Research Article |
Corresponding author: P. Ragavan ( van.ragavan@gmail.com ) Academic editor: Geoffrey Levin
© 2015 P. Ragavan, P.M. Mohan, R.S.C. Jayaraj, K. Ravichandran, S. Saravanan.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ragavan P, Mohan PM, Jayaraj RSC, Ravichandran K, Saravanan S (2015) Rhizophora mucronata var. alokii – a new variety of mangrove species from the Andaman and Nicobar Islands, India (Rhizophoraceae). PhytoKeys 52: 95-103. https://doi.org/10.3897/phytokeys.52.5037
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Rhizophora mucronata var. alokii (Rhizophoraceae), a new variety of Rhizophora from the Andaman and Nicobar Islands, India, is described and illustrated. The new variety is remarkable in having four stamens, laterally folded leaves, a short peduncle, thick leathery petals, and a four-sided ovary with a sessile style. A key for the species of Rhizophora of the Andaman and Nicobar Islands is also provided.
Rhizophoraceae , Rhizophora mucronata var. alokii , new variety, Andaman and Nicobar Islands, India
The genus Rhizophora is the most common mangrove genus worldwide. Two species (R. mangle L. and R. racemosa G. Mey) and one natural hybrid (R. × harrisonii Leechm.) are restricted to the Atlantic-East Pacific Region, three species (R. apiculata Blume, R. mucronata Lam., and R. stylosa Griff.) and four named natural hybrids (R. × annamalayana Kathiresan, R. × lamarckii Montrouz, R. × selala (Salvoza) Toml., and R. × tomlinsonii Duke) are restricted to the Indo-West Pacific (IWP) region, and one species (R. samoensis (Hochr.) Salvosal) extends into both regions (
The mangroves of the Andaman and Nicobar Islands (ANI) are denser and more diverse compared to other mangrove habitats in India (
During a recent botanical excursion, an interesting population of Rhizophora was encountered in the mangrove forest of Austin Creek, North Andaman. Specimens were collected and did not match any of the known species of the genus and hence have been described and illustrated here as new.
To better assess the taxonomic placement and distinguishing characteristics of the new taxon, a morphometric analysis of the Rhizophora taxa present in ANI was performed. Seventeen attributes of leaves, inflorescences and flowers (Table
Characters used for classification analysis of Rhizophora species of the ANI; average value (range) in cm for each taxon. Where no range is included, the values for the taxon showed no variation. Values that differ significantly (p < 0.05) between the varieties of R. mucronata are marked with an asterisk.
Characters | R. apiculata | R. mucronata var. mucronata | R. mucronata var. alokii | R. stylosa | R. × annamalayana | R. × lamarckii |
---|---|---|---|---|---|---|
Leaf length | 13 (8.5–16.2) |
13.55* (8.5–18) |
11.29* (7–13) |
11.1 (8–13) |
12.39 (10–16) |
13.08 (8–16) |
Leaf width | 5.9 (4–8.5) |
8.47 (5.7–11.3) |
6.71 (4–8.5) |
5.68 (4–6.3) |
7.4 (6–12) |
6.45 (4.5–8.5) |
Leaf length width ratio | 2 (1.7–3.12) |
1.6* (1.4–1.8) |
1.69* (1.43–1.79) |
2.02 (1.8–2.8) |
1.67 1.4–1.7 |
2 (1.79–2.2) |
Leaf mucro length | 0.4 (0.4–0.5) |
0.5 (0.4–0.6) |
0.45 (0.4–0.5) |
0.5 (0.4–0.6) |
