Syzygium omissum Mansibang & Fernando

Fernando, E. S., Quimado, M. O. & Mansibang, J. A., 2024, Two New Species Of Syzygium (Myrtaceae) From Ultramafic Soils In Northeastern Mindanao, Philippines, With Notes On Three Other Rare Species, Edinburgh Journal of Botany 81 (2027), pp. 1-19 : 3-7

Syzygium omissum Mansibang & Fernando , sp. nov.

This species is most similar to the Bornean species Syzygium silamense P.S.Ashton in its nearly sessile leaves with cordate base, ovate-oblong lamina and terminal inflorescence. However, Syzygium omissum differs in its consistently shorter stature 3–5 m (vs taller, c. 10 m), rigidly coriaceous leaf texture (vs membranous), petiole and midrib deep black (vs petiole dark olive brown, midrib paler olive brown), epunctulate leaf surface (vs adaxially pitted, abaxially minutely punctulate), hypanthium black (vs dark olive brown), distal hypanthium limb 1.8–3.0 mm (vs c. 5 mm), hypanthium limb ovary-to-length ratio 1:1 (vs 2–3:1), and fruit style not persistent or c. 2 mm (vs 4 mm). Syzygium omissum is also similar to the Philippine species S. bernardoi (Merr.) Merr. ; however, it differs by having distinctly 4-winged young twigs and inflorescence axes (vs terete-sulcate);

leaf apex bluntly obtuse to rounded (vs acuminate); fruits 7–8(–9) × 6–8(–12) mm (vs 20–25 × 18–20 mm), obovoid or cup-shaped (vs ovoid), glossy purplish black when ripe (vs pink); and styles not persistent or c. 2 mm (vs 4 mm). – Type: Philippines, Mindanao Island, Surigao del Norte Prov., Claver , in forests on ultramafic soils, c. 50 m elevation, 3 vii 2010 (fl), E. S. Fernando 2279 (holotype PNH!; isotypes LBC!, PUH!, SING!). Figures 1, 2 .

Small, glabrous tree, 3–5 m tall; stem 6–10 cm in diameter, branches spreading above. Twigs 4-winged when young, turning quadrangular with age; resinous, reddish brown. Leaves opposite, subsessile, deep red when young. Petiole slightly swollen, drying deep black,

1–2 mm long. Lamina ovate-oblong, rigidly and thickly coriaceous, base cordate, apex bluntly obtuse to rounded, margins entire, both surfaces epunctulate, 9.3–13.0 × 5.6–8.1 cm; secondary veins 15–18 pairs, thin, (9.0–) 10.7–11.4 mm apart, innermost intramarginal vein thin, (2.3–) 2.7–3.5 mm from the margin, outermost intramarginal vein 0.7–0.9 mm from the margin, very faint; both surfaces of the midrib deep black. Inflorescence (axillary–) terminal, (4.0–)6.0– 7.6 cm long, 4-winged. Ultimate branchlets in triads, flowers sessile. Flower buds goblet-shaped. Hypanthium goblet-shaped, greenish proximally, black (reddish distally when fresh), 3.8–6.0 × 2.0– 4.5 mm (hypanthium limb 2–3 mm, ovary portion 2–3 mm), rim with

4 rounded lobes, one pair larger than the other, 1.3–1.5 × 0.5–0.7 mm, pseudo-pedicel slender, 1.1–1.3 mm long. Corolla pseudo-calyptrate, white, 4-merous, irregular rounded. Stamens many, filaments slender, white, 8–10 mm long, anthers basifixed, broadly oblongsuborbicular, parallel, (yellow when fresh), 0.2–0.3 × 0.3–0.5 mm. Style 1, 7–10 mm long. Ovary bilocular, axile placentation; ovules c.15 per locule. Infructescence terminal. Fruits obovoid or cup-shaped, 7–8(–9) × 6–8(–12) mm, the surface smooth, hard, black (ripening glossy purplish black when fresh); distally ± flat with circular calyx rim (2.5–)3.0–4.0 mm wide, calyx lobes shallow, fleshy, weakly incurved, c. 1 mm long, style not persistent or when persistent c. 2 mm long. Seed 1, globose, testa smooth, 5–7 mm wide, (white to pinkish red when fresh), surface of the opposite facing cotyledons slightly undulate.

