Intraspecific variation in some species of Euphorbiaceae from Tirunelveli hills of southern western ghats, Tamil Nadu
G.J. JOTHI* & V.S. MANICKAM
Centre for Biodiversity and Biotechnology (CBB), St. Xavier’s College (Autonomous), Palayamkottai 627 002
Abstract: A study was carried out in some species of the family Euphorbiaceae namely Actephila excelsa (Dalz.) Muell.–Arg., Blachia calycina Benth. B. reflexa Benth., B. umbellate (Willd.) Baill. and Phyllanthus macraei Muell. – Arg. in Tirunelveli hills of southern western ghats to highlight the importance of intraspecific variation in taxonomic research, by means of phenotypic plasticity. In this present study the effect of season and altitude on morphological characters are assessed.
Resumen: Se realizó un estudio de algunas especies de la familia Euphorbiaceae, a saber Actephila excelsa (Dalz.) Muell.–Arg., Blachia calycina Benth., B. reflexa Benth., B. umbellata (Willd.) Baill. y Phyllanthus macraei Muell–Arg. en las colinas Tirunelveli de la porción sur de los Gates Occidentales, con el fin de resaltar la importancia de la variación infraspecífica en la investigación taxonómica, por medio de la plasticidad fenotípica. En este estudio se evalúa el efecto de la estación del año y la altitud sobre caracteres morfológicos.
Resumo: Um estudo foi levado a efeito em algumas espécies da família das Euphorbiaceae, nomeadamente a Actephila excelsa (Dalz) Muell.–Arg., Blachia calycina Benth., B. reflexa Benth., B. umbellata (Willd.) Baill. and Phyllanthus macraei Muell–Arg. nas colinas de Tirunelveli, a sudoeste dos gahts, para clarificar a importância da variação interespecífica na investigação taxonómica pelo recurso da plasticidade fenotípica. Neste estudo foi avaliado o efeito da estação e da altitude nos caracteres morfológicos.
Key words: Actephila excelsa, altitudinal variation, Blachia calycina, B. reflexa, B. umbellata, phenotypic plasticity, Phyllanthus macraei, Tirunelveli hills.
Introduction
The intraspecific variation has not been given sufficient attention in the taxonomic research. New approaches to the presentation of ecological information and a reappraisal of intraspecific categories need to be made before ecology can become a major direct tool in plant taxonomy (Heywood 1973). The familiar formula, Genotype + Environment → Phenotype, implies that the phenotype is not merely a manifestation of the genotype, but also of environmental factors which play a part in modifying phenotype and genotype. Turesson (1922) referred to different phenotypes which were merely the product of different environments as ecophenes. The ability of a genotype to express different phenotypes according to external conditions is referred to as phenotypic plasticity or plastic responses.
Plasticity is extremely common in Bryophytes. In Pterido-phytes of southern western ghats, intraspecific variation have been described in great number of taxa (Irudayaraj et al. 1995a,b, 1996; Manickam et al. 1997). Plastic responses are also by no means confined to exomorphology. Chemical and anatomical characters are also frequently affected. Numerous cases of plasticity in leaf epidermal characters have been documented by Stace (1976) and Stace & Auquier (1978). Cook (1968) has shown that the ecophenetic response is complex and varied and that similar responses may have quite different causes and mechanisms. Assessment of phenotypic plasticity is important for taxonomists to recognize different ecophenes. Certain environments are well known to give rise to extreme ecophenes in a wide range of species, for example, adaptation to shady/sunny, wet/dry and low/high altitude situations. Certain genera or
species are also notorious for producing a wide range of ecophenes. In the present study ecophenes of a four species of Euphorbiaceae namely, Actephila excelsa (Dalz.) Muell.–Arg., Blachia calycina Benth., Blachia reflexa Benth. and Blachia umbellata (Willd.) Baill. and Phyllanthus macraei Muell.–Arg. have been observed.
