Diplodiscus latifii R.C.K.Chung, 2020

Chung, Richard Cheng Kong & Soepadmo, Engkik, 2020, Diplodiscus latifii (Malvaceae - Brownlowioideae), a new species from Sabah, Malaysia, PhytoKeys 161, pp. 99-106 : 99

Diplodiscus latifii R.C.K.Chung sp. nov. Figures 1 , 2A-C

Diagnosis.

Diplodiscus latifii is closely related to D. longifolius in leaf margin, midrib, inflorescence position, flower number, calyx shape, androgynophore length and shape and fruit indumentum. However, the former differs from the latter by its dark brown to black twigs (vs. grey to light brown), elliptic to broadly elliptic leaves (vs. narrowly elliptic or obovate), densely covered in brown dentate-lepidote scales with scattered dark brown subentire-lepidote scales below (vs. densely covered in light brown stellate-lepidote scales), coriaceous leaf texture (vs. chartaceous), acute apex (vs. acuminate), densely dentate-lepidote scaled petioles (vs. densely light brown stellate-lepidote scaled or glabrescent), ellipsoid flower buds, 3.5-4 mm in diameter (vs. spheroid, 2-3 mm in diameter), ca. 2.5 mm width of petals (vs. ca. 4.5 mm width), ellipsoid ovary (vs. oblate) and ellipsoid fruits to 7 mm in diameter (vs. broadly ellipsoid and more than 10 mm in diameter). The main morphological differences between these two species are shown in Table 1 .

Type.

Borneo, Sabah, Lahad Datu, Silam, Mile 14, 11 January 1966, Ahmad Talip SAN 52945 (holotype: SAN!; isotypes: K (sheet 1)!, K (sheet 2)!).

Description.

Small tree ca. 10 m tall, to 9 cm in diameter. Bark smooth, whitish; inner bark orange. Twigs rounded, 6-10 mm in diameter, glabrous and smooth, dark brown to black when dried. Stipules caducous. Leaves alternate, yellow brown with scattered tiny black dots below, coriaceous, densely covered in brown dentate-lepidote scales with scattered dark brown subentire-lepidote scales below, glabrous above; blades elliptic to broadly elliptic, (12.5-)15.5-20(-22) × (5.5-)8.5-10.5(-13) cm, base oblique, subcordate, margin entire, apex acute; midrib rounded, prominent below, raised above, glabrescent to glabrous below, glabrous above; lateral veins 8-10 pairs, prominent on both sides, looping near margin forming conspicuous intramarginal veins, basal pair of veins prominent on both sides, ascending to ¼ of the blade length; tertiary veins reticulate, prominent on both sides; petioles stout, transversally cracked, 7-14 mm long, 2-4 mm thick, densely covered in brown dentate-lepidote scales. Inflorescences terminal and axillary, panicles of 3-4(-5)-flowered cyme-like units, 15-23 cm long, 0.3-0.5 cm wide, lax, peduncles and rachis pale yellowish-brown, rounded, densely covered in stellate- and dentate-lepidote scales; bracts and bracteoles caducous, rarely persistent. Flowers bisexual, actinomorphic, pedicellate; buds ellipsoid or rarely spheroid, 4-5 × 3.5-4 mm, densely covered in stellate- and dentate-lepidote scales; pedicels 2-4(-5) × 1-2 mm, densely covered in stellate- and dentate-lepidote scales. Calyx bell-shaped, pale yellowish-brown; ca. 6 mm long; lobes 5, triangular, valvate, erect, 2-3 mm long, apex acute, densely covered in stellate- and dentate-lepidote scales abaxially, glabrous adaxially. Petals 5, white, spathulate, ca. 9 × 2.5 mm, base gradually tapering, apex emarginate, glabrous on both sides. Androgynophore short, cylindrical, ca. 1 mm long, glabrous. Staminodes 5, lanceolate, ca. 4 × 0.8 mm, shorter than filaments of fertile stamens, glabrous. Fertile stamens numerous; filaments arranged in 5 obscure phalanges, slightly connate at base, ca. 5 mm long, glabrous; anthers 0.6-0.8 mm in diameter. Ovary ellipsoid, ribbed, ca. 4 × 2.5 mm, densely stellate hairy, carpels 5, united, each carpel with 2 ovules; style 1, ca. 4.5 mm long, glabrous; stigma punctiform. Infructescences to 15 cm long, densely covered in stellate- and dentate-lepidote scales. Fruits ellipsoid, ribbed, 6-10 × 4-7 mm, densely stellate hairy; stalk ca. 2 mm long, ca. 1.5 mm thick, sparsely covered in stellate- and dentate-lepidote scales; pericarp ca. 1.5 mm thick. Seed 1(-2).

