Bruguiera gymnorhiza

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 : 44-45

2. Bruguiera gymnorhiza (L.) Savigny — Fig. 2 ; Map 1

Etymology. ‘Gymno-rhiza’ means ‘naked root’ (in Greek),and refers to the conspicuous exposed knee roots of this species. Common name is ‘large-leafed orange mangrove’ in Australia.There has been confusion regards the spelling of ‘gymnorhiza’. The epithet was published by Linnaeus with one ‘r’ and quoted by Savigny in Lamarck & Poiret (1798) with one ‘r’ as well. However,more recent authors have used double ‘r’, such as Ding Hou (1958), Tomlinson (1986) and Wagner et al. (1990). Based on such usage, two ‘r’s are used by the ITIS data being derived from the USDA PLANTS database. The decision to make the change to one ‘r’ was based on the International Code for Botanical Nomenclature which states that the original spelling is to be used unless it has an error of a type that ought to be corrected, like the spelling.The question of one ‘r’ or two therefore depends on the Greek term from which this epithet was derived.Some recent authors had taken the view that this derivative used a double ‘r’, so Linnaeus’ spelling was corrected. However, others like the APNI, had taken a conservative view.A high-level working group of plant taxonomists representing all key Australian Herbaria (unpublished minutes, 17 October 2005) have justified retention of Linnaeus’ original spelling, following Stearn (1992) p. 261, who specifically discusses the case of ‘-rhiza’ in Greek compounds, and concludes that either spelling is equally acceptable.

Tree or shrub to 25 m, evergreen, columnar or multi-stemmed, branching mostly sympodial, stem base with spreading sinuous, stocky buttresses to 0.5 m high. Exposed root stilts rarely on lower stem, pneumatophores thick knee-like, to 30 cm. Bark dark grey-brown to black, rough, friable, predominately horizontal fissures, with large corky lenticels of ± 2 cm diam, especially on buttresses. Foliage comprised of compact rosettes of paired leaves, clustered at 4 – 9 leaf scar nodes around apical shoot, terminal, spicate, prominent, red-green, 3 –7 cm long. Interpetiolar stipules paired, lanceolate, often reddish or green to yellowish, enclose terminal bud to 7 cm long. Leaves opposite, simple, blade elliptic-oblong, coriaceous, glossy green, (8–)9 –19(–24) cm long, (3–)4– 8(–9) cm wide, (4–)5 – 9(–12) cm shape length, length/width ratio 1.9 – 2.8, length/shape ratio 1.9 – 2.4, with longitudinal folds, margin entire, apex bluntly pointed, base cuneate; petiole green, to 2– 5 cm long, often glaucous with white waxy coating. Inflorescence axillary, 1-flowered, buds generally nodding, maturing within leafy rosette; peduncle green, (8.7–)10–20(– 23) mm long, 2– 3.3 mm wide; mature buds present at 1–2 internodal segments below apical shoot; mature hypocotyls present at 4– 6 internodal segments below apical shoot. Mature flower buds bright red, occasionally yellowish green, 29 – 44 mm long, 4.5 –18 mm wide around calyx tube, 8.5 –14 mm at sepal lobes, distil tip acute; calyx tube turbinate, grooved or smooth, with 9 –15 lobes, slender, pointed, longer than tube, 17–26 mm long, margins on closed bud indented to smooth; petals 9 –15, creamy white, turning orange brown at anthesis, 12– 20 mm long, 1.8 – 3.1 mm closed width, bilateral folded, 3.5 – 5.7 mm open width, bilobed; lobes 2.3 –8.1 mm long, densely fringed with hairs along outer margins, apices acute with 2 – 3 bristles, 2– 4 mm long, sinus between lobes with hair-like spine, 2.5 –7.3 mm long, often exceeding lobes, spine/petal lobe length ratio 0.5–1.5; stamens 18– 30, creamy white turning orange brown at anthesis, 10–18 mm long, ± 0.5 mm wide, compressed pair within closed petal, dehiscing precociously when triggered, anthers linear, creamy pale yellow turning brown at anthesis, 4.1–7.9 mm long, ± 0.8 mm wide; style filiform, smooth, pale green, 16– 26 mm long, to 0.9 – 2 mm wide, stigma minutely 3– 4-lobed at tip, mounted centrally within calyx bowl 2.9 –6 mm wide, 4.2 –7.8 mm deep. Mature fruit cryptic within slightly enlarged calyx tube, turbinate, smooth to grooved, 37– 49 mm long, 6.8 –23 mm wide, lobes slightly reflexed, if at all, 16–23 mm long, 18– 38 mm spread width; germination viviparous, hypocotyl emergent from calyx with maturation. Mature hypocotyl cigar-shaped, straight, green, 7–22 cm long, 6 –22 mm at widest point, 39–93 mm shape length, 4–17 mm width at plumule end, length /width ratio 5.9 –14.7, length/shape ratio 1.6 – 2.8, longitudinal ribbing, distil end blunt, plumule 1.7– 4.3 mm long, buoyant dispersal agent.