Materials and methods
Study area
The present study area, Tirunelveli hills (Fig.1) is situated in the southernmost end of the western ghats. It lies between 770 10′–770 40′ E and 80 25′–80 53′ N. The elevation varies from 50 to 1868 m. Its geographical position is so unique that it has a profound effect on the vegetation and flora of the district, which has been rightly considered as “an epitome of the whole of the Madras state” (Mudaliar & Sundararaj 1954). The forest tracts of Tirunelveli hills including Thirukurungudi, Kalakad, Manholai, Papan-asam, Mundanthurai, Valayar, Ainthalaipothigai, Nagapothigai, Agasthiyamalai, Sivasilam, Court-
allam, Puliarai and Sivagiri hills have undulating topography with inhospitable terrain and undoubtedly the floristic diversity of this region is of ancient lineage (Nair 1991; Nair & Daniel 1986; Subramayam & Nayar 1974).
Vegetation
Scrub/Thorn forests: The scrub type of vegetation occurs from the foot hills and extends up to 200 m and observed in and around Sivagiri, Courtallam, Papanasam, Kalakad and Thirukur–ungudi.
Dry deciduous forests: These forests occur between 150–400 m altituide in Sivagiri, Puliarai, Courtallam (Thekkumalai) Papanasam, Kalakad, Thirukurungudi.
Moist deciduous forests: These forests are lying above the zone of dry deciduous forests and below the semi–evergreen forests in Kalakad, Thirukurungudi, Papanasam, Courtallam, (Thekkumalai) Puliarai and Sivagiri hills.
Semi–evergreen forests: This also corresponds to Tirunelveli semi–evergreen forest of Champion & Seth (1968) and occurs between 600–800 m, also rarely at higher altitudes with wet evergreen forest above and moist deciduous forest below. These forests are distributed in patches and belts wherever the moisture is available. It has been noted in Kalakad, Kannikatty and Inchikuzhi (Papanasam), Courtallam, Puliarai and Sivagiri hills.
Fig. 1. Tirunelveli Hills, Tamil Nadu, India.
Wet evergreen forests: This corresponds to southern hill top tropical evergreen forest and west coast tropical evergreen forests of Champion & Seth (1968). These forests occur roughly between 600–1500 m and are located around Courtallam, Kalakad, Papanasam and Puliarai hills.
Shola forests: According to Champion & Seth (1968) these are the southern montane wet evergreen forests and are confined to moist and sheltered valleys of Papanasam top (Poongulam, Agasthiyamalai).
Low altitude grasslands: These occur in the scrub forests and dry and moist deciduous forests and are extended upto 500 m.
High altitude grasslands: This is otherwise called as grassy swards or savannahs. They are seen as small patches on exposed rocky areas of moist deciduous to shola forests.
During the exploration of Tirunelveli hills from 1996–2001, the authors noticed the intraspecific variations in A. excelsa, B. calycina, B. reflexa, B. umbellata and P. macraei at same and different altitudes. All the specimens were
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Table 1. The recognition of ecophenetic variations of plants.
Ecophenes Description Habitat conditions Ep1
Actephila excelsa
Fig. 2. Shrubs to 2 m high. Leaves obovate or elliptic–oblong, 11.5–17×4 cm, chartaceous;
Partial shade, in deciduous to semi - evergreen forest.
deposited in Xavier’s College Herbarium (XCH), Palayamkottai, Tamil Nadu.
Results and discussion
Ecophenes are entities of a quite different nature from genetically determined variants, but they can be conspicuous in nature and they are of ecological importance. On many occasions it can be advantageous to refer to them concisely i.e. by means of a name and the system developed by Buch (1922–1928) appears to be very suitable for this purpose. In Buch’s system each ecophene is
referred to as a ‘modification’. Based on this, we have made slight modification in Buch system and named as Ecophene 1 (Ep1), Ep2, Ep3, Ep4, Ep5, respectively, as shown Table 1.
