Lophopetalum tanahgambut Randi, Utteridge & Wijedasa, 2022

Randi, Agusti, Wijedasa, Lahiru S. & Utteridge, Timothy M. A., 2022, Lophopetalum tanahgambut, a new endemic giant tree species from peat swamp forest of Sumatera, Indonesia, with the first pseudoverticillate leaf arrangement in genus Lophopetalum (Celastraceae), Phytotaxa 573 (1), pp. 115-122 : 116-120

Lophopetalum tanahgambut Randi, Utteridge & Wijedasa , sp. nov. ( Figs 1–2 ).

Type:— INDONESIA. Sumatera Selatan Province: Musi Banyuasin Regency, Bayung Lencir District, Muara Medak Village, conservation area of PT Tri Pupajaya forest production concession, 10 m. elev., 1°45’30.66”S, 104°12’19.13”E, 17 April 2021, Randi GB-129 (holotype: BO!; isotypes: WAN!, FIPIA!, SING!) .

Diagnosis:— This species is the only known Lophopetalum with 3–4 leaves in a pseudoverticillate arrangement, leaf apex retuse to emarginate, petiole with a pair of ridges to conspicuously winged, panicles solitary in terminal leaf, calyx lobes much wider than long, disk convex, 5-angular with rounded corners, slightly thickened at lobe edges where the stamens are inserted.

Large top canopy tree, up to 40 m tall and 105 cm dbh; buttresses narrow, to 1.8 m tall; stilt-roots absent or sometimes present on old trees; knee roots system wide, to 15 m around the tree, raised to 1.5 m high from the ground surface, smooth, milky white to greyish. Bark smooth, cracked longitudinally to flaky, light to dull grey, or milky white; inner bark pinkish orange to pale reddish brown; sapwood cream. Lateral branches pseudoverticillate from seedling to pole and sometimes to early mature tree stage; young twigs with 3–4 obtuse angular, glabrous, plain green to becoming light and dull brown by aging, nodes thickened. Leaves in pseudoverticils of 3–4, arranged at a single plane around the axils or somewhat unequally within a node; blade coriaceous, often obovate or elliptic, sometimes lanceolate to oblanceolate, 6.1–12.4 × 3.0– 6.6 cm; base cuneate to slightly winged onto petiole; margin entire, recurved; apex retuse to emarginate or sometimes shortly acuminate; adaxial surface flat, slightly bullate to furrowed above, dark green, glabrous, often with scattered black dots on young leaves; abaxial surface with visible scattered reddish-brown gland dots, pale green to whitish when fresh, glabrous; midrib prominent on both sides; secondary veins slender, 8–12 pairs, arching for whole length, anastomosing to margin, slightly raised on both sides or sometimes sunken adaxially; tertiary venation reticulate, visible on both sides when fresh, flat to sunken adaxially or sometimes slightly raised; young leaves pale reddish-brown, shiny. Petiole 0.7–1.2 cm long, stout, ascending, slightly twisted, with a pair of ridges to conspicuously winged, shallowly channelled or flat to slightly convex adaxially, rounded abaxially, yellowish green when fresh, glabrous, sometimes pruinose when old. Panicles borne from terminal leaf axils, solitary in an axil, up to 11.5 cm long, branching to 2-orders, each branchlets bearing solitary flower, glabrous throughout, dull white to yellowish cream or greenish white when fresh; peduncle 2.5–4.5 cm long; rachis and branches 4-angular; branches arranged (sub)opposite, spiral or in pseudoverticillate; bracts persistent, wide triangular, 1.0-1.4 × 1.9–3.5 mm, apex acuminate, drying early; bracteoles consistently in a pair at the end of branchlet, ca. 1.0 × 1.4 cm, thickened and fleshy. Flower buds short conical to ovoid, as high as wide or wider than high, 2.2–3.8 × 2.2–4.1 mm. Flowers 8.5–9.2 mm diameter at anthesis; pedicel 4.0– 6.4 mm long; calyx lobes widely ovate, much wider than long, ca. 1.1 × 2.2 mm, apex rounded or sometimes obtuse, margins erose, papillate outer side, milky white; petals 5, imbricate, triangular or sometimes elliptic-oblong, 3.8–4.1 × 2.8–3.0 mm, white, glabrous on both sides, apex rounded to obtuse, margins erose, translucent, appendage conspicuous on the inner side, slightly sunken and papillate on outer one; disk convex, 4–5 mm diameter, 5-angular with rounded corners, slightly thickened at lobes edges, dull white to pale yellow when fresh; stamens 5, inserted near disk lobes edge; filament whip-like, 1.3–1.8 mm long, thickened at base and tapering at the end; anther medifixed, ovoid, ca. 1.1 × 0.8 mm, base cordate, apex acute to slightly attenuate; pistil emerging 2.0– 2.2 mm above the disk; ovary partly immersed in the disk, distinctly pyramidal at half base then narrowed into a cylindrical style; ovule 3–5 in each cell. Fruit generally ellipsoid, rarely oblong, 3-lobed, 5.5–10.5 cm long, 2.4–3.2 cm at the widest point, distinctly three-lobed in cross section, greenish yellow when mature, glabrous and flat surface when fresh, apex shortly acuminate, split open while still hanging to release the winged seeds; dried fruit tuberculate on outer surface, rusty brown. Seed attached in the middle, surrounded by wing entirely, flattened, 4.4–5.6 × 1.2–1.5 cm (wing included), seed proper cream, wing milky white, drying early before fruit splits.