Seedling germination (fresh material): epigeal, phanerocotylar; hypocotyl c. 18–22 mm long, 1.0– 1.5 mm thick; epicotyl 8–21 mm long, 4-angular, the edges sometimes reddish; cotyledons of bulky or reserve type, planoconvex, smooth and rounded on the outside and covered with the brown testa; the exposed inner cotyledon green as is the emerging seedling axis, c. 2–3 mm thick, cotyledon stalk c. 1 mm long; first two eophylls opposite, lamina narrowly elliptic, 10–24 × 2–5 mm, base attenuate, apex acute; subsessile.

Distribution. This species is, thus far, restricted to the islands of Mindanao and Hinatuan. In Mindanao, it is known to occur only in Surigao del Norte Province.

Habitat and ecology. The type population of this species was found along a stream at

55–60 m elevation on ultramafic soils, although some individuals were also recorded at higher elevations reaching to 260 m. Other plant species in the type locality include Alyxia obovatifolia Merrill ( Apocynaceae ), Bikkia philippinensis Valeton ( Rubiaceae ), Buchanania insignis Blume ( Anacardiaceae ) and Rhodomyrtus surigaoensis Elmer ( Myrtaceae ).

Etymology. The epithet omissum (Latin for ‘neglected, disregarded’) alludes to the fact that although first encountered several years ago, this species has only recently been given attention.

Proposed IUCN conservation category. Using GeoCAT ( Bachman et al., 2011; https://www. geocat.kew.org), an extent of occurrence (EOO) of 196.5 km 2 was calculated, which is within the threshold for an Endangered category. The AOO was estimated at 32 km 2, which is also within the threshold for an Endangered category ( IUCN, 2012). This species has a severely fragmented population; known populations occur in small patches comprising a few individuals. After more than a decade of field visits to the area, we have observed a steady decline in the: (i) EOO; (ii) area of occupancy (AOO); and (iii) area, extent and quality of the habitat, and number of locations. All known localities of this species, including that on the small adjacent Hinatuan Island, are within areas subject to surface mining for nickel. Using the IUCN Red List Categories and Criteria ( IUCN, 2012) and the Guidelines for Using the IUCN Red List Categories and Criteria ( IUCN Standards and Petitions Subcommittee, 2022), we preliminarily assess Syzygium omissum as Endangered [EN B1+B2ab(i,ii,iii,iv,v)].

Notes. The combination of characters for this species is unique among all Philippine Syzygium . When Robinson’s (1909) key to Philippine species was used, the leaf characters and inflorescence position were found to closely resemble those of Syzygium bernardoi , but the stems and reproductive parts are very different (see diagnosis). Syzygium bernardoi was observed to have similarities to the Antisepticum group, whereas S. omissum is perhaps truly related to the Myrtifolium group of Robinson (1909), considering their small turbinate flowers, inconspicuous and small calyx lobes (i.e. hypanthium rim subtruncate), pseudo-calyptrate corolla, and ripe pericarp fleshy and purplish black. Syzygium silamense is not assigned to a group in Ashton (2006, 2011), and the holotype does not contain the material needed to enable this. The term ‘bulky or reserve type’ in Syzygium omissum refers to exposed cotyledons that are thick and ‘food-storing’, as opposed to foliaceous or leaf-like ( Ng, 1978; De Vogel, 1981) (see Figure 2E,F).

Additional specimens examined (paratypes). PHILIPPINES. Mindanao Island: Surigao del Norte Prov., Claver , along river, 53 m elevation, 8 viii 2013 (fr, seedling, + spirit), E. S. Fernando 3224 ( LBC!) ; ibid., along small, rocky stream, 55 m elevation, 23 iv 2015 (fl buds), E. S. Fernando 3759 ( CAHUP!, LBC!, PNH!) ; ibid., 260 m elevation, 7 vi 2019 (fl, fr), E. S. Fernando 4781 ( LBC!, PNH!, PUH!) ; ibid., 55 m elevation, 16 xii 2020 (fl buds, fr juvenile, fr, seedlings), E. S. Fernando 4968 ( LBC!) ; ibid., near nursery area, on gentle slope, 210 m elevation, 6 xi 2022 (fl, + spirit), E. S. Fernando 5224 ( LBC!) ; ibid., 114 m elevation, 20 vi 2023 (fr, seedling, + spirit), E. S. Fernando 5394 ( LBC!) . Hinatuan Island: 95 m elevation, 4 xii 2023 (st), E. S. Fernando 5670 ( LBC!) .