Syzygium setosum (King) I.M. Turner

Mustaqim, Wendy A., Randi, Agusti, Wijedasa, Lahiru S., Widodo, Pudji, Rivers, Malin, Lucas, Eve & Low, Yee Wen, 2023, Syzygium setosum (Myrtaceae), a rare and endangered peat swamp tree in Southeast Asia: lectotypification, conservation status and a new record in Sumatra, Candollea 78 (2), pp. 153-159 : 153-159

Syzygium setosum (King) I.M. Turner in J. Singapore Natl. Acad. Sci. 22–24: 24. 1997 (F ig. 1).

÷ Eugenia setosa King in J. Asiat. Soc. Bengal, Pt. 2, Nat. Hist. 70: 120. 1901.

Lectotypus (designated here): MALAYSIA. Perak: Taiping, VIII.1888, Wray 2704 ( G [ G00415921 ] image!; isolecto-: K [K000800015]!, SING [SING0056121]!).

Syntypi: MALAYSIA. Perak: Larut, c. 90 m, XII.1883, King’s Collector (Kunstler) 5266 ( BM [ BM 000944152] image!, K [ K 000800016]!, P [ P 05209634] image!, SING [ SING0056122 ]!, U [U.1439009] image!); Larut, c. 30 m, IX.1884, King’s Collector (Kunstler) 6601 ( A [ A 0 0 0 6 9 5 6 3], G [ G 0 0 4 1 5 9 2 2] i m a g e!, GH [ GH 00069564] image!, K [ K 000800017]!); Larut, c. 90 m, XI.1884, King’s Collector (Kunstler) 6793 ( K!, L [L.2515508] image!, P [ P 05209633] image!).

Small tree, to 10 m high, trunk to c. 6 cm diam., buttresses short to 5 cm high or absent, without stilt roots. Bark smooth with scattered lenticels, dark reddish-brown; inner bark pale cream; sapwood pale to dark cream. Twigs 1.5–3 mm across, covered with reddish-brown erect bristly hairs; internodes 1.5 – 4.5 cm long, straight. Petioles 1.5 – 3 mm long, sparsely covered with short erect hairs. Leaves lamina elliptic to oblong, 3.5–8.5 × 0.9–3.5 cm, lower surfaces punctate; base rounded to cordate; apex caudate, margins slightly revolute; midrib sunken and glabrous on the upper surface, prominent and sparsely hairy on lower surface; primary secondary veins 26–35 pairs, basal most veins nearly perpendicular, otherwise upward diverging at c. 75° from the midrib; intercostal veins less distinct from primary secondary veins, forming somewhat inconspicuous veins at the upper quarter; intramarginal veins 1, 0.5–1 mm from the margin, hardly looped. Inflorescences a paniculate cyme of numerous flowers, terminal and in the upper axils, solitary or up to 3 in the apex of a leafy twig; rachis 4–10 cm long, covered with coarse and wiry erect hairs, white at first, turning reddish-brown during anthesis; floral bracts triangular, c. 0.5 mm long, acute. Ħlowers 5-merous, buds clavate, obconical, c. 5 mm long, c. 3 mm wide. Hypanthium obconical, c. 2.5 mm long, outer surface tuberculate without hairs, tapering abruptly to c. 1 mm long pseudostalk. Calyx lobes 5, triangular, c. 0.1 mm long, apex pointed, persistent after anthesis. Petals 5, likely somewhat cohered together and falling off as a pseudocalyptra, c. 2 mm across. Stamens c. 22; filaments 2–4 mm long, white; anthers broadly oblong, c. 0.4 mm long, cream (fide HENDERSON, 1949). Style cylindrical, gradually narrowed from the base towards the apex, 4– 5 mm long, white. Ħruits subglobose to nearly globose, c. 1.8 × 2.2 cm, maturing from green to yellowish-green when ripe, shallowly excavated at the apex and sometimes with remnants of the calyx lobes; mesocarp light green, becoming white inwards. Seeds solitary, cotyledonary intrusion absent.