Distribution:— The species is only known from peat swamp forests habitats in the type locality ( Fig. 3 ). The type locality is a High Conservation Value Forest in a pulpwood concession on the border of Berbak Sembilang National Park. The peat swamp forest spans the border between Jambi and South Sumatra Provinces. A wider distribution in similar peat swamp forest habitats along the east coast of Sumatera is possible. However, large scale conversion and degradation of peatlands in the past has fragmented and reduced the extent of intact peat swamp forest. As this species has only been found in intact peat swamp forests and not degraded or restoration sites in areas adjacent areas to the type swamp forest its actual extent under current peatland conditions is most likely limited ( Wijedasa et al., 2020).

Ecology and phenology:— In intact peat swamp forest with soil conditions that are always wet to flooded. In its type location, this new species is relatively rare and its seedlings are found very far from mature trees, this is probably due to the mechanism of winged seeds dispersing the seeds far from the parent trees. Lophopetalum tanahgambut was observed flowering during February–April, and fruiting in April–June.

Etymology:— The specific epithet ‘tanah gambut’ is formed from the Bahasa Indonesian words for peat soil or peat swamp habitat where this species is found.

Vernacular name:— Kerupuk, Perupok (Palembang Malay); this vernacular name is also used for all species of the genus Lophopetalum , as well as several Kokoona species.

Uses:— The wood is used locally for carpentry.

Additional examined specimens:— INDONESIA. Sumatera Selatan Province: Musi Banyuasin Regency, Bayung Lencir District, Muara Medak Village, conservation area of PT Tri Pupajaya forest production concession, 10 m. elev., 31 January 2022, Randi GB-141 ( BO) ; Sumatera Selatan Province: Musi Banyuasin Regency, Bayung Lencir District, Muara Medak Village, near Benu River , 10 April 2022, Randi GB-150 ( BO) .

Provisional conservation status assessment:— Critically Endangered: CR A2cd C2a(i) ( IUCN 2019). Lophopetalum tanahgambut grows in relatively undisturbed lowland peat swamp forest, which is protected by voluntary commitment of the concession as a conservation and retirement area. More extensive collecting in the wider area may reveal otherwise, but for now we must assume a small population size and a restricted distribution in Sumatera. While overall, undisturbed peat swamp forests have declined and under threat across Southeast Asia, and most remaining peatlands are converted to agriculture or degraded due to drainage ( Miettinen et al. 2017; Page et al. 2022).