Distribution.

This species is endemic to Sabah, known from Silam, Lahad Datu.

Ecology.

Lowland mixed dipterocarp forest, yellowish soils, near stony stream at about 180 m elevation.

Vernacular names.

Pinggau-pinggau, takalis.

Etymology.

This species is named after the current Director-General of the Forest Research Institute Malaysia, Datuk Dr Abd. Latif bin Mohmod, for his strong support in conservation of karst limestone hills and plant diversity in Malaysia. He is the first and only forestry scientist ever honoured with a Malaysian National Young Scientist Award in 1993, two national science awards and six Malaysia Book of Records recognition awards.

Discussion.

Diplodiscus latifii is an endemic, rare tree. It is known only from one collection from Silam, Lahad Datu, Sabah. The newly-described species is morphologically most similar to D. longifolius in having an entire leaf margin, rounded midrib, terminal and axillary inflorescences with 3-4(-5)-flowered cyme-like units, bell-shaped calyx, short cylindrical androgynophore and densely stellate-lepidote ribbed fruits. However, D. latifii can be easily distinguished from D. longifolius by the morphological characters in Table 1 .

Morphologically, Diplodiscus latifii is also closely allied to the other four species found in Malaysia (i.e. D. hookerianus , D. microlepis , D. parviflorus and D. scortechinii ) in having asymmetrical leaf bases, entire leaf margin, short petioles, lax panicles and united carpels. Nevertheless, this new species can be distinguished from these four species by its dark brown to black twigs, densely covered in brown dentate-lepidote scales with scattered dark brown subentire-lepidote scales below its elliptic to broadly elliptic leaves, prominent lateral and tertiary veins on both surfaces, basal pair of lateral veins ascending to ¼ of the blade length, larger flower buds greater than 2 mm in diameter, ellipsoid ovary and ribbed ellipsoid fruits. With the addition of this new species, there are now six species of Diplodiscus in Malaysia and a key to these species is provided below:

Figures

Figure 1. Diplodiscus latifii A fruiting leafy twigs B leaf lower surface densely covered in dentate-lepidote scales with scattered subentire-lepidote scales C inflorescence D mature flower bud E longitudinal-section of flower F opened flower with parts of the calyx and two petals removed G flower with the calyx, petals and stamens removed H flower showing androgynophore and pistil I petals, abaxial view (right) and adaxial view (left) J stamens, lateral view (right) and slightly to top view (left) K staminodes, abaxial view (right) and adaxial view (left) L fruit with ridges and stellate trichomes M longitudinal-section of fruit N cross-section of fruit with one developed and four aborted seeds O cross-section at the centre of ovary P stellate trichome on the ovary surface. All drawn from the type. Drawn by Joseph Pao.

Figure 2. Diplodiscus latifii (A-C) and D. longifolius (D-F) A lower surface of leaves with scattered prominent black dots and densely small pale brown scales observed under low magnification B lower surface of leaves densely covered by brown dentate-lepidote scales with scattered dark brown subentire-lepidote scales C petiole densely covered by brown dentate-lepidote scales D lower surface of leaves densely covered by light brown stellate-lepidote scales observed under low magnification E leaves densely covered by light brown stellate-lepidote scales F petiole densely covered by light brown stellate-lepidote scales.