Trigonachras postardanjeisin is the only species that is currently restricted to Bukit Tangkunan, which is situated within the Tawai Forest Reserve.

Phenology: —Immature fruits have been collected in July and flowering material in April.

Etymology: —The new species is named in honor of Postar Miun and Jeisin Jumian, both working at the Sandakan Herbarium of the Sabah Forestry Department. Postar and Jeisin greatly contributed to the success of the field work in various regions of Sabah and are immensely contributing to the knowledge and conservation of the flora of this region.

Conservation status: —With an area of occupancy (AOO) of 9 km 2, and one subpopulation, situated within a forest reserve (Bukit Tangkunan), Trigonachras postardanjeisin is assigned a preliminary status of Vulnerable (VU D2) based on the IUCN Red List Categories and Criteria ( IUCN 2001) (calculation following Callmander et al. 2007). The Vulnerable Category is justified by the very restricted AOO that have a tendency to become Critically Endangered in a near future due to human activities or an unexpected event, e.g. fire.

Additional specimens examined (paratypes): — MALAYSIA. Borneo : Sabah: 2 miles up the microwave station, 180 m, 26 July 1972, Leopold & Amin SAN 75360 ( K, KEP, L, SAN!, SAR!, SING!) .

Discussion: — Trigonachras postardanjeisin is morphologically close to the widespread T. acuta ( Hiern 1875: 677) Radlkofer (1879a: 672) . The new species can, however, be easily discriminate by its glabrous inflorescence and infrutescence axes (pedicels are tomentose) and fruits (vs. fulvous indumentum on the inflorescence and infrutescence and brownish tomentum, reddish in vivo, on the fruit in T. acuta ); sepals puberulent on the outside and sparsely hairy on the inside (vs. fairly dense short sericeous indumentum on both sides). Trigonachras postardanjeisin is endemic to ultramafic soil in Sabah and so far known only from Bukit Tangkunan, whereas T. acuta is often growing on sandy soils in Sumatra, Peninsular Malaysia and Borneo.

Figures

FIGURE 1. Geographical distribution of Trigonachras postardanjeisin (shown in black solid circle).

FIGURE 2. Trigonachras postardanjeisin. A: immature fruit; B: stamen; C: branchlet with leaf and inflorescence; D: immature infrutescence; E: flower with detail of disc; F: flower with longitudinal section and details of petals and sepals. B, C, E, F from Buerki et al. 338 (G, L, MO); A, D from Leopold & Amin SAN 75360 (SING). Drawn by Roger Lala Andriamiarisoa.