Notes:— We have observed many trees in various life stages (seedling, sapling, pole to large tree) in the wild, and the pseudoverticillate leaves are consistent. Opposite (or subopposite) leaves as usually found in the genus but does not occur in this new species. On older branches we sometimes found opposite leaves but usually there is also a leaf scar slightly below them indicating they are not oppositely arranged from the beginning, but shift in position as the branchlets mature. If a twig is 3–4 angular depends on the number of leaves at a node, and this is clearly visible when the twigs are still young.

The pseudoverticillate leaf arrangement of 3–4 leaves, and the associated 3–4 angular twigs, together with the retuse to emarginate leaf apex, and petiole with a pair of ridges to being conspicuously winged, comprise a unique set of vegetative characters for this species that have not been encountered in Lophopetalum previously, including all the species in Sumatera. Floral parts of L. tanahgambut superficially resemble L. rigidum Ridl. ( Ridley 1931: 38) , but can be differentiated by a combination of characters including its longer pedicels (4.0– 6.4 mm vs. 2–3 mm), larger flowers at anthesis (8.5–9.2 mm vs. 3.5–6.0 mm), different shape, dimension and size of calyx lobes (widely ovate, much wider than long, 1.1 × 2.2 mm, apex rounded vs. ovate or triangular, longer than wide, 1.3–1.5 × 1.0 mm, apex acuminate), petals with conspicuous appendages on inner side (vs. naked), and disk convex, 4–5 mm diameter (vs. roughly flat, 1.5–3.5 mm); in addition, L. tanahgambut is a large tree found in Sumatera, while L. rigidum is a small tree (to c. 12 m tall) endemic to Borneo.

In the key to Malesian Lophopetalum ( Ding Hou 1962: 264) , this species would key out to the group of species having short conical flower buds with distinct appendages on the inner surfaces and having a disk greater than 4.5 mm in diameter: L. pachyphyllum King , L. wightianum Arn. and L. macranthum (Loes.) Ding Hou , with first two found in Sumatera and the latter species a New Guinea endemic. In addition to the unique leaf arrangement of L. tanahgambut , the new species differs from L. pachyphyllum and L. wightianum in the obscurely 5-angular disk rather than being distinctly lobed with the lobes or angle epipetalous, which is particularly pronounced and red to deep purple-red in L. wightianum . Of the other five taxa found in Sumatera, L. beccarianum Pierre , L. javanicum (Zoll.) Turcz. , L. multinervium Ridl. , L. pallidum M.A.Lawson and L. subobovatum King , in addition to the pseudoverticillate leaf arrangement, these species differ in the floral structure with L. beccarianum having flattened buds and the four other species all having a much smaller disk, usually less than 3 mm in diameter.

Figures

FIGURE 1. Lophopetalum tanahgambut Randi, Utteridge & Wijedasa.A. Base of the trunk on mature tree.B. Knee roots system.C.Twig with infructescence. D. Adaxial surface (upper) and abaxial surface (below) of leaves. E. Young tip of twig with three pseudoverticillate leaves. F. Winged petiole and base of blade. G. Leaf apex. H. Older branch with four pseudoverticillate leaves. All photos by A. Randi from holotype (Randi GB-129).

FIGURE 2. Lophopetalum tanahgambut Randi, Utteridge & Wijedasa.A. Panicle. B.Anthesis flower and buds. C. Flower (side view). D. Flower (top view). E. Fruit (side view). F. Cross section of fruit.G. Ripe fruit splits and seeds. Photos A–D from A. Randi (Randi GB-150); photos E–G from A. Randi (Randi GB-141).

FIGURE 3. Distribution map of Lophopetalum tanahgambut Randi, Utteridge & Wijedasa (red dot).