Differs from other members of the subgenus Tetrardisia in having linear-oblong leaves, with a long, acuminate-caudate apex, and finely serrulate margins.

INDONESIA. Borneo: Central Kalimantan, Kotawaringan [Kotawaringin] Timur, S. Mentaya, km 92 from Sangai, Plot 8, [1°18’S, 112°32’E], 100 m elevation, 18 May 1993, Argent et al. 93187 (holotype E!; iso: BO).

Figure 1. 

Ardisia argentiana Julius & Utteridge, sp. nov. A habit B stem with flexuose line C venation details on lower surface D mature flower E flower bud F calyx G corolla lobe, abaxial view H open corolla and stamen I ovary and pistil. (Drawn by Hazel Wilks from Argent et al. 93187).

Shrub ca. 1 m high; stems sparsely scaly when young, soon glabrous, slightly flexuous, winged between the nodes with raised lines running along the internodes between the petiole bases. Indumentum of sessile, circular, peltate scales up to 0.05 mm in diameter, on young parts, leaves and inflorescence. Leaves alternate; petioles 3–5 mm long, winged by the decurrent leaf base, glabrous; lamina chartaceous, linear-oblong, (7–)10–11.5 × 1–2 cm, with dense gland-dots throughout apex acuminate-caudate, acumen 1–2.5 cm long; base cuneate, between the higher order venation, lacking hairs, sparsely scaly on the lower midrib, glabrous above, midrib sunken above, raised beneath; lateral veins ca. 48 pairs, semicraspedodromus, and with 1–2 intersecondary veins within each pair; intercostal veins obscure. Inflorescences terminal on lateral branches, proximally laxly paniculate with subumbellate branches with 2-flowers distally racemose; peduncle and rachis (1.5–)2.5–4 cm long, slightly flexuose, sparsely scaly; bracts linear-lanceolate, (0.4–)1.5–1.7 × 0.4 mm, very sparsely ciliate with few scattered hairs. Flowers ca. 8; pedicels slender, ca. 1.5 cm long, sparsely scaly; calyx-lobes 4, green, gland-dotted, lacking hairs, sparsely scaly outside, ovate, ca. 1 × 0.8 mm, apex acute, margin very sparsely ciliate with few scattered short hairs; corolla-lobes 4, reflexed, twisted apically, white with orange-brown elongated-dots, lanceolate, 6.4–7 × 1.7–2.3 mm, glabrous on both surfaces; stamens 4, spreading upright (in open flower), filament ±sessile, anthers twisted apically, lanceolate, ca. 5–6.2 × 0.8 mm, apex elongated into a hyaline tip, thecae open by longitudinal-slits, with scattered, lineate, orange brown dots behind, glabrous; ovary ovoid, ca. 7 × 6 mm, style and stigma filiform, ca. 6.8 mm long, ovules ca. 6 in 1-series. Fruits n.v.

Endemic to Borneo; known only from Sungai Mentaya, Kotawaringin Timur, Central Kalimantan.

The species epithet commemorates Graham Charles George Argent (1941–2019), a prominent botanist on tropical botany in South-East Asia and a leading expert on Ericaceae, especially the tropical ‘Vireya’ rhododendrons, and collector of the type material.

Data deficient (DD). The only specimen available was collected in 1993 and the species is known only from a single collection location south of Bukit Raya in Central Kalimantan, and thus meets the B1a criterion for Critically Endangered (CR) status. The species was found to the south of the Bukit Baka – Bukit Raya National Park, and, to date, there are no further collections of the species from inside this protected area. Satellite imagery in Google Earth from 2015 shows that the collection locality still has some forest coverage and was not penetrated with roads or logging tracks, and it also appears to not have been converted for agricultural use such as oil palm plantations. However, lack of collections and field observations of the species do not allow inference of decline or fluctuation in population size or EOO and AOO, and we are unable to fulfil the criteria to preliminary assess this species as Critically Endangered.

Ardisia argentiana is a distinct species on account of the combination of branches with wing-like raised lines running between the petiole bases, linear-oblong leaves less than 2 cm wide with finely serrulate margins, the terminal, laxly paniculate inflorescence with a hairy scaly rachis and few, tetramerous flowers. This new species is morphologically similar to Ardisia nagaensis, but differs from that species in leaf morphology, especially the shorter pedicels (A. argentiana 3–5 mm long; A. nagaensis 1.5– 3 cm long), linear-oblong leaves less than 2 cm wide (A. nagaensis elliptic-lanceolate to 5.5 cm wide) and the fewer flowered inflorescence (A. argentiana with 8 flowers vs. A. nagaensis with 24).

The flower is described as ‘white’ in the specimen label which probably refers to the corolla and anthers. The leaf resembles Ardisia mystica. B.C. Stone (Stone 1982), a member of subgenus Pimelandra, but all members of that subgenus have short, axillary inflorescences. Similar wing-like ridges along the internodes are found in species of Systellantha, a genus of three species endemic to northern Borneo (Drinkell and Utteridge 2015). Members of Systellantha are understorey small trees or shrubs to only 3 m, are also tetramerous but have unisexual flowers with the plants being monoecious. The wing-like ridges may be a response to ecological conditions, such as high humidity, in the rainforest understorey.