0.34 (0.3–0.5) |
0.45 (0.4–0.5) |
Petiole length | 1.8 (1.4–2.5) |
2.61* (1.5–3) |
2.22* (1.5–3) |
3.35 (2–3.5) |
2.17 (1.8–2.5) |
2.39 (1–3) |
Petiole width | 0.2 (0.2–0.3) |
0.31 (0.3–0.5) |
0.4 (0.3–0.5) |
0.23 (0.3–0.4) |
0.3 (0.3–0.4) |
0.3 (0.3–0.4) |
Number of flowers per inflorescences | 2 | 5* (2–8) |
4* (2–6) |
5 (2–8) |
2 (2–4) |
2 (2–4) |
Bud length | 1.2 (1–1.6) |
1.47 (1.2–1.6) |
1.48 (1.4–1.6) |
1 (0.7–1.2) |
1.5 (1.4–1.6) |
1.65 (1.5–1.7) |
Bud width | 1 (0.9–1) |
0.8 (0.8–1) |
0.79 (0.7–0.9) |
0.43 (0.3–0.6) |
1 (0.8–1.1) |
0.8 (0.7–0.8) |
Bud length width ratio | 1.2 (0.9–14) |
1.81 1.69–2.23 |
1.87 (1.74–2.28) |
2.39 (1.81–2.51) |
1.68 (1.2–1.81) |
2.06 (1.79–2.32) |
Peduncle length | 1 (0.8–1) |
3.15* (1.5–6) |
2.72* (2–3.5) |
3.9 (2.5–5.5) |
1.3 (1.2–1.5) |
1.85 (1–2.5) |
Peduncle width | 0.5 (0.4–0.6) |
0.3 (0.3–0.5) |
0.4 (0.3–0.5) |
0.2 (0.2–0.3) |
0.5 (0.4–0.5) |
0.4 (0.3–0.4) |
Petal length | 0.8 (0.7–1) |
0.8 (0.8–1) |
1 (0.9–1.1) |
0.8 (0.7–0.9) |
1.2 (1–1.2) |
1 (0.9–1.1) |
Petal width | 0.2 (0.2–0.3 |
0.3 (0.3–0.4) |
0.4 (0.3–0.4) |
0.3 (0.2–0.4) |
0.4 (0.3–0.4) |
0.3 (0.2–0.3) |
Stamen number | 12 (9–14) |
8* | 4* | 8 | 12 (8–16) |
12 (8 – 16) |
Stamen length | 0.8 (0.8–1.1) |
0.7 (0.7–0.9) |
0.7 (0.5–0.7) |
0.5 (0.4–0.6) |
0.8 (0.4–1) |
0.6 (0.4–0.8) |
Style length | 0.1 (0.06–0.12) |
0.1 (0.08–0.12) |
0.1 (0.08–0.12) |
0.4 (0.3–0.5) |
0.12 (0.08–0.15) |
0.3 (0.28–0.41) |
The morphometric analysis shows that R. mucronata var. alokii has closest similarity with R. mucronata than to other Rhizophora taxa (Fig.
India. North Andaman: Austin Creek, mangrove forest (Fig.
Rhizophora mucronata var. alokii (A) habit (B) stem base with stilt roots (C) bark (D) branches (E) leafy branch end with flowers (F)leaf apex with mucro (G) inflorescence (H) minute bract at dichotomous inflorescence branch (I) mature bud with minute bracteole below calyx (J) cross section of bud (K) mature propagules (L) thick leathery petal (M) stamens (N) flower (O) pistil showing four-sided ovary (P) flower with one petal removed (Q) pear-shaped fruit (R) stamens with pollen.
Tree: columnar to spreading, height to 20 m, evergreen (Fig.
Rhizophora mucronata var. alokii is currently known only from Austin Creek, North Andaman, India.
It grows in a mangrove forest along the banks in an intermediate estuarine position in association with Rhizophora apiculata, R. mucronata and Ceriops tagal.
Flowering December to March; fruiting April to July.
Named in honour of Dr. Alok Saxena (Principal Chief Conservator of Forests) for his inspiration and his outstanding contribution to mangrove conservation in the ANI.
Rhizophora mucronata var. alokii was collected only from Austin Creek (North Andaman Islands). At this site ca. 15 individuals were observed and hence it is assumed to be rare. At present, until further areas can be sampled the species can be accessed as “Data Deficient” (DD), using the criteria of
Rhizophora species are very similar and can be difficult to distinguish (
Diagnostic characters of Rhizophora species of the ANI. The hybrids do not produce seeds so hypocotyl characters are not present in them and therefore not included in the table.
