Rhizophora stylosa Griff.

Ngernsaengsaruay, Chatchai, Mianmit, Nittaya, Kamsanor, Supol, Pothitan, Rachanee, Jintana, Vipak, Jintana, Nirat, Chanton, Pichet, Sukantatul, Apinya & Khade, Jutiporn, 2025, Rhizophora stylosa (Rhizophoraceae) newly recorded from Thailand: lectotypification, leaf anatomy, and pollen morphology, PhytoKeys 259, pp. 1-25 : 1-25

Rhizophora stylosa Griff. , Not. Pl. Asiat. 4: 665. 1854; G. Hensl. in Hook. f., Fl. Brit. India 2: 436. 1878; Ridl., Fl. Malay Penins. 1: 693. 1922; Ding Hou, Fl. Males., Ser. 1, Spermat. 5 (4): 456, figs. 5, 8 a – f, 13. 1958 et Blumea 10 (2): 629. 1960; Backer & Bakh. f., Fl. Java 1: 380. 1963; Toml., J. Arnold Arbor. 59: 163, figs. 3, 4 D – F. 1978; N. C. Duke & J. S. Bunt, Aust. J. Bot. 27: 672. fig. 6 a – b. 1979; A. McCusker in A. S. George et al., Fl. Australia 22: 2. 1984; W. Giesen et al., Mangrove Guideb. S. E. Asia: 239, fig. 239. 2007; H. Qin & Boufford, Fl. China 13: 296, fig. 316 (1–9). 2007; N. C. Duke, Blumea 55: 179, fig. 8. 2010; A. D. Setyawan et al., Nusantara Bioscience 6 (1): 77, figs. 6 A. b – G. b, 8. 2014; Ragavan, Taxon. Mangroves Andaman and Nicobar Isl. PhD Thesis: 115, fig. 43. 2015; Ragavan et al., Indian Mangroves: 122–123. 2021; S. Kannan et al., Bot. Mar. 64 (3): 7–8, figs. 3 D, 5 B, D, F, G, J, L, M (right), O, 2021.

Figs 1 , 2 , 3 , 4 , 5

≡ Rhizophora mucronata Poir. var. stylosa (Griff.) A. Schimp. , Bot. Mitt. Tropen 3: 92. 1891; Guillaumin in Lecomte et al., Fl. Indo-Chine 2 (6): 724. 1920.

Type.

Peninsular Malaysia • Malacca (Melaka, Malay), s. d., W. Griffth s. n. (lectotype K digital image! [ K 005752944 ] (Fig. 5 A ), designated here; isolectotype: BR digital image! [ BR 0000031831338 ] (Fig. 5 B ).

Description.

Habit small evergreen trees, single- to multi-stemmed, 2.5–8 m tall, 10–60 cm GBH. Stilt roots much-branched, descending from the base of the stem, bearing numerous lenticels. Branches and branchlets decussate, growing upward at acute angles; branches often with pendulous aerial roots; branchlets terete, glabrous, with conspicuous annular stipular scars and leaf scars at the nodes. Bark grayish brown or dark brown, varies from smooth, rough or shallowly longitudinally and transversely fissured. Stipules interpetiolar, in pairs enclosing the young shoot (including the terminal bud and young leaves) and young inflorescences, pale green or green, turning whitish pale green or creamish white before the leaves emerging or before falling off, reddish brown when dry, linear-lanceolate, gradually narrowing towards the apex, 3.5–7.5 cm long, 2.5–9 mm diam. at the base, apex acute, glabrous and caducous, outline in transverse section depressed orbicular basally and suborbicular to orbicular apically, with dense colleters aggregated in a basal band, producing a sticky white exudate; colleters sessile, pale yellow, narrowly conical, 0.5–1.2 mm long, 0.2–0.5 mm diam. at the base, apex obtuse. Leaves decussate and crowded at the apical part of branchlets, elliptic, 8–16 × 3–8.5 cm, apex mucronate, a short terminal stiff point pale green, turning black before they come off, 2–6 mm long, base cuneate, margin entire, coriaceous, shiny dark green above, pale green below, glabrous on both surfaces, with numerous conspicuous, scattered tiny black cork warts below, midrib pale green (paler than lamina), flattened above, raised below, secondary veins 8–14 on each side, curving towards the margin and connected in distinct loops and united into an intramarginal vein, visible above, obscure below, with intersecondary veins, veinlets reticulate, visible above, obscure below; petioles green, 2–4.8 cm long, 2–4.5 mm diam., glabrous; fresh leaves brittle when crushed; young leaves shiny pale green; mature leaves turning greenish bright yellow and bright yellow before falling off; dry leaves yellowish brown. Inflorescences axillary, opposite, compound dichasia, dichotomously branched, 4–13 - flowered cymes, 5–12.5 cm long; peduncles pale green, 2.3–6 cm long, 2–3.5 mm diam., glabrous. Bracts 2, pale green, concave, 2.5–4 × 2.7–3.5 mm, apex rounded. Bracteoles at the base of the flower, pale green, connate at the base, bilobed, 3–5 × 4–6 mm. Flowers 4 - merous; flower buds pale green, turning pale yellow when mature, ovoid or conical-ovoid, 0.9–1.5 cm long, 4–8 mm diam., apex obtuse; fully open flowers 1.2–1.8 cm diam.; sepals 4, erect or patent after anthesis, pale yellow on both sides, triangular, 0.7–1.3 cm × 4–6 mm, apex acute, coriaceous, glabrous; petals 4, creamish white, narrowly elliptic or elliptic, 0.6–1 cm × 1.5–3.5 mm, thin, involute, densely long-villous along margins; stamens 8, 4 antesepalous and 4 antepetalous (each petal enclosing 1 stamen in flower buds); anthers falcate-like, 3.5–8.5 × 1.2–2.8 mm, apex mucronate, triangular in outline in transverse section; filaments very short; free part of the ovary 0.7–1.2 mm long, 1.2–1.8 mm diam.; style 3–5 mm long; stigma 2 - lobed; pedicels pale green, 0.6–1 cm long, 2–3 mm diam. Fruits brownish green, greenish brown or brown, ovoid or conical-ovoid, 2–2.7 cm long, 1–1.7 cm diam. at the base, apex obtuse (before seed germination); obpyriform, 2.2–4 cm long, 1.7–3 cm diam. at the basal part, 0.9–1.7 cm diam. at the apical part (when the hypocotyls nearly come off), roughened surface; persistent sepals reflexed, triangular, 0.9–1.1 cm × 5–8.5 mm; infructescence stalks 2–6 cm long, 2–3 mm diam.; fruit stalks 0.6–1.7 cm long, 3–5 mm diam. Seeds 1, viviparous. Hypocotyls green, slightly glossy, cylindrical-clavate, 19.5–40 cm long, 6.5–9 mm diam. at the apical part, 1–1.6 cm diam. at the widest part, 0.8–1.3 cm diam. at the basal part, acute at the basal end, roughened surface, with numerous, scattered lenticels; cotyledonous cylindrical tubes pale green or greenish pale yellow, 0.6–1.2 cm diam. (can be seen when the hypocotyls nearly falling off).

The measurements of the vegetative and reproductive parts of Rhizophora stylosa in Thailand are presented in Table 1 .

Distribution.

India (Andaman and Nicobar Islands), China (South Guangxi, South Guangdong, Hainan), Taiwan (Taipei), Japan (Ryukyu Islands, also known as Nansei-shoto), Vietnam, Cambodia, Peninsular Thailand, Peninsular Malaysia (also called Malaya), Singapore, Indonesia [Java, Lesser Sunda Islands, Sulawesi (also called Celebes), Moluccas (also called Maluku)], Philippines, Australia (Northern Territory, Queensland, New South Wales, Western Australia), Melanesia ( Bismarck Archipelago, New Guinea, Solomon Islands, Vanuatu, Fiji, New Caledonia), Micronesia ( Mariana Islands, Caroline Islands, Gilbert Islands), Polynesia ( Tuvalu, Tonga, Society Islands) (Fig. 6 ).

Distribution in Thailand.

Rhizophora stylosa is known only from Ko Lidi and Ko Bulon Le within Mu Ko Phetra National Park, located in La-ngu District, and from Ao Talo Wao, Ko Tarutao, in Tarutao National Park, Mueang Satun District, Satun Province, Peninsular Thailand (Fig. 6 ).

Habitat and ecology.

Rhizophora stylosa typically occurs along coastal areas with muddy-sandy, sandy or sandy-rocky substrates. This species is found at the seaward edge of mangrove forests and is well adapted to grow in open coastal environments, particularly along fairly exposed shores.

The populations of R. stylosa observed in Thailand are also located in low intertidal zones characterized by rocky and sandy substrates, similar to the observations reported from the Andaman and Nicobar Islands, India by Ragavan (2015) and Ragavan et al. (2021).

In the Andaman and Nicobar Islands, the species is uncommon and is mostly found in mangroves fringing the open coast, towards the seaward side. It is often found in mid to low intertidal zones and along downstream tidal creeks. The species grows in a variety of habitats, including disturbed mangrove areas. One distinctive niche is its ability to grow along the edges of small coral islands, where it establishes on coral substrates ( Ragavan 2015; Ragavan et al. 2021).

Phenology.

Flowering, fruiting and viviparous germination more than once, nearly throughout the year.

Conservation status.

Rhizophora stylosa is widely distributed, ranging from India (Andaman and Nicobar Islands) and China through Indo-China to the Pacific Islands. It is known from numerous localities, with a very large EOO of 52,723,897.41 km 2 and a relatively large AOO of 1,908 km 2. In Thailand, however, the species is restricted to Satun Province in the peninsular region, where it has a small EOO of 251.22 km 2 and a relatively small AOO of 12 km 2. Despite its limited national distribution, its broad global range, presence in numerous localities, and the absence of significant threats to its survival, we recommend a conservation assessment of Least Concern ( LC), in agreement with Ellison et al. (2010).

Etymology.

The specific epithet of Rhizophora stylosa is a Latin word that refers to its characteristic long style.

Vernacular name.

Kongkang phetra (โกงกางเภตรา) (suggested here); Red mangrove, Small stilted mangrove, Spotted mangrove, Stilted mangrove (English).

Uses.

To date, there has been no record of its use in Thailand. On Japan’s Iriomote Islands, the traditional dyeing of cotton fabric using tannins extracted from the bark of Rhizophora stylosa (Yaeyama hirugi), a technique known as kusaki-zome, remains an important cottage industry. The dye from the outer bark is brownish, while that from the inner bark is reddish ( Baba 2004; Baba et al. 2013). On Iriomote and Ishigaki Islands, seedlings of R. stylosa are sold in souvenir shops to tourists as ornamentals ( Baba et al. 2013). This species is utilized for timber, firewood, and the production of charcoal in the Pacific Island countries ( Giesen et al. 2007; Kainuma et al. 2015). In Australia, Aboriginal people use its wood to make boomerangs, spears, and ceremonial items ( Giesen et al. 2007).

Lectotypification.

Rhizophora stylosa was named by Griffith (1854: 665), who cited only the type locality “ Hab. Malacca, in littoribus limosis, Pulo Bissar ”. However, he did not designate a holotype, nor did he provide a collector number or indicate the herbarium where the material was housed. We have located the specimen W. Griffth s. n. from Malacca at K [ K 005752944] and BR [ BR 0000031831338], which following Art. 9.6 of the ICN ( Turland et al. 2018), must be considered syntypes. William Griffith (1810–1845) was a British colonial physician and botanist who made substantial contributions to the herbarium of the East India Company. His herbarium was originally deposited at LINN, but was later transferred to Kew ( K), with significant duplicate specimens housed at BR and CAL ( Stafleu and Cowan 1976). Accordingly, we designate the specimen at K [ K 005752944] as the lectotype, with the specimen at BR [ BR 0000031831338] being an isolectotype, in accordance with Arts. 9.3 and 9.12 of the ICN ( Turland et al. 2018).

Notes.

The colors and sizes of the stipules of Rhizophora stylosa are pale green or green, turning whitish pale green or creamish white before falling off. They are 3.5–7.5 cm long, 2.5–9 mm diam. at the base. In contrast, the stipules of R. mucronata are pale green, reddish pale green, or pale greenish red when young, turning pale yellow or reddish pale yellow before falling off, and are larger, 4.5–12.5 cm in length and 0.5–1.7 cm in diameter at the base. The petioles, peduncles, rachises of inflorescences, and pedicels of R. stylosa are usually terete, whereas those of R. mucronata are slightly to somewhat flattened.

Morphologically, R. stylosa is closely related to R. mucronata (Fig. 7 ) in its inflorescences and flowers (including flower buds, pedicelled flowers, bracteoles, sepals, and stamens); in the length of the stiff, pointed leaf tips; in the shape and basal diameter of the fruits (when the hypocotyls nearly come off); in the shape and color of the hypocotyls; and in the colors of the cotyledonous cylindrical tubes and colleters. The differences between these two Thai species of Rhizophora are presented in Table 2 .

Two distinct populations of R. stylosa were found in Mu Ko Phetra National Park, La-ngu District, Satun Province, Peninsular Thailand. Population A is distributed along coastal areas characterized by muddy-sandy substrates, predominantly occupying the seaward edge of the mangrove forest at Ko Lidi, La-ngu Subdistrict. In contrast, Population B occurs along coastal areas with sandy to sandy-rocky substrates, particularly along relatively exposed shorelines at Ko Bulon Le, Pak Nam Subdistrict. Morphological comparisons between the two populations reveal that individuals in Population A (3–8 m) tend to be taller than those in Population B (2.5–5 m). Furthermore, vegetative and reproductive structures, including stipules, leaves, petioles, inflorescences, peduncles, and fruits, are generally larger in Population A. These morphological differences are likely influenced by environmental conditions, suggesting that substrate type and coastal exposure play significant roles in shaping the growth and reproductive traits of R. stylosa in this region (Table 3 ).

Additional specimens examined.

Thailand. Peninsular: • Satun [Ko Lidi, Mu Ko Phetra National Park, La-ngu Subdistrict, La-ngu District , fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. Rs 01-22042025 ( BKF); • Ao Phangka, Ko Bulon Le, Mu Ko Phetra National Park, Pak Nam Subdistrict , La-ngu District , fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. Rs 02-22042025 ( BKF); • ibid., fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. Rs 03-22042025 ( BKF) ; Ao Talo Wao, Ko Tarutao, Tarutao National Park, Mueang Satun District , fl., 30 May 2025, N. Mianmit & N. Kaveethanathum personal observation with photos ; Note. C. Ngernsaengsaruay et al. = C. Ngernsaengsaruay, N. Mianmit, R. Pothitan, V. Jintana, N. Jintana & S. Kamsanor].

Figures

Figure 1. Rhizophora stylosa. A, B. Flowering branchlets showing a terminal interpetiolar stipule, leaves, and inflorescences with flower buds and fully open flowers; C. Flower buds; D. Flower bud in transverse section; E. Fully open flower in lateral view; F. Fully open flower in top view; G. Flower bud showing stamens with sepals and petals removed; H. Flower bud in longitudinal section; I. Sepals; J. Petals with densely long-villous along margins; K. Stamen; L – M. Pistils showing a long style; N – O. Fruits showing successive stages in development of hypocotyl. Drawn by Wanwisa Bhuchaisri.

Figure 2. Rhizophora stylosa. A – D. Habitats and habit; E. Stems supported by numerous branched stilt roots; F. Stem, outer bark and inner bark; G. Leaves showing adaxial and abaxial surfaces: Population A (left) and Population B (right); H. Branchlets, leaves and young inflorescences; I. Leaf scar with many tiny vascular bundle strands, arranged in a crescent moon; J. Stipule with dense colleters aggregated in a basal band, producing a sticky white exudate. Photos: Chatchai Ngernsaengsaruay (A – C, E – J) and Rachanee Pothitan (D).

Figure 3. Rhizophora stylosa. A, B. Flowering branchlets showing inflorescences with flower buds and fully open flowers; C. Flowering branchlets showing flower buds and fully open flowers and fruiting branchlet showing young fruits; D. Inflorescence with flower buds and fully open flower; E, G. Flowering and fruiting branchlets showing leaves, inflorescences with flower buds and fully open flowers, and hypocotyls. F. Seedling. Photos: Chatchai Ngernsaengsaruay.

Figure 4. Rhizophora stylosa. A. Fully open flower; B. Flower bud in longitudinal section; C. Flower bud in transverse section; D. Dissected flower showing sepals, petals, stamens, and pistil; E – G. Sepals; H – J. Petals with densely long-villous along margins; K – N. Stamens; O. Pistil showing a long style. Photos: Pichet Chanton (A – N), Apinya Sukantatul (O).

Figure 5. Lectotype and isolectotype of Rhizophora stylosa from Malacca, Peninsular Malaysia. A. Lectotype, W. Griffth s. n. (K [K 005752944]); B. Isolectotype, W. Griffth s. n. (BR [BR 0000031831338]). Photos: © The Board of Trustees of the RBG, Kew, https://records.data.kew.org/occurrences/f573f797-57cc-48c7-b444-c6a9b8f085c3 (A), Meise Botanic Garden, Meise, Belgium, https://www.botanicalcollections.be/specimen/BR0000031831338 (B).

Figure 6. Distribution of Rhizophora stylosa. It is widely distributed from India (Andaman and Nicobar Islands), China to Indo-China, and the Pacific Islands. In Thailand, this species is known only from Ko Lidi and Ko Bulon Le within Mu Ko Phetra National Park, located in La-ngu District, and from Ao Talo Wao, Ko Tarutao, in Tarutao National Park, Mueang Satun District, Satun Province. Map: Pichet Chonton & Chatchai Ngernsaengsaruay.

Figure 7. Rhizophora mucronata. A. Branchlets, leaves and terminal interpetiolar stipule; B. Leaves showing adaxial and abaxial surfaces; C. Flowering branchlet showing inflorescences with flower buds and fully open flower; D. Petal with densely and shorter villous along margins; E. Flower bud in longitudinal section showing very short style; F. Fruiting branchlet showing leaves and mature fruit with persistent sepals; G, H. Fruiting branchlets showing leaves and successive stages in development of hypocotyl. Photos: Chatchai Ngernsaengsaruay (A – C, F – H), Pichet Chonton (D, E).