Similar to Ardisia tetrasepala in its simple and compact inflorescence with corymbose flowers but differs mainly vegetatively in having leaves laxly arranged, longer petioles that are covered with glandular hairs, a chartaceous lamina without marginal secondary veins, surface with scattered stellate hairs near the margin beneath and leaf base obtuse or ±cuneate. The corolla lobes are smooth without lepidote scales (vs. lepidote scales present in A. tetrasepala).

MALAYSIA. Borneo: Sarawak, Tatau District, Ulu Merirai, Gua Naga, [02°39’12”N, 113°03’05”E], 11 July 2005, Julia et al. S95726 (holotype KEP!; iso: SAR, SING)

Figure 2. 

Ardisia nagaensis Julius, T. Kajita & Utteridge, sp. nov. A habit B glandular hairs on stem C erect, simple hairs on petiole D the venation close-up E stellate hairs close-up F enlarged inflorescence G flower bud H mature flower I open calyx J open corolla with stamen K corolla lobe L stamen, front and back view M placenta and ovules. (Drawn by Mohamad Aidil Noordin from Julia et al. S95726).

A small shrub, less than 1 m high; stems glabrescent, slightly flexuous, winged between the nodes with obscure raised lines running along the internodes between the petiole bases. Indumentum of simple, short (stalked), glandular, or stellate (star-liked), pale brown to rusty hairs (visible under microscope). Leaves alternate; petioles 1.5–3 cm long, sparsely to densely hairy towards midrib, simple, short, glandular hairs; lamina chartaceous, with dense gland-dots throughout the leaf, glabrous on both surfaces except for margin with scattered stellate hairs beneath, elliptic-lanceolate, 17–19 × 5–5.5 cm, apex long acuminate and slightly caudate with acumen 1.5–2.0 cm long; base obtuse or ±cuneate, margin obscurely denticulate being entire in appearance, midrib flat or slightly sunken above, raised beneath, glabrous except hairy with glandular hairs beneath, denser near leaf base; lateral veins 13–15 pairs, distinct above, prominent beneath, inter-secondary veins present in between; intercostal veins percurrent, distinct beneath. Inflorescence terminal on lateral branches, simple with flowers arranged in corymbs; peduncle and rachis 4–5 cm long, densely hairy with glandular hairs; bracts ovate to elliptic, 0.5–1.5 mm long, hairy with glandular hairs. Flowers ca. 24; pedicels slender, 1.2–1.8 cm long, up to 2 cm long in fruiting, covered with dense, glandular hairs; calyx-lobes 4, purplish, gland-dotted, lacking hairs, broadly ovate, 1–1.5 × 1–1.5 mm, apex obtuse, margin incised, sparsely ciliate with short, thick hairs; corolla-lobes 4, reflexed, twisted apically, purplish with transparent margin, lanceolate, ca. 8 × 2.5 mm, glabrous on both surfaces; stamens 4, spreading upright (in open flower), filament ±sessile, anthers twisted apically, lanceolate, ca. 6 × 1 mm, apex without a prolonged hyaline tip, thecae opening by longitudinal slits, with lineate, black dots behind, glabrous; ovary globose, ca. 1 × 0.8 mm, style and stigma filiform, ca. 6 mm long, ovules 4–6 in 1-series. Fruits ripe bright red, globose, ca. 6 × 5 mm.

Endemic in Borneo, Sarawak; known only from Gua Naga, Ulu Merirai area, Tatau District.

Ardisia nagaensis is very local and was found at only one locality, Gua Naga, for which it is named.

Data deficient (DD). The only specimen available was collected in 2005 and the species is known only from a single collection location from Ulu Merirai in Central Sarawak, and thus meets the B1a criterion for Critically Endangered (CR) status. The Ulu Merirai region is an area of sandstone with limestone cliffs, and supports several point endemics, including several newly described species of Begonia L. (Kiew and Sang 2009) and Monophyllea R. Br. (Kiew and Sang 2013). The species was found outside of any protected area, but satellite imagery in Google Earth from 2017 shows that the collection locality has undisturbed forest coverage and was not penetrated with roads or logging tracks. However, lack of collections and field observations of the species do not allow inference of decline or fluctuation in population size or EOO and AOO, and we are unable to fulfil the criteria to preliminary assess this species as Critically Endangered.

Compared to the other members of subgenus Tetrardisia, this new species described here has an affinity with A. tetrasepala, endemic to Peninsular Malaysia [Johor, Gunung Pulai]. This is because both are characterized by a simple and compact inflorescence, whereas other taxa in xTetrardisia have compound and laxly flowers arranged. Ardisia nagaensis differs from A. tetrasepala by the leaf characters viz. the petiole length (A. nagaensis with 1.5–3 cm long vs. A. tetrasepala with 0.5–0.8 cm long), the leaf base (A. nagaensis with obtuse or ±cuneate leaf base vs. A. tetrasepala with cordate-rounded) and the venation (A. nagaensis without marginal secondary veins vs. A. tetrasepala with marginal secondary veins). Further morphological comparison between these two species is given in the Table 1.

The calyx is described as ‘purplish’ in the specimen label which probably refers to both the calyx and corolla. The corolla margin on one side is transparent as observed in A. denticulata.