Ardisia argentiana Julius & Utteridge, 2020

Julius, Avelinah, Kajita, Tadashi & Utteridge, Timothy M. A., 2020, Two new species of Ardisia subgenus Tetrardisia (Primulaceae - Myrsinoideae) from Borneo, PhytoKeys 145, pp. 139-148 : 139

Ardisia argentiana Julius & Utteridge sp. nov. Figure 1

Diagnosis.

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

Type.

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).

Description.

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.

Distribution.

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

Etymology.

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.

Conservation status.

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.

Notes.

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.

Figures

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).