Distribution and ecology. – Peninsular Malaysia (Perak and Selangor), Malaysia, and Sumatra (Sumatra Utara and Sumatra Selatan Provinces) (F ig. 2). Syzygium setosum occurs in lowland peat swamp forests up to c. 90 m. In Sumatra Selatan Province it is commonly found in primary peat swamp forests that are constantly wet and flooded periodically ( Randi GB-052). In Peninsular Malaysia, S. setosum can also occur in regenerated degraded peat swamps (Chew & Mohd. Nazri ĦRI78690).

Conservation status. – Syzygium setosum is a rare obligate peat swamp forest tree restricted to Peninsular Malaysia ( Malaysia) and Sumatra ( Indonesia ). So far, this taxon is known from 16 herbarium specimens, 13 of which were made between the late 19th century to the mid-20th century. Based on these collections, the species extent of occurrence (EOO) is estimated to be 138, 373 km ², and its area of occupancy (AOO) is estimated to be 48 km ². The primary conservation concern for the species is habitat loss linked to human activities such as agricultural exploitation, logging, rapid expansion of urban areas and forest fire, which have increased significantly since the 1960s. Degraded peat lands caused by human activities are prone to forest fires and the effects of climate change further exacerbated its intensity and occurrence as seen in the region in recent years (HUIJNEN et al., 2016; BUDININGSIH et al., 2022). Due to rapid land use change, the area of peat swamp forest in Southeast Asia declined between 1990 and 2015 from 76 % to 29 % of the area (a loss of 4.6 Mha), with a corresponding increase of 11 % to 50 % in agricultural area (MIETTINEN et al., 2017), comprising both small-scale farms and large-scale industrial plantations ( POULTER et al., 2021). Of the remaining peat swamp forest, only 42 % is in official protected areas (WIJEDASA et al., 2018). Due to this decline in peat swamp forests, many historical localities of S. setosum are now lost. Analyses show that for this species, the EOO and AOO have declined by more than 50 % in the last three generations (c. 15 years for three generations according to LOW et al., 2022), and the loss of peat forest is ongoing and therefore population decline is suspected to also be continuing. Therefore, considering this population decline, and that the taxon now only exists in fewer than five locations, the AOO is less than 500 km ² and there a continuing decline in habitat (as supported by the Global F orest Watch data [https://www. globalforestwatch.org]), and loss of several subpopulations, S. setosum should thus be assigned a conservation status of “Endangered” [EN A2c+4c; B2ab(iii,iv)] based on IUCN Red List categories and criteria ( IUCN, 2012) and guidelines (IUCN, 2022). This conservation status may require reassessment as more botanical surveys in Peninsular Malaysia and Sumatra are being carried out.

Notes – Eugenia setosa was described by George King in 1901 based on four collections, namely Wray 2704ư King’s Collector (Kunstler) 5266ư 6601ư and 6793, from Perak in Peninsular Malaysia (KING, 1901). HENDERSON (1949) expanded the taxon distribution to include Selangor based on two collections, Mohd. Nur SĦN34068 and Symington ĦMS44033. Later, TURNER (1997) transferred E. setosa to Syzygiumư following other regional studies accepting SCHMID’S (1972) proposal to recognise Syzygium as distinct from Eugenia s.s. Amongst all known Malayan Syzygium , S. setosum is characteristic in having reddish-brown erect bristly hairs on the twigs and inflorescence axis, paniculate inflorescences, lamina with rounded to subcordate bases, numerous secondary nerves (26–35 pairs) and small flowers (c. 5 × 3 mm).

Other reddish hairy West Malesian Syzygium species include S. fulvotomentosum P.S. Ashton, S. hirtum (Korth.) Merr. & L.M. Perry , and S. villiferum (Ridl.) Masam. However, only S. hirtum has erect bristly hairs similar to S. setosum , while both S. fulvotomentosum and S. villiferum have velvety downy hairs. Syzygium fulvotomentosum is a northern Borneo endemic, and differs from S. setosum in having a petiole up to 10 mm long (vs. up to 3 mm long in S. setosum ), cuneate leaf bases (vs. rounded to cordate in S. setosum ), and flowers up to 10 mm long (vs. up to 4 mm long in S. setosum ). Both S. hirtum and S. villiferum occur in Sumatra and Borneo. The latter differs from S. setosum in its larger leaves (c. 24–38 × 6.5–14 cm) and flowers (c. 12 × 7 mm), while the former differs from S. setosum in having fewer lateral nerves (c. 25 pairs) and larger flowers (c. 15 × 8 mm).