petioles to 1cm long. a, a1, b, & b1. Fruiting pedicels ca 3.5 cm long; calyx lanceolate, 2.5 - 5 × 0.1–0.8 mm, glabrous or pubescent. Fruits capsular, globose, ca 1 × 1 cm. c. Leaves elliptic–obovate, ca 8.8 x 3.3cm; petiole ca 5 mm long. Leaves obovate, ca 5 × 3.5 cm, deciduous; petiole ca 5 mm long. Fig. 3 a, b, c, d & e. Shrubs to 1m high. Leaves variously shaped and sized. Male flowers more or less same. Female flowers in a, 4–lobed, lobes broadly oblong–ovate, ca 1 × 0.6 cm; style to 1 cm long. In c, sepals lanceolate, smaller than a, petals 0. Fig. 4 a, b, c, d, e & f. Shrubs to 1m high. Leaves variously shaped and sized. Male and female flowers more or less more. Fig. 5. Male flowers are more or less same. a, b, c & d. Shrubs to 1m high. Leaves rhomboid acuminate or obovate, viz., 6.5 × 2.3, 9 x 3, 8.2 × 4 & 10.5 x 4.4 cm. Female flower : in a, pedicel to 1.5 cm long. Sepals 5–lobed, lobes lanceolate, ca 5 × 1.25 mm. In c, shrubs to 1m high. Leaves oblanceolate to rhomboid acuminate, ca 14 × 5.3 cm. In e, pedicel length and sepals length and width are lesser than b1. Fig. 6. Male flowers are more or less same. a. Stunted woody herbs to 15 cm high. Leaves elliptic to 1 x 0.5 cm. Female flowers: in a1 pedicel to 3.5 mm long; sepals 6–lobed, lobes oblong– ovate, 1.5 × 0.7 mm. b. Woody herbs to 30 cm high. Leaves elliptic– lanceolate, ca 2.2 × 1 cm. b1. Sepals lobes in female flower lanceolate, ca 8 x 0.4 mm. c. Woody herbs to 45 cm high. Leaves elliptic, ca 3 × 1.3 cm. c1. Sepal lobes in female flower ovate, ca 5 x 3.5 mm.
Full shade in evergreen forest. Partial shade, high wind blown in montane forest. Partial/Full shade, high moist/low moist condition (within deciduous forests). Partial/Full shade high moist/low moist condition (within deciduous forests). Partial/Full shade, dry condition (within deciduous forests). Partial shade, moist condition in moist deciduous forests. Partial shade, moist condition in moist deciduous forests. Dry conditions in low altitude grass land. Moist condition in moist deciduous forests. High moist conditions in high altitude grassland.
In the present study five species under three genera of Euphorbiaceae have been chosen for variability studies. A. excelsa grows from dry deciduous forest (150 m) to evergreen forest (1500 m) mostly on forest edges and so, for with standing the winds the height of the plants gets decreased. The leaves are chartaceous when the plants occur from foot hills to 1000 m, on the open shola forest it is thick coriaceous. From
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700–1000 m altitude the fruiting calyx are hairy, but it is glabrous in foot hills and in the shola forest (Fig. 2). In the floral characters, the tepals are ovate at high altitude and the petals are elliptic–ovate from 200 m to 600 m. Species of Blachia are found in dry deciduous to evergreen forests, mostly in the rocky areas. In B. calycina (Fig. 3), and B. umbellata the leaves are varied, in floral characters both male and female flowers are more or less same, the pedicel length was varied. In Fig. 4, the leaves are varied, at the same time in the female flowers, the number of tepals and their shape also varied, often tepals were pubescent. (Fig. 5). P. macraei is seen in the grassland vegetation, and the variations are mostly seen in leaves as shown in Fig. 6.
Fig. 2. Actephila excelsa (Dalz.) Muell. Arg.– collected from dry deciduous forests to evergreen forests (foot hills to 1700 m) in different localities of Papanasam Reserve Forest.
Present observations show that all the variations are due to phenotypic plasticity. There are many taxa based upon ecophenes and so each taxonomist should observe the ecophenetic characters before giving a new name to the plant. It has been pointed out by several workers (Clausen et al. 1940, 1945, 1948) that plasticity and ecotypification are alternative adaptive strategies which are both important in evolution. This is certainly so where little biosystemic research has been undertaken, particularly in the tropics and in lower plants (Stace 1980).
Fig. 3. Blachia calycina Benth.–collected in deciduousforests (150–600 m) of different Reserve Forests viz.,Papanasam, Thirukurungudi, Sivagiri and Puliarai.
Fig. 4. Blachia reflexa Benth.–collected in different sites of deciduous forests (100–500 m) from Thirukurungudi and Sivagiri Reserve Forests.
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Acknowledgements
The authors sincerely thank University Grants Commission, New Delhi, for financial assistance, Chief Wildlife Warden and other forest officials for allowing us to do field work. Thanks are also due to Dr. N.P. Balakrishnan, Scientist Emeritus, Botnical Survey of India (BSI), Coimbatore, for his valuable help in identification and to Mr. H. Sankar, artist, for illustrations.
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