xerophytic characteristics of tectona philippinensis benth

Philippine Journal of Science145 (3): 259-269, September 2016ISSN 0031 - 7683Date Received: ?? Feb 20??

Key words: anatomy, arid or semi-arid, endemic, Lamiaceae, restoration, xerophytes.

Xerophytic Characteristics of Tectona philippinensis Benth. & Hook. f.

1Department of Forest Biological Sciences, College of Forestry and Natural Resources, University of the Philippines Los Baños, College, Laguna

*Corresponding author: [email protected]

Jonathan O. Hernandez1, Pastor L. Malabrigo Jr.1, Marilyn O. Quimado1*, Lerma SJ. Maldia1, and Edwino S. Fernando1

Tectona philippinensis Benth. & Hook.f. is one of only three species in the genus Tectona (Lamiaceae) restricted to the Asian tropics. It is endemic to Ilin Island and Batangas Province on Luzon Island, Philippines and is regarded as a critically endangered species. While role of xerophytic characteristics of plants are very important for their survival and growth under various environmental pressures, such characteristics in native tree species remain unclear. In this study, the anatomy of the species was analyzed to determine the xerophytic characteristics of T. philippinensis. Histological paraffin technique was used to examine the anatomical structures of leaf and young stem of the species. The anatomical structures of T. philippinensis have the characteristics typical of xerophytic plants. This includes the presence of four types of trichomes, extended and well-developed vascular system, and multiple layers of palisade and sclerenchyma cells. Extension of extended vascular bundles to both non-glandular hairs on the adaxial surface and glandular hairs on the abaxial surface of leaf is reported for the first time in this study. Therefore, anatomical structures of this species suggest its ability to survive under marginal conditions. However, studies on ecophysiology, pot experiments/field trials, phenology, and associated vegetation of the species are suggested to further understand its habitat preference and adaptation mechanisms.

INTRODUCTIONThe genus Tectona L.f. (Lamiaceae) includes only three species of trees restricted to the Asian tropics, viz., Tectona grandis L.f. occurring in India, Laos, Mynamar, and Thailand; Tectona hamiltoniana Wall., endemic to Myanmar; and Tectona philippinensis Benth. & Hook.f., endemic to the Philippines. T. hamiltoniana occurs in the central dry zone of Myanmar (Kiyono et al. 2007; Aye et al. 2014), while T. grandis is known from a wider range of climatic conditions, including dry areas, throughout its natural range (Kaosa-ard 1981; Gyi & Tint 1998). Both these species are known to be deciduous trees.

T. philippinensis is known only from Ilin Island and Batangas Province on Luzon Island, usually along dry hills and exposed limestone ridges along the coasts and is also deciduous (Caringal et al. 2015). It is commonly called Philippine teak, but is also known locally by the vernacular names malabayabas and bunglas. The species is regarded as critically endangered (Fernando et al. 2008, Madulid et al. 2008). The few remaining populations have been reported to be threatened by habitat destruction through land conversion and development. Significant conservation efforts of the species include the Biodiversity Management Bureau (BMB) initiated project on ex-situ conservation areas for the Philippine teak (PAWB-DENR

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1998) and non-government organizations and academe initiated certain in-situ conservation strategies (Agoo & Oyong 2008).

Many anatomical characteristics have been recognized as protective mechanisms that allow the plants to survive against various levels of environmental pressure. For example, the seven types of trichomes and their density through in vivo leaves of T. grandis were linked to extreme dependence of the species, especially those young ones, for storing water during the developmental stage. In vitro leaves, on the other hand, due to poor development of epidermal structures (e.g. trichomes) were reported to have higher water loss than those of in in vivo leaves (Bandyopadhyay et al. 2004). Stephanou & Manetas (1997) reported the features of leaves enable plants to tolerate adverse conditions in the site such as drought, high air temperature, UV-B radiation, among others. Plants that are well-adapted to such conditions commonly referred to as xerophytes exhibit certain adaptive mechanisms to complete their life cycle in dry environments (Atia et al. 2014). They have special modifications such as leaves that are trichomous, with thick cuticle (Richardson & Berlyn 2002), high palisade tissue/spongy tissue ratio, and well developed water-storing and water-transporting tissues to minimize the rate of transpiration. Many of the species in the family Lamiaceae have long been reported to have xerophytic characteristics such as in the case of Salvia sclarea L. (Ozdemir & Senel 1999), Teucrium montanum L. and Teucrium polium L. (Dinç et al. 2011). There is no report yet on xerophytic characteristics of T. philippinensis. This study analysed the anatomical structures (leaf and young stem) of T. philippinensis to determine the species’ xerophytic characteristics.

