Philippine Journal of Science
145 (3): 259-269, September 2016
ISSN 0031 - 7683
Date Received: ?? Feb 20??
Xerophytic Characteristics of Tectona
philippinensis Benth. & Hook. f.
Jonathan O. Hernandez1, Pastor L. Malabrigo Jr.1, Marilyn O. Quimado1*,
Lerma SJ. Maldia1, and Edwino S. Fernando1
Department of Forest Biological Sciences, College of Forestry and Natural
Resources, University of the Philippines Los Baños, College, Laguna
1
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.
Key words: anatomy, arid or semi-arid, endemic, Lamiaceae, restoration, xerophytes.
INTRODUCTION
The 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
*Corresponding author: [email protected]
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Philippine Journal of Science
Vol. 145 No. 3, September 2016
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 study
The 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 specimens
Three 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
260
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 analysis
The 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
Stem
The 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
Philippine Journal of Science
Vol. 145 No. 3, September 2016
Hernandez et al.: Morpho-anatomy of Tectona
philippinensis Leaf and Stem
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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Hernandez et al.: Morpho-anatomy of Tectona
philippinensis Leaf and Stem
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.
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.
Leaf
The 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 SerratoValenti 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,
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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 singlelayered of oblong to columnar parenchymatic cells. This
Hernandez et al.: Morpho-anatomy of Tectona
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Philippine Journal of Science
Vol. 145 No. 3, September 2016
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
336.5
220.9
Palisade mesophyll
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
STEM
T. philippinensis
Epidermis
182.5
C. ramiflora
27.0
26.0
Parenchyma
591.2
329.2
Sclerenchyma
294.9
158.0
Collenchyma
389.7
238.0
1504.2
702.8
Xylem
383.0
386.4
Phloem
323.6
316.4
Vascular bundles
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.
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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Hernandez et al.: Morpho-anatomy of Tectona
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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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Hernandez et al.: Morpho-anatomy of Tectona
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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.
DISCUSSION
Results 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
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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
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Hernandez et al.: Morpho-anatomy of Tectona
philippinensis Leaf and Stem
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
Philippine Journal of Science
Vol. 145 No. 3, September 2016
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
Hernandez et al.: Morpho-anatomy of Tectona
philippinensis Leaf and Stem
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.
ACKNOWLEDGMENTS
The 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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