Neither HENDERSON (1949) or TURNER (1997) designated a lectotype for this name. Among the four syntypes cited in the protologue, we designate the most informative specimen, Wray 2704 at G, as the lectotype. It is worth noting that King’s Collector (Kunstler) 6601 at K was annotated anonymously with the number “2” above the number “1”, giving the impression of being numbered “6602” instead of “6601”. Otherwise, the label information is identical to in the other duplicates deposited at A, G, and GH. In SING, two specimens numbered King’s Collector 6602 are identified as Dacryodes incurvata ( Burseraceae ).

The purported habit of Syzygium setosum was originally described as a shrub or creeper according to the label information of some specimens (e.g. King’s Collector (Kunstler) 5266, 6793). Based on the herbarium specimens and living plants examined, in Sumatra this species rather corresponds to a tree. A woody plant species may exhibit different growth habits in a highly humid environments, such as freshwater swamp forests, peat swamp forests or montane (mossy) forests. As the specimens described as “creeping” lack the morphological characteristics of a typical climber, such as hooks, tendrils, sticky pads, twining stems and stem roots, it is likely that the collector came across individuals behaving atypically in a very humid environment in the swamps. Additional studies are needed to clarify this issue.

Additional specimens examined. – INDONESIA. Prov. Sumatra Selatan: Sungai Lalang Petaling , 11.XII.1979, Anon. TĦB357 ( L [ L.2515506 ] image!); Musi Banyuasin Regency , Bayung Lencir Distr., Muara Medak village, conservation area of PT Tri Pupajaya forest production concession, 1°46'15"S 104°12'07"E, 10 m, 30.XI.2020, Randi GB-052 ( BO). Prov. Sumatra Utara: Tebing Tinggi, 25.VIII.1918, Bruinier 76 ( L [ L.2515507 ] image!); Labuhan Batu , Labuhan Bilik, 17.X.1928, Lörzing 14275 ( L [L.2515504] image!) .

MALAYSIA. Perak: Larut, c. 90 m, I.1884, King’s Collector (Kunstler) 5447 ( SING [ SING 0352109]); Larut, c. 90 m, VI.1884, King’s Collector (Kunstler) 6202 ( M [ M 0171111], SING [ SING 0352111]); Hilir Perak , Hutan Melintang F orest Reserve, Compartment 11, 13.IX. 1967, Ng ĦRI5696 ( K, KEP [ KEP 99003]); Telok Anson , Changkat Jong , Sungai Hidup, 17.II.1975, Mohd Shah & Mahmud MS3463 ( KEP [ KEP 5678], SING [ SING 0152144]) . Selangor: Kuala Selangor , Sungai Tinggi (Sungai Tengi), 8.5th mile, 19.VII.1937, Symington ĦMS44003 ( KEP [ KEP 99005]); Kuala Selangor , Sungai Tinggi (Sungai Tengi), 13.X.1937, Md. Nur SĦN34068 ( KEP [ KEP 99004], L [L.2515509], SING [ SING 0352110]); Kuala Selangor , Sungai Karang F orest Reserve, NSPS F Expedition, Trail 6, 3°40'34"N 101°11'05"E, 23 m, 1.VII.2013, Lim & Mohd. Nazri ĦRI72900 ( K, KEP [ KEP 238582]); Kuala Selangor , Tanjung Karang, off Trail 4, 3°31'20"N 101°10'37"E, 25 m, 4.VII.2013, Chew & Mohd. Nazri ĦRI78690 ( K, KEP [ KEP 233315], SING [ SING 0215314]!) .