MATERIALS AND METHODS

Place and duration of the studyThe anatomical examination of leaf and stem was conducted at the Microtechnique Laboratory of the Department of Forest Biological Sciences (DFBS), College of Forestry and Natural Resources (CFNR), University of the Philippines Los Baños (UPLB) from August to October 2015.

Preparation of specimensThree sample replicates for each leaf and stem of T. philippinensis were collected from Lobo, Batangas, located at 400 masl. Samples of a non-xerophytic plant, Cynometra ramiflora L. were collected from Arbor Square, CFNR - UPLB. The leaf and/or stem sample for both species was obtained from c.a. 6-8 cm long from the

apical portion of an orthotropic branch. For leaf sample, a small piece measuring 1mm2 was transversely cut in the median to include the midrib. For stem sample, on the other hand, approximately 1-2 mm long was also transversely cut along the main axis of the stem using a sharp Gillete razor blade. The illustrations of these procedures are presented in Figure 1.

Histological paraffin technique was used (Johansen 1940) (Figure 2). Samples were fixed in 1:1 mixture of FAA-A (12ml 37% Formaldehyde, 88ml 95% Ethanol) and FAA-B (10ml Glacial Acetic Acid, 88ml, and 90ml water) for three weeks. They were dehydrated following series of solutions of water, ethyl, and tertiary butyl alcohols from 50% to 100% for four days. Gradual infiltration followed using a 1:1 mixture of paraffin oil and tertiary butyl alcohol for three days in the oven at 650C. Embedding the samples in the melted condition of paraffin wax followed. The samples were then mounted into 1.5cm x 1.5cm x 2cm wooden blocks. Mounted samples were sectioned using a rotary microtome (American Optical 820) at a thickness of 10µm. Cross sections were mounted on microscope slides coated with Haupt’s solution, air-dried for three days, and stained with 1% Safranin and were counter stained with 0. 5% Fast green.

Microscopic examination and analysisThe typologies of anatomical structures were identified following the manual on anatomy of dicot plants. The thicknesses of all visible dermal, ground, and vascular tissues were measured. Characteristics of other structures such as stomata and trichomes were also examined.

All the cross sections obtained were observed under a compound microscope (Euromex 0112987, manufacturer: BlueLine Holland) equipped with a camera which was connected to a desktop computer. The scale of all the measurements was calibrated at 40x magnifications.

The mean thicknesses of the observed anatomical structures for both species were calculated using some functions in MS Excel. Comparison of anatomical structures between T. philippinensis and C. ramiflora was made.

RESULTS

StemThe stem of T. philippinensis is six-angled (Figure 3) and its surface is occupied with glandular trichomes – capitate, peltate, and branched (Figure 5). The hypodermis is four to six-layered of collenchyma cells. The rest of the cortex is composed of 591.2µm thick, oval to round parenchyma

Hernandez et al.: Morpho-anatomy of Tectona philippinensis Leaf and Stem

Philippine Journal of ScienceVol. 145 No. 3, September 2016

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Figure 1. Young leaf and stem of an orthotropic branch as the plant material of the study showing (a) length of sample used (b) part of leaf where the samples were obtained (c) size of cross section samples put inside the microcentrifuge tubes and (d) size of stem samples put inside the microcentrifuge tubes.

Figure 2. Procedures of paraffin technique used in this study showing (a) fixation (b) dehydration (c) infiltration (d) embedding (e) microtoming (f) mounting on slide (g) staining (h) microscopic examination which were conducted at Microtechnique Laboratory of CFNR-UPLB.

cells with intercellular spaces. The vascular tissue is of collateral bundle type, measuring 1504.2µm thick, where the xylem is of endarch configuration (Figure 3). Xylem measures 383.0µm. Xylem fibres and xylem parenchyma were also present. The phloem cells are small, polygonal, measuring 323.6µm in thickness. There are 2-3 layers of phloem sclerenchyma- fibres (294.9µm thick) that cap the phloem cells. Phloem parenchyma and xylem parenchyma were also observed in the vascular bundles.

