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Flora 201 (2006) 108119
Morpho-anatomical differentiation of the balkan populations of the speciesTeucrium flavum L. (Lamiaceae)$
Branislava Lakusic a,, Dmitar Lakusic b, Radisa Janc ic a, Branka Stevanovic b
aFaculty of Pharmacy, Institute of Botany, University of Belgrade, Vojvode Stepe 450, 1100 Belgrade, Serbia and MontenegrobFaculty of Biology, Institute of Botany and Botanical Garden )Jevremovac*, University of Belgrade, Takovska 43,
11000 Belgrade, Serbia and Montenegro
Received 3 January 2005; accepted 26 May 2005
Abstract
Ecological plasticity, i.e., inter-population differentiation of the species Teucrium flavum was analyzed on the basis
of morpho-anatomical variability of its five populations from the maquis (Cisto-Ericetea and Cisto-Micromerietea),
rocky grounds (Festuco-Brometea) and rocky crevices (Asplenietea rupestris) in the Eumediterranean and sub-
Mediterranean region. Univariate statistic analysis included 22 quantitative characters related to the leaf and stem
anatomy and morphology. In order to establish the variability and significance of morpho-anatomical differentiation,
principal component analyses (PCA), multivariate analyses of variances (MANOVA), discriminant components
analysis (DCA) and clustering, according to the UPMGA method based on Mahalanobius distances, have been done.
The morpho-anatomical analysis of plants from the five distant populations confirmed that the species T. flavum
belongs to malacophyllous xeromorphic species. It was established that the plants from all the five populations
analyzed are distinguished by stable conservative xeromorphic characteristics. There is a difference between the
pronounced xeromorphic plants belonging to Eumediterranean populations and the subxeromorphic sub-
Mediterranean ones.
r 2005 Elsevier GmbH. All rights reserved.
Keywords: Teucrium flavum; Evergreen shrub; Morphology; Anatomy; Leaf; Indumentum
Introduction
The Mediterranean species Teucrium flavum L. belongsto Sect. Chamaedrys (Miller) Schreber (Tutin and Wood,
1972), which includes about 30 taxa, at the species and
subspecies rank, distributed mostly in the Mediterranean
Basin. The species range extends over the entireMediterranean Basin, from the eastern coasts of Spain
across France, Italy, Croatia, Serbia and Montenegro,
Albania and Greece, to Turkey in the east, and in the
north of Africa in Algeria, Tunisia and Morocco (Meusel
et al., 1978) (Fig. 1).
T. flavum is an evergreen, branchy, semi-woody shrub,
often over 50 cm tall, that belongs to the life form of
suffruticose chamaephytes. By such a habit T. flavum
markedly differs from other representatives of the sect.
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www.elsevier.de/flora
0367-2530/$- see front matter r 2005 Elsevier GmbH. All rights reserved.
doi:10.1016/j.flora.2005.05.001
$This paper represents a part of the Ph.D. thesis of B. Lakusic ,
entitled Morphological Variability and Ecological Differentiation of
Species of Genus Teucrium L. (Lamiaceae) in Yugoslavia defended at
the Faculty of Biology, University of Belgrade, in the year 2000.Corresponding author.
E-mail addresses: [email protected] (B. Lakusic ),
[email protected] (D. Lakusic ), [email protected]
(B. Stevanovic ).
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Chamaedrys which might indicate the relict character of
the species and its belonging to the ancient Mediterra-
nean flora (Tutin and Wood, 1972). On the basis of
investigation of flowers and inflorescenses of the genus
Teucrium, Ka stner (1978) introduced a new classifica-
tion of the genus, in which the species T. flavum is
included in Sect. Pollium Schreber.
In the Balkan Peninsula T. flavum is a strictly
calciphilous plant that inhabits limestone and dolomite,
at altitudes between 0 and 200 m. It is an important
element of maquis and garrigue vegetation as well as of
their degradation forms in the Mediterranean and sub-
Mediterranean floristic region (Lakusic , 2000).
The aim of the present study was to establish whether
there exists a morpho-anatomical differentiation be-
tween Eumediterranean and sub-Mediterranean popula-
tions of the xeromorphic species T. flavum, bearing in
mind the environmental, particularly climatic differ-
ences between their habitats. Three out of five popula-
tions analyzed here developed under conditions of the
Eumediterranean climate, on the coasts of the Adriatic
and Aegean Sea. Another two populations inhabit sub-
Mediterranean locations (the Montenegro hinterland, in
the canyons of Cijevna and Moraca rivers), character-
ized by the perhumid-sub-Mediterranean Adriatic cli-
mate (Table 1).
Material and methods
Plant material and morpho-anatomical analysis
A morpho-anatomical analysis was done on plant
samples from five populations of the species T. flavum
growing in the Adriatic (Montenegro) and Aegean
(Greece) part of the Mediterranean Basin. The collected
plant material was either placed in a herbarium or fixed
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Fig. 1. Map of distribution of Teucrium flavum L.
Table 1. Ecological characteristics of the habitats of the analyzed populations
Budva(Montenegro)
Lustica(Montenegro)
Peloponnesus(Greece)
Canyon of Cijevna(Montenegro)
Canyon of Moraca(Montenegro)
Biogeography Adriatic province
of Eumediterranean
region
Adriatic province
of Eumediterranean
region
Aegean province of
Eumediterranean
region
Adriatic province
of
Submediterranean
region
Adriatic province
of
Submediterranean
region
Vegetation Rocky crevices
(Asplenietea
rupestris)
Maquis (Cisto-
Ericetea)
Maquis (Cisto-
Micromerietea)
Rocky grounds
(Festuco-Brometea)
Rocky grounds
(Festuco-Brometea)
Substratum Limestone Limestone Limestone Limestone Limestone
Altitude 40 m 80 m 80 m 200 m
Average annual
temperature
1516 1C 1516 1C 1718.5 1C 1016 1C 1016 1C
Average Januarytemperature
78 1C 78 1C 8.510.5 1C 15 1C 15 1C
Annual
precipitation
13002300 mm 13002300 mm 350600 mm 15003100 mm 15003100 mm
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in 50% alcohol and deposited, respectively in the
Herbarium of the Institute of Botany and Botanical
Garden Jevremovac, Faculty of Biology, University
of Belgrade (BEOU) and Herbarium of the Institute of
Botany, Faculty of Pharmacy, University of Belgrade
(HFF).
Voucher specimens:
1. Budva (Montenegro Eumediterranean): rocky
vegetation (class. Asplenietea rupestris), at the alti-
tude of 40m (Lakusic, D., 25 May 1995, HFF
Fix.no. Bu 01-02).
2. Lustica Stari Krasic i (Montenegro Eumediterra-
nean): maquis (class. Cisto-Ericetea), limestone, at
the altitude of 80 m (Lakusic, D. & B. 2225/96, 27
July 1996, BEOU, HFF Fix.no. TFS).
3. Peloponnesus (Greece, Peloponnesus Eumeditera-
nean: maquis (Stevanovic, V., May 1995, BEOU
Fix.no. TF).
4. Canyon Cijevna, village Dinosa (Montenegro sub-Mediterranean): rocky vegetation (class. Festuco-
Brometea), limestone (Lakusic, B., Jancic, R., Slav-
kovska, V., 09 July 1997, HFF Fix.no. 11).
5. Canyon of Moraca, Dromir (Montenegro sub-
Mediterranean): rocks above the river Moraca (class.
Festuco-Brometea) (Lakusic, B., Slavkovska, V.,
Jancic, R. 12 July 1997, HFF Fix.no. 67).
Anatomical analyses of leaves and stems were done
on permanent slides, prepared by the standard method
for light microscopy. Cross-sections of the leaves (150
samples) and stems (50 samples) were cut on a Reichertsliding microtome (up to 10 mm thick). The sections were
cleared in Parazone and thoroughly washed before
staining in safranin (1% w/v in 50% ethanol) and alcian
blue (1% w/v, aqueous).
Epidermal peels (150 samples), for surface structures
and stomata analyses, were prepared using Jeffreys
solution (10% nitric acid and 10% chromic acid, 1: 1)
and stained in safranin and alcian blue. All slides were
mounted in Canada balsam after dehydration.
Density and type of the leaf and stem hairs, as well as
the paradermal aspect of epidermal cells, were also
studied with SEM (JOEL JSM-6460), for which the
samples were covered by gold.
All morpho-anatomical measurements were done
with the Image Analyzer System Ozaria 2001 and the
data processed in the statistical package Statistica 4.5
for Windows. For each of the quantitative characters, 30
leaf samples and 10 stem samples were obtained from
different individuals belonging to each of the five
populations analyzed.
Twenty-two quantitative characters of the statistical
analysis were grouped in three categories: I, Leaf
anatomy characters (13); II, Leaf shape characters (4)
and III, Stem anatomy characters (5).
I. Leaf anatomy characters: (1) Height of adaxial
epidermal cells; (2) thickness of palisade tissue; (3)
thickness of spongy tissue; (4) height of abaxial
epidermal cells; (5) number of palisade layers; (6)
surface area of adaxial epidermal cells; (7) surface
area of abaxial epidermal cells; (8) surface area of
abaxial stomata; (9) number of abaxial stomata;(10) number of adaxial glandular hairs; (11)
number of abaxial glandular hairs; (12) number of
adaxial non-glandular hairs; (13) number of abaxial
non-glandular hair.
II. Leaf shape characters: (14) Leaf length; (15)
distance between the largest leaf width point and
the leaf top; (16) the largest width of the leaf; (17)
leaf surface area.
III. Stem anatomy characters: (18) Stem diameter; (19)
stem diagonal; (20) stem cortex thickness; (21)
thickness of the stem vascular cylinder; (22) stem
pith diameter.
Statistical analysis
For each of the quantitative characters a univariate
statistic analysis was done on the basis of the following
parameters: average value, minimum, maximum, stan-
dard deviation and standard error. The significance of
differences between the populations studied was estab-
lished by multivariate analyses of variances (MANO-
VA). The general structure of the sample variability
were established by Principal Component Analysis
(PCA). For checking the hypothesis that the analyzed
sample was composed of discrete groups, which are
morphologically differentiated one from the other, a
Discriminant Component Analysis (DCA) was done.
Overall differences between the compared groups are
presented by Mahalanobius distances, which are used
for clustering on the basis of UPGMA method.
Results
Leaf shape and anatomy
The leaves of T. flavum are elliptically oval, being the
widest at the basal part, and rounded at the tip. The leaf
margin is obtusely dentate. The leaf stalk is long. It
should be pointed out that the leaf shape was always the
same in all the populations studied.
In general, in all the populations studied the leaf
length was between 12 and 27 mm, whereas the leaf
width ranged between 11 and 21 mm. The leaf surface
area varied between 80 and 370 mm2.
The leaf indumentum of all the plants studied
was composed of glandular and non-glandular hairs
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(Fig. 2A). The glandular hairs were peltate and capitate.
Peltate hairs (Fig. 2B, D) consisted of a short unicellular
stalk and a multicellular secretory head with large
subcuticular space. Capitate hairs were small in size and
of three types on the basis of their structure: Type I
consisted of a short unicellular stalk and a rather large
secretory head of four cells with a small subcuticular
space (Fig. 2B, D); Type II consisted of a short
unicellular stalk and a secretory head of one or two
cells; Type III consisted of a two-cellular stalk and a
secretory head of one cell (Fig. 2C). The non-glandular
hairs are unicellular, basally widened, sharp on the top
(Fig. 3B) or multicellular, mostly having two to three
cells, uniseriate, branchless, the top cell having a sharp
edge, straight or bended (Fig. 3C). More or less wart-
like cuticular structures are observed on the surface of
the non-glandular hairs (Fig. 3D).
The glandular hairs are at the bottom of the complex
arrangement of the leaf indumentum, leaning against the
epidermal cells, while between them there are dispersed,
long non-glandular hairs that form its upper layer. Basal
cells of the glandular hairs are sunk under the level of
epidermal cells, and their large heads (composed of
several secretory cells) are in contact, leveling with theepidermis or being a bit above thus partially covering
the leaf blade (Fig. 3A).
The indumentum is particularly well developed on the
abaxial leaf side (Fig. 3A), which is a common feature of
plants from all five populations. Therefore, the abaxial
leaf side is grayish-green in color. The plants from the
Eumediterranean populations, namely from the local-
ities near Budva and Krasic i, as well as from Pelopon-
nesus in particular, are characterized by conspicuously
thick indumentum (Fig. 4). In contrast, the adaxial leaf
side is always covered with sparse hairs rendering a dark
green color to this side (Fig. 3E and Fig. 4).
The cuticle on the leaf adaxial epidermis is thicker
than that of the abaxial epidermis in plants of all the five
populations studied. Besides, the outer epidermal cell
walls are thickened, particularly in the adaxial epidermis
occupying 2/3 of the cell lumen. The plants of the sub-
Mediterranean populations (from the gorges of Cijevna
and Moraca) are characterized by larger adaxial
epidermal cells in respect to those of the plants of
Eumediterranean populations (Fig. 5).
Anticlinal walls of the adaxial and abaxial epidermal
cells are almost straight in the plants from the localities
near Budva and Krasic i (Fig. 6B), or slightly undulate,
as in the plants from Peloponnesus and from theMoraca and Cijevna canyons (Fig. 6A). On the outer
periclinal walls of the abaxial epidermal cells larger or
smaller cuticle wrinkles are formed.
The leaves are always hypostomatic; the stomata are
more or less raised (Fig. 7C) above the epidermal cells, of
diacytic and anomocytic type (Fig. 7A). Their frequency
varies from 129 to 300per mm2. The highest number of
stomata are present in the plants from Krasic i
(186300 permm2), and the lowest in those from the
Moraca canyon (129186 per mm2) (Fig. 8). The stomata
are usually encircled by the glandular hairs (either peltate
or capitate), thus being partially covered with the
subcuticular spaces of the secretory cells (Fig. 7BD).
Leaf thickness (Fig. 9) of all plants studied ranged
between 210 and 440 mm, being the thickest in the plants
from the canyon of Cijevna (267440 mm).
The mesophyll is clearly differentiated into palisade
parenchyma and spongy parenchyma; the ratio of these
two photosynthetically functional mesophyll tissues is
generally 1.4:1, except in the plants from the locality
near Budva, being 2:1 (Fig. 9).
The palisade parenchyma, just below the upper
epidermis, consists of 23 rows of elongated and densely
arranged cells, which gradually shorten going towards
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Fig. 2. Teucrium flavum A, indumentum of glandular (g) and
non-glandular (h) hairs on the lower leaf side. (SEM) B, peltate
(p) and capitate type I (k) hairs. C, capitate hair type III
(SEM). D, Paradermal view, peltate (p) and capitate type I (k)
hairs.
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the spongy parenchyma. The anticlinal walls of the
palisade cells are almost always undulate. The cells of
spongy parenchyma are usually irregularly shaped, but
with relatively small intercellular spaces (Fig. 10A, B).
Even in the leaves of the plants from Peloponnesus,
which are smaller and less thick, the palisade parench-
yma is the thinnest but still densely packed into 23
layers, which is always the case in the plants of all the
populations studied.
In the leaf cross-section, a large number of vascular
bundles, situated in the central region of the mesophyll,
and only one main vascular bundle, developed in the
leaf midrib, are observed. Large bundle sheath cells
enclose the vascular bundles.
Stem shape and anatomy
T. flavum is an evergreen, branchy, semi-ligneous
shrub. In general, the resemblance of the external
morphology of the stem of all different populations is
obvious. In all the populations studied, the stem height
was between 40 and 70 cm, and a basal ligneous part is
clearly developed and reaches the length of up to 30 cm.
However, slight differences could be observed between
the population groups growing in very different
ecological conditions. In the individuals from Eumedi-terranean populations the height of the shrubs usually
varies in between 40 and 45 cm. The internodia are very
short and dense, so that the leaves overlap each other.
Contrary to them, the shrubs of the sub-Mediterranean
populations reach a height of over 60 cm, having longer
internodia; therefore their leaves mostly do not overlap.
The herbaceous stem of T. flavum specimens is more
or less square-shaped (in the cross section), firm,
particularly in the plants from the localities near
Budva and Peloponnesus, as well as from the Cijevna
canyon (Fig. 11A). Seldom, as in the plants from the
localities from the Moraca canyon it is slightly rounded
(Fig. 11B). The stem is well covered with epidermis, and
the thick cuticle, permeated by wax deposits and
glandular (peltate and capitate) and non-glandular
hairs, is arranged in a similar way as in the leaves.
Scattered stomata are slightly raised above the level of
the surrounding epidermal cells.
The stem cortex is differentiated into two to three
layered subepidermal supporting tissues, collenchyma,
and several layers of thin-walled parenchymatous cells
with prominent intercellular spaces. The collenchyma is
discontinuously distributed in the peripheral part of the
stem, forming thick projecting strands particularly in the
stem corners.The vascular tissue commonly forms a cylinder
between the stem cortex and the pith, consisting of
collateral vascular bundles separated by interfascicular
parenchyma. Conspicuous cups of sclerenchymatous
fibres are present above the phloem, being particularly
large below the stem corners. These fibres are more
developed in the vascular cylinder of plants from the
localities of Moraca and Cijevna canyons as well
as in those from Peloponnesus. However, in the stem
of plants from the other two populations there are o
nly 23 sclerenchyma cells above the phloem elements.
The correlation coefficient of the cortex and the whole
stem diameter ranges from 0.226 (Krasic i) to 0.343
(Cijevna).
Multivariate analysis of the morpho-anatomical
characters
By PCA it could be shown that the structural
variability of the populations studied is extremely
complex, since the first three axes comprise only
47.58% of total variability. By MANOVA statistically
significant differences between all populations were
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Fig. 3. Teucrium flavum A, indumentum on the lower leaf side(SEM). B, three-cellular hair. C, bicellular hair. D, wart-like
structures on the surface of the non-glandular hairs (SEM).
E, indumentum on peeled upper epidermis.
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established. It should be pointed out that the most
important characters in structural differentiation are
those related to leaf shape, stem anatomy, indumentum,
and leaf anatomy features in this order of significance
(Table 2).
DCA of the populations studied of T. flavum
has shown that the Eumediterranean (Peloponnesus,
Krasic i, Budva) and sub-Mediterranean (Moraca,
Cijevna) populations represent two morphologically
almost completely separate groups. On the first two
axes, the populations from Peloponnesus and Budva
stand completely separated from the sub-Mediterranean
populations. The population from Krasic i shows
(Fig. 12) transitional characteristics between the
Peloponnesus and Montenegro sub-Mediterranean
populations, as it was the case also in the PCA analysis.
Morpho-anatomical separation between Mediterranean
and sub-Mediterranean populations is clearly observed
also on the basis of overall Mahalanobious distances
(Fig. 13).
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Fig. 4. Box and whisker plots of basic statistic parameters of indumentum.
Fig. 5. Box and whisker plots of basic statistic parameters of epidermis.
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Discussion
The analyzed populations of the species T. flavum
inhabit the Mediterranean area on terra-rossa (red
soil) substrate, which develops on porous limestone. The
species grows within the maquis-garrigue vegetation of
different stages of progression and regression, undervarious Mediterranean bio-climate conditions perhu-
mid Mediterranean Adriatic, arid Mediterranean Ae-
gean and perhumid sub-Mediterranean Adriatic climate.
The resemblance of plants from different populations is
obvious, even at first sight, due to the similar general
habit, i.e., of quite a similar external morphology of the
stem and evergreen leaves. It is rather important to
stress this uniformity of the species T. flavum that
contrastes to the extreme morphological heterogeneity
that is present within the whole genus Teucrium. A
detailed growthform analysis of Teucrium have shown
significant morphological differences between shrubs,
semi-shrubs and perennial and annual herbs, especially
in regard to the extension and volume of lignification, as
well as with respect to the existence or the lack of
sclerenchyma elements in the cortex. Some of these
features can be used taxonomically on the level of
sections and species groups (Ka stner, 1978, 1979,
1981, 1986).
The macromorphological similarity of the stems and
evergreen leaves of T. flavum populations might be
assumed as a strong indication of structural stability and
some kind of morpho-anatomical conservatism of this
ancient Mediterranean xerophyte. However, this phy-
siognomic uniformity obviously is combined with eco-anatomical differentiations of leaves and stems of T.
flavum populations which thrive both in sites with
summers not particularly dry, and in those with a
pronounced summer drought.
In general, the evergreen leaves of T. flavum are
xeromorphic, moderately to significantly thick, tough
but not flabby neither rigid nor hard. In the Mediterra-
nean vegetation there is a large number of xerophytes
with such leaves, commonly known as malakophyllous,
notably within the genera of Cistus, Rosmarinus,
Thymus, etc. (Breckle, 2002; Kummerow, 1973).
The prominent xeromorphic features of the T. flavum
leaves are: simple form and relatively small size, dense
indumentum, especially on the lower side where a high
number of stomata are also located. The smallest leaves,
having a reduced external surface and mesophyll
thickness, are found in plants from the Eumediterra-
nean, Peloponnesian locality. In contrast, the thickest
leaves with the largest lamina surface area have the
plants from the sub-Mediterranean locality in the
canyon of Cijevna.
A dense and complex indumentum, composed of
glandular and non-glandular hairs, covers the lower
leaf side, shielding stomata and thus advantageously
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Fig. 6. Teucrium flavum paradermal view A, undulate anticli-
nal walls of the upper epidermal cells of plants from Moraca.
B, straight anticlinal walls of the upper epidermal cells of
plants from Budva.
Fig. 7. Teucrium flavum A, anomocytic (a) and diacytic (d)
stomata. B, stomata encircling by the glandular hairs or
glandular hairs encircling stomata. (SEM). C, highly raised
stomata and cuticular striae. (SEM). D, peltate hair around
the stomata (SEM).
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reducing transpiration loss. Stomata and glandular
hairs are very closely related, meaning that the stomata
are surrounded by glandular hairs or glandular hairs
are surrounded by stomata. In any case, stomata are
partially or totally flanged by the large subcuticular
swellings of peltate hairs and/or secretory cells of the
capitate hairs. Since the protrusions of capitate secretory
cells have only a small storing space, there is a
continuous evaporation of essential oils (Werker et al.,
1985a, b). This renders the air near the leaf surface more
condensed thus providing a higher boundary layer
resistance to gas diffusion. Regardless of the small
quantity of essential oils (0.10.2%), which characterizes
the specimens of T. flavum, even their minimal presence
in the external secretory structures may be efficient in
reducing both transpiration and overheating (C orovic et
al., 1969; Todorovic and Stevanovic , 1994). Otherwise,
it is well known that all species of the genus Teucrium
are distinguished by only a low quantity of essential oils
(Kovacevic et al., 2001; Petric ic et al., 1993).
Beside essential oils, some other terpenoids, as well
as flavonoids and/or phenylcarbonic acids might be