Phenology — In the southern hemisphere, flowering peaks through April to August, and maturation of propagules occurs in January and February. This is expected to differ by six months in the northern hemisphere.

Ecology and local influences — A distinctive and common member of the mid-high intertidal mangrove community, occurring in downstream-intermediate estuarine positions. The species is found in a wide variety of habitat conditions ranging from deep estuarine muds, to sandy beaches, to coral and rocky coastal shorelines. As with other Bruguiera , this species has a distinctive explosive pollen release mechanism. Honey-eaters frequently visit the flowers to gather nectar.

Distribution — One of the most widely-distributed mangrove species, based on its broad longitudinal range in the Indo West Pacific region. The species is found from East Africa through India and the Malay Peninsula to South China, the Ryukyu Islands, Polynesia to Samoa and northern Australia. In Australia (Duke 2006), it occurs in most estuaries along the northern coast from Darwin Harbour, Northern Territory (12°25' S, 130°48' E) in the west, across Queensland, to Moonee Creek, New South Wales (30°13' S, 153°10' E) in the east.

Note — Bruguiera gymnorhiza is distinguished by its open flowers showing petals with 3 longish bristles at lobe tips. Bruguiera gymnorhiza is notably distinguished from other Bruguiera by a number of characteristics: – large, single-flowered inflorescences with petals having a spine roughly the same length as the paired lobes, as distinct from much longer spines of B. cylindrica , B. hainesii and B. parviflora ; and, its acute petal lobes with 3– 4 bristles, being distinct from the more rounded petal lobes and fewer bristles of B. sexangula , B. × rhynchopetala and B. exaristata . The calyces of B. gymnorhiza are often also distinctly bright red, almost scarlet in colour, but not always. Some trees have pale yellowish green coloured calyces, and no red ones. Trees with either red or green colour sometimes occur in mixed stands, like those in Great Sandy Strait and Fraser Island in Queensland, Australia. These same colour morphs occur in other locations, like Yap Islands in Micronesia. Another kind of colour variant is found in New Caledonia. In southern estuaries of this large Pacific island, there are many individual trees with much darker appearance than adjacent, normal ‘green’ trees. Darker trees appear to have red coloration throughout causing leaves and stems that might otherwise be green, to appear dark brown or dark green. Reproductive parts and apical shoots appear bright red. In each case, no corresponding morphological differences could be found to justify separate taxonomic determination.

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. 2 Bruguiera gymnorhiza (L.) Savigny. a. Habit,Hainan, China; b. tree, Solomon Islands; c bark;d. trunk and exposed roots;e. foliage with inflorescences; f. leafy rosette with open flower bud; g. closed mature flower bud; h. mature flower buds of two colour morphs – red and green; i. open flower bud showing petals; j. closed and open petals; k. diagram of open petal; l. mature hypocotyl. — Scale bars: a–k = 10 mm.