The pith enclosed by the vascular cylinder is built up of round and polygonal parenchymatous cells and 4-5 clumps of compactly arranged thick walled sclerenchyma cells (Figure 3).

The mean thickness of each of the observed anatomical structures of C. ramiflora is presented in Table 1. Stem is irregular in shape without trichomes in its surface (Figure 4). Epidermis is single-layered of round to



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oval-shaped epidermal cells. The hypodermis is one to two-layered of collenchyma cells, which measure 238.0µm in thickness. Next to it is the cortical layer which is built up of two to three layers of parenchyma cells. This layer measures 329.2µm in thickness. There are four to five vascular bundles. Each measures 702.8µm in thickness. These vascular bundles are of collateral type. Xylem and phloem measure 386.4µm and 316.4µm thick, respectively. There are one to two layers of sclerenchyma cells (158.0µm thick) which form the phloem cap. Pith is parenchymatic.

LeafThe average thickness of each observed anatomical structure in leaf of T. philippinensis is presented in Table 1. Both epidermises are uniserriate. Lower epidermis is wavy in appearance (Figure 6b). Using the works of Serrato-Valenti et al. (1997), Ascensa~o et al. (1999), Zheng (2001), Gersbach (2002), Huangz et al. (2008), four types of trichomes were identified, namely: non-glandular on the adaxial surface, glandular capitate, glandular peltate,

and glandular branched on the abaxial surface (Figure 5). Stomata are of hypostomatic type. The palisade mesophyll (336.5µm thick) is one to two-layered of elongated parenchymatic cells. The spongy mesophyll (444.4 µm) is multi-layered. The vascular bundles in the secondary veins are transcurrent. (Figure 6b). The xylem (49.5µm thick) faces toward the upper epidermis while the phloem (13.8µm thick) faces toward the lower epidermis (Figure. 6a). In the midrib, the phloem is found in both sides of the xylem (Figure 6a). Three to six layers of sclerenchyma cells that cap the phloem toward the periphery. Thick layer of parenchyma cells (1390.4 µm thick) in either side of main strand of vascular bundles was observed. Thick sclerenchyma cells that cap the phloem cells were present.

The freehand cross section of leaf of C. ramiflora and the average measurement of each observed anatomical structures are presented in Figure 7 and Table 1, respectively. Upper and lower epidermises are uniserriate. The former measures 70.7µm while the latter measures 93.4µm in thickness. The palisade mesophyll is single-layered of oblong to columnar parenchymatic cells. This

Figure 3. Stem cross section of T. philippinensis showing (a) overview of stem (b) simple and complex tissues, and (c) sclerenchyma cells in pith. Abbr.: ep – epidermis, p – parenchyma, sc – sclerenchyma, co – collenchyma, ph – phloem, xy – xylem, and vb –vascular bundle. The bar represents 100µm.



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Figure 4. Freehand stem cross section of T. philippinensis showing (a) overview of stem (b) simple and complex tissues, and sclerenchyma cells in pith. Abbr.: ep – epidermis, p – parenchyma, sc – sclerenchyma, co – collenchyma, ph – phloem, xy – xylem, and vb – vascular bundle. The bar represents 50µm.

Table 1. Average thickness in micrometers of anatomical parts of stem and leaf of Tectona philippinensis and Cynometra ramiflora. n=3 leaf/stem samples.

LEAF T. philippinensis C. ramiflora

Upper epidermis 99.1 70.7

Lower epidermis 95.6 93.4

Palisade mesophyll 336.5 220.9

Spongy mesophyll 444.4 329.2

Midrib 4932.6 1644.2

Parenchyma (midrib) 1390.4 327.6

Sclerenchyma (midrib) 488.5 244.2

Collenchyma (midrib) 839.6 279.5

Vascular bundles (midrib) 2603.9 1252.0

Vascular bundles (blade) 952.0 452.2

Xylem 358.0 279.7

Phloem 194.8 182.5

STEM T. philippinensis C. ramiflora

Epidermis 27.0 26.0

Parenchyma 591.2 329.2

Sclerenchyma 294.9 158.0

Collenchyma 389.7 238.0

Vascular bundles 1504.2 702.8

Xylem 383.0 386.4

Phloem 323.6 316.4

layer measures 220.9µm thick. The spongy mesophyll is multi-layered which measures 329.2µm thick. The vascular bundles in the secondary veins are of embedded type of pattern. The xylem (279.7µm thick) faces toward the upper epidermis while the phloem (182.5µm thick) faces toward the lower epidermis (Figure 7a). The midrib is adaxially convex and abaxially concave. This measures

1644.2µm in thickness. In the midrib, one to two layers of collenchyma cells (279.5µm) next to epidermis are observed. This is followed by only two to three layers of parenchymatous cells (327.6µm thick) towards the main strand of vascular bundles (1252.0µm thick). One to two layers of sclerenchyma cells in the form of phloem cap cells (244.2 µm thick) surround the vascular bundles.



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Figure 5. Trichomes observed in stem and leaf of T. philippinensis showing (a) non-glandular type in adaxial surface of leaf, (b) capitate glandular type in leaf and stem (c) peltate glandular type in leaf and stem, and (d) branched glandular type in leaf and stem. The bar represents 100µm.

Figure 6. Leaf cross section of T. philippinensis showing (a) midrib and (b) leaf blade. Abbr.: p – parenchyma, sc – sclerenchyma, co – collenchyma, nt – nonglandular trichome, pgt – capitate glandular trichome, bgt- branched glandular trichome, st – stoma, pm – palisade mesophyll, sm – spongy mesophyll, tv – transcurrent vascular bundle, ph – phloem, xy - xylem, enclosed by a red oval shape is the tv showing its extension to both non-glandular and glandular trichomes. The bar represents 100µm.



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DISCUSSIONResults show that the leaf and stem of T. philippinensis have the characteristics typical of xerophytic plants when compared to the anatomical structures of C. ramiflora, a non-xerophytic plant. These characteristics have long been recognized as protective mechanisms of plants to survive against adverse conditions in a particular site (Stephanou & Manetas 1997) and as adaptive mechanisms of plants to complete life cycle in dry environments (Atia et al. 2014).

First, the hypodermal layer in stem of T. philippinensis is remarkably thicker than that of C. ramiflora. This conforms to the general differentiation of anatomical structures between mesophytes and xerophytes (Roth 1984). In T. philippinensis, this layer which is reinforced by multi-layered water-storing parenchymatic tissue may help the species to store water under drought conditions especially during summer. Well-developed water-storing cells are prominent in xerophytes serving as special modifications to minimize the rate of water loss through transpiration. In this context, in times of

low water availability, T. philippinensis can obtain water or moisture from its water-storing cells specifically in the cortex. Roth (1984) also reported that water-storing tissues may be developed in xeromorphic organs such as the multi-layered collenchymatous hypodermis when the environment conditions become complicated. The role of collenchyma and sclerenchyma cells in stem has extensively been associated with mechanical support in growth and development (Leroux 2012; Qureshi et al. 2013). The presence of these thick simple tissues in stem may be explained by the need to increase the strength, mechanical, and flexibility providing tissues of the species. Further, the vascular structure of T. philippinensis seems to be directly associated with the efficient passageway of water and other dissolved solutes from the soil that needed to be transported throughout the plant body as the tree grows in limestone substrate.

Second, the characteristics of the dermal tissues of T. philippinensis remarkably differ from that of C. ramiflora. In the latter, the observed characteristics resemble the typical or common anatomical structures of most vascular

Figure 7. Freehand leaf cross section of C. ramiflora showing (a) overview of leaf and (b) vascular bundles and mesophyll tissues. Abbr.: sc – sclerenchyma, co – collenchyma, pm – palisade mesophyll, sm – spongy mesophyll, vb –vascular bundle, ph – phloem, xy - xylem, le – lower epidermis, and ue – upper epidermis. The arrow shows the embedded vascular bundle.



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plants (e.g. mesophytes) such as some species reported in the works of Ashton & Berlyn (1994), Rabelo et al. (2012), and Qureshi et al. (2013). In the former, the wavy epidermal characteristic is in conformity with what was reported typical of species in the Lamiaceae family as in the case T. grandis (Hoft 2004), T. montanum L., and T. polium L. (Dinç et al. 2011) and in the Myrtaceae species such as Eucalyptus maculata Hook (Stocker 1960). Similar to plants of most Lamiaceae species and in the species of Asteraceae and Solanaceae families (Maffei 2010), the presence of trichomes is one of the most expressed xerophytic characteristics of T. philippinensis. Seven types of trichomes are also observed through in vivo leaves of T. grandis (Bandyopadhyay et al. 2004). Presence of these trichomes may suggest possible indicator of water requirements of T. philippinensis owing to the characteristics of its habitat (specifically poor soil water holding capacity) in Lobo, Batangas. As remarked by Glover (2000), trichomes are prominent in water economy. Specifically, the non-glandular trichomes have been extensively described as hairs providing shade on the leaf surface to maintain a humid layer and reduce water loss through evaporation especially when stomata are open. Hence, presence of trichomes in T. philippinensis suggests low water loss through transpiration. The glandular trichomes, besides their role in water economy, on the other hand, have multicellular head cells which secrete secondary metabolites such as essential oils, terpenes, phenolic compounds (De & Aronne 2007), and alkaloids which have long been hypothesized to evolve as toxic to herbivores and microbes attacking the plants (Ranger & Hower 2001; Wagner et al. 2004).

Further, important characteristics found in the leaf of T. philippinensis are the hypostomatic stomata often surrounded by glandular trichomes – emerged from invaginations making the surface wavy. In most desert plants, these invagination structures, according to Field et al. (1998) are often blocked by trichomes which might further reduce transpiration.

Next, a study by Bezic (2003) reported the same structure of palisade tissue (Figure 6b) in the case of Spartium junceum L., a xerophyte and a well-adapted species to high salt concentration. This structure is also reported in Dinarvand & Zarinkamar (2006) in the case of Ziziphus nummularia (Burm.f.)Wight & Arn. Such structure of mesophyll tissues is expressed as adaptation of plants, which often considered a response of plants to high light intensity (Lemos-Filho 2000; Bosabalidis & Kofidis 2002) and defense against herbivory (Solbirg & Orians 1977). The presence of additional layer of elongated palisade parenchyma is also recognized as a way to increase the water use efficiency (i.e. ratio of CO2 fixed to water lost) (Lewis 1972). Furthermore, this structure of palisade

mesophyll in T. philippinensis supports the anatomy of sun-loving plants which have long been characterized to have longer palisade mesophyll tissues than shade plants (Ashton and Berlyn 1994; James and Bell 2000). In C. ramiflora, on the other hand, the structure of mesophyll indicates adaptation of the species to habitats which are neither too dry nor too wet. Such structure suggests habitat of species that is likely to have favourable environmental conditions (e.g. productive soil, high productivity, and high diversity of both flora and fauna). Such structure may not suggest the need to increase the photosynthetic efficiency, storage, and mechanical support of the species with respect to the prevailing environment condition (e.g. xeric environment).

The vascular bundles in secondary veins of leaf are of vertically transcurrent structure. When veins are transcurrent, the parenchyma cells on either side in the vascular bundles extend all the way between the bundle and the upper and lower epidermis (Metcalfe & Chalk 1979). Such structure has also been particularly recorded in certain Trifolieae. In some species of Caprifoliaceae, this structure of vascular bundles was also reported but the tissue surrounding the bundles and extending to both the adaxial and abaxial epidermis is sclerenchyma instead of parenchyma tissues (Jakolvljevic et al. 2014). One of the criteria of xeromorphy reported by Roth (1984) is the presence of transcurrent vascular bundle, which primarily functions as supporting tissue for the entire mesophyll. This pattern of vascular bundle is not observed in C .ramiflora which has embedded pattern of vascular bundle instead. Embedded or not transcurrent vascular bundles have long been described as characteristic of non-xerophytic plant (e.g. hydrophytes and mesophytes) (Roth 1984).

Moreover, remarkable is its extension to the base of both non-glandular and glandular hair(s) (Figure 5b). After an extensive literature review, allegedly, its reporting in this study serves as a pioneer one. This suggests a specialized support function for the entire mesophyll and enhanced storage of water and food reserves. On the upper side of the leaf, non-glandular hairs may take the role of providing shade for the parenchyma cells surrounding the tvb, whose primary function is to store water and starch. On the lower side of the leaf, besides reducing transpiration rate, glandular hairs of T. philippinenis may play the role of protecting the starch-rich storage cells from possible attack of herbivores. Such structure also suggests efficiency in the distribution of water and reserves which need to be transported throughout the plant body especially during drought conditions.

Lastly, the midrib of T. philippinenis also shows possible attributes of xerophytic plant by its thick layers of collenchyma, parenchyma, and sclrenchyma



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cells (Figure 6a). These characteristics also clearly distinguish T. philippinensis from C. ramiflora. The latter has significantly thinner layers of simple tissues (e.g. parenchyma cells) than that of the former. What has been observed in T. philippinensis is found similar to the works of Duarte & Silva (2013) and Dinarvand & Zarinkamar (2006). Xerophytes (e.g. some bryophytes) have long been characterized by having a broader lamina and a different structure of midrib Grebe (1912). Taken from the claim of Sack et al. (2015) on the role of much of the anatomical parts of a leaf on water conductance, these thick layers of parenchyma cells in midrib, consequently, may be explained by the need to increase the amount cells capable of storing water and food reserves.

In summary, xerophytic characteristics of T. philippinensis showed structural adaptive mechanisms that are mainly related to water saving and mechanical support for the species. The population of T. philippinensis is reported to thrive along coastal forests, littoral cliffs and exposed limestone substrate in Lobo, Batangas, Philippines (Caringal et al. 2015). Generally, limestone substrate is characterized by having shallow or very thin soil which consists mainly of calcium carbonate. Soils from coastal to forest zone of Lobo Watershed where small population of T. philippinensis naturally grows are generally sandy (ERDB 2003). Such soil characteristics indicate low water and nutrient holding capacity and high permeability. A bulk density value of less than 1.4g/m3 is also reported as soil characteristics of habitat of the species in Lobo, Batangas (ERDB 2003). Such value of bulk density suggests that the soil is slightly compacted. Further, the soil pH in the area is reported to be slightly acidic to acidic. This means that both macronutrients and micronutrients seem to be difficult and unavailable for plants use. All these, together with the other edaphic attributes of limestone substrates as cited in Whitford (1911), make the habitat of the species a very dry one.

Despite the condition of the habitat, population of T. philippinensis is still able to outgo such conditions. More recently, the present population of the species has been reported to compose of approximately 3,000 individuals across 14 barangays in Lobo, Batangas (Caringal et al. 2015). They further noted that despite the various pressures and threats being faced by the species in the wild, remarkably, it has a good number of regenerants. These can be attributed to its xerophytic characteristics found in leaf and stem. These characteristics have long been recognized as protective mechanisms of plants to survive against adverse conditions in a particular site (Stephanou & Manetas 1997) and as adaptive mechanisms of plants to complete life cycle in dry environments (Atia et al. 2014).

Consequently, results may imply that T. philippinensis has

a potential to be used for forest restoration of degraded areas in its natural habitat such as those in Batangas and in Mindoro. It has also potential for forest rehabilitation because its anatomical structures suggest the ability to cope with various adverse conditions in the site. In northern China, for example, many of over 1,000 native species of trees and shrubs (e.g. Pinus tabuliformis Carriere, Sabina chinensis L.) in the arid and semi-arid areas have extensively used for afforestation of heavily degraded arid habitats (Bozzano et al. 2014). A number of efforts in restoring arid land and biodiversity in China reported that native shrub communities have showed important ecological functions in conservation of soil, water, and biodiversity. It was also reported that native species (e.g. shrubs) are well adapted to dry soil, poor nutrient availability, and temperature extremes (Bozzano et al. 2014). Further, there is this restoration effort on saline soils in Eastern Cuba using native species, fast growing exotic species and fruit trees, which reported that among the mixture of species, all native xerophytic species in the area were able to survive even under severe heat and water stress (Bozzano et al. 2014).

As a conclusion, the anatomical structures of T. philippinensis conform to the general xerophytic characteristics of the species in the Lamiaceae family thriving in arid or semi-arid conditions. Therefore, T. philippinensis has the characteristics typical of xerophytic plants. Anatomical structures of this species suggest the ability to survive under marginal conditions. Hence, studies on ecophysiology, pot experiments and/or field trials, phenology, and associated vegetation of the species are suggested to enable deeper understanding about its habitat preference and adaptation mechanisms.

ACKNOWLEDGMENTSThe authors would like to thank the Metallophytes Research Laboratory of the College of Forestry and Natural Resources, University of the Philippines Los Baños for providing us the materials and equipment in the conduct of anatomical examination and analysis. This study also owes special thanks to the Philippine Tropical Forest Conservation Foundation Inc. (PTFCF) for providing financial assistance for the conduct of the study.

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xerophytic characteristics of tectona philippinensis benth

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