Component | Attributes | R. apiculata | R. mucronata var. mucronata | R. mucronata var. alokii | R. stylosa | R. × annamalayana | R. × lamarckii |
---|---|---|---|---|---|---|---|
Leaves | Leaf shape | narrowly elliptic | ovate, broader at base | elliptic | narrowly obovate broader at apex | broadly elliptic | narrowly elliptic |
Leaf apex | acute | acute | obtuse | obtuse | acute | acute | |
Leaf base | cuneate | broadly acute to rounded | cuneate | cuneate | cuneate | attenuate to cuneate | |
Inflorescences | Position relative to leaves | matures below | matures within | matures within | matures within | matures within | mature within |
Flower number | 2 | 2–8 | 2–6 | 2–8 | 2–4 | 2–4 | |
Juncture number | 1 | 1 to 3 | 1 to 3 | 1 to 3 | 1 to 2 | 1 to 2 | |
Bract condition | corky | smooth, minute | smooth, minute | smooth, conspicuous | smooth, swollen | smooth swollen | |
Mature flower bud(closed) | Bud length | 1–1.6 cm | 1.2–1.6 cm | 1.4–1.6 cm | 0.7–1.2 cm | 1.4–1.6 cm | 1.5–1.7 cm |
Bud width | 0.9–1 cm | 0.8–1 cm | 0.7–0.9 cm | 0.3–0.6 cm | 0.8–1.1 cm | 0.7–0.8 cm | |
Shape x-section | rounded | rounded | slightly four- sided | rounded | four-sided | rounded | |
Bud length /width ratio | 1.2 | 1.81 | 1.87 | 2.39 | 1.68 | 2.06 | |
Petal x-section | flat | enclose stamens | thick folded | enclose stamens | curved | curved | |
Petal margin | glabrous | Hairy | velvety hairy | hairy | slightly hairy | slightly hairy | |
Style length | 0.08–0.12 cm | 0.08–0.12 cm | 0.08–0.1 cm | 0.3–0.4 cm | 0.08–0.12 cm | 0.2–0.4 cm | |
Stamen number | 9 to 14 | 8 | 4 | 8 | 8–16 in two whorls | 8–16 in one whorls | |
Mature hypocotyls | Expanded fruit | cork -like | pear- like | pear- like | pear-like | ||
Hypocotyl length | 20–40 cm | 50–80 cm | 40–60 cm | 21–35 cm | |||
Distal shape | bluntly pointed | narrowly pointed | narrowly pointed | narrowly pointed |
Rhizophora hybrids are recognized by intermediate morphology and absence of advanced reproductive stages (
Distinguishing R. mucronata and R. stylosa is often problematic. Style length is the main feature used to differentiate these taxa;
All previously described Rhizophora species have eight or more stamens, whereas R. mucronata var. alokii has four stamens. Rhizophora mucronata var. alokii closely resembles R. mucronata var. mucronata in its minute bract and bracteoles, bark texture, and bud shape, but can be distinguished not only by stamen number but also by its dense foliage, laterally folded leaves, thick leathery petals with dense hairs, shorter peduncle, and four-sided ovary. It can be difficult to distinguish var. alokii from var. mucronata without the presence of flowers. Differences in flowering time is likely to make this taxon reproductively isolated. A key to the ANI species of Rhizophora is given below.
1 | Peduncle shorter than petiole | 2 |
– | Peduncle as long as or longer than petiole | 4 |
2 | Mature flower bud and fruits below the leaves; inflorescences two-flowered; bract corky, brown; hypocotyl present | R. apiculata |
– | Mature flower buds within the leaves; inflorescences 2-4-flowered; bract smooth and green; hypocotyls not present | 3 |
3 | Leaves broadly elliptical; styles 0.8–1.2 mm long; stamens in two whorls, inner shorter; mature flower bud four-sided in cross-section | R. × annamalayana |
– | Leaves narrowly elliptical; styles 2–3 mm long; stamens in one whorl; mature flower bud rounded in cross-section | R. × lamarckii |
4 | Stamens 4, petals thick and leathery, densely hairy | R. mucronata var. alokii |
– | Stamens 8; petals thin, hairy at margin | 5 |
5 | Bract and bracteoles minute; style 1 mm long, seated on elongate, tapering ovary; hypocotyls 50–80 cm long | R. mucronata var. mucronata |
– | Bract and bracteoles prominent, forming two-lobed, cup-like structure; style 3-4 mm, seated on short ovary; hypocotyls 20–40 cm long | R. stylosa |
We are extremely grateful to the Principal Chief Conservator of Forests, Andaman and Nicobar Islands for his guidance and ensuring we had the necessary support in the field. We also appreciate the cooperation and support provided by the CCF (Research and Working Plan), Territorial Circle and all the Divisional Forest Officers and their staff in the Department of Environment and Forests, Andaman and Nicobar Administration. Thanks are due to Dr. N. Krishnakumar, IFS, Director, Institute of Forest Genetics and Tree Breeding, Coimbatore, for his support and encouragement. Special thanks are extended to Mr/Mrs/Miss/Ms DFO Mayabunder for constant support.