Bruguiera exaristata Ding Hou

Duke, N. C. & Ge, X. - J., 2011, Bruguiera (Rhizophoraceae) in the Indo-West Pacific: a morphometric assessment of hybridization within single-flowered taxa, Blumea 56 (1), pp. 36-48 : 41-44

1. Bruguiera exaristata Ding Hou — Fig. 1 ; Map 1

Etymology. ‘ex-aristata’ means ‘without a long bristle-like tip’ (in Latin), and refers to the absence of long hairs on petal lobes, and absence of a filamentous spine between petal lobes in this species. Common name is ‘rib-fruited orange mangrove’ ( Australia).

Tree or shrub to 10 m, evergreen, columnar or multi-stemmed, branching mostly sympodial, stem base with spreading, somewhat sinuous, stocky buttresses to 0.3 m high. Exposed root stilts rare, pneumatophores knee-like, thick, to 15 cm. Bark dark grey-brown to black, smooth to rough, friable, horizontal fissures, occasional corky lenticels ± 1 cm diam. Foliage comprised of compact rosettes of paired leaves, clustered at 6 –9 leaf scar nodes down from apical shoot, terminal, spicate, prominent, green, 2 – 4 cm long. Interpetiolar stipules paired, lanceolate, green to yellowish, enclose terminal bud to 4 cm long. Leaves opposite, simple, obovate, smooth, glossy green, (5–)6– 11(–12) cm long, (2–) 3 –5 cm wide, (3–)4– 6(–7) cm shape length (length from widest width to petiole juncture), length/ width ratio 1.9– 2.2, length /shape ratio 1.8 –1.9, often with longitudinal folds, margins entire, acute apex, base cuneate; petiole green, to 1–3 cm long. Inflorescence axillary, 1-flowered, buds generally nodding, maturing within leafy rosette; peduncle green to (7.9 –)8.1–11(–14) mm long, 1.5 –2(–2.3) mm wide; mature buds present at 1–2 internodal segments below apical shoot; mature hypocotyls present at 4 –5 internodal segments below apical shoot. Mature flower buds yellowish green, 22–28 mm long, 3.6 – 4.7 mm width around calyx tube, 6.3–7.9 mm width at sepal lobes, distil tip rounded; calyx tube turbinate, ribbed, with 9 –11 lobes, slender pointed, longer than tube, 12–14 mm long, margins on closed bud raised; petals 9–10, creamy white, turning orange brown at anthesis, 9 –13 mm long, 1.8 – 2.3 mm closed width, bilateral folded, 3.3 – 4.5 mm open width, bilobed; lobes 2.4– 3.8 mm long, densely fringed with hairs along outer margins, apices rounded, sometimes with a minute bristle to 0.2 mm long, often absent, sinus between lobes occasionally with minute spine to 0.4 mm long, often absent; spine /petal lobe length ratio 0 – 0.1; stamens 18–20, creamy white turning orange brown at anthesis, 9.3 –12 mm long, ± 0.3 mm wide, compressed pair within closed petal, dehiscing precociously when triggered, anthers linear, creamy pale yellow turning brown at anthesis, 4.2–5.4 long, ± 0.6 mm wide; style filiform, smooth, pale green, 13–17 mm long, to 0.7–0.9 mm wide, stigma minutely 3 –4-lobed at tip, mounted centrally within calyx bowl 2.5 – 3.6 mm wide, 2.9– 3.8 mm deep. Mature fruit cryptic within slightly enlarged calyx tube, turbinate, ribbed, ± 27 mm long, 6.1–12 mm wide, lobes usually reflexed, 10–12 mm long, 15– 22 mm spread width; germination viviparous, hypocotyl emergent from calyx with maturation. Mature hypocotyl finger-like, slender, straight, green, 8.6–10 cm long, 9 –10 mm at widest point, 31–37 mm shape length (length from widest point to distil end), ± 3 mm wide at plumule end, length /width ratio 9 –10.5, length/shape ratio 2.6– 3.2, slight longitudinal ribbing, distil end blunt, plumule 1–1.8 mm long, buoyant dispersal agent.

Phenology — In the southern hemisphere, notably Australia, flowering peaks during September and October, and propagule maturation occurs during February and March.

Ecology and local influences — Common constituent of the upper intertidal mangrove zone and intermediate-upstream estuarine position. In Australia, the species is found in a variety of habitats ranging from tidal backwaters, to stunted stands bordering saltpans and sandy beaches. Common associates include Ceriops australis and Xylocarpus moluccensis . As with other Bruguiera , this species has a distinctive explosive pollen release mechanism. Honey-eaters frequently visit the flowers to gather nectar.

Distribution — Distributed from eastern Indonesia, Timor and southern New Guinea to northern Australia. In Australia (Duke 2006), the species occurs in estuaries across the north coast from the Montebello Islands and Cossack, Western Australia (20°40' S, 117°12' E) in the west, across the Northern Territory, to Port Curtis, Queensland (23°49' S, 151°22' E) in the east.

Note — Bruguiera exaristata is readily recognised by its buttressed trunk, knee-like pneumatophores, opposite glossy green leaves, and moderately-large mostly solitary flowers with 8–10 lobes. The calyces are notable for their light green colour and distinctive ribbing. The species is distinguished from other single flower Bruguiera by the absence of an appreciable spine between petal lobes, and the absence of bristles on petal lobes.

Figures

Map 1 Global distributions of the three large, single-flowered Bruguiera species, B. exaristata, B. gymnorhiza and B. sexangula. Note that B. sexangula was introduced to the Hawaiian islands (Allen et al. 2000).

Fig. 1 Bruguiera exaristata Ding Hou. a. Habit, Darwin, Australia; b. bark; c. trunk and exposed roots; d. foliage; e. leafy rosette with mature buds; f. leaves; g. flower buds from immature to mature and open; h. open mature flower bud showing petals; i. closed and open petals; j. diagram of open petal; k. mature hypocotyl. — Scale bars: a–j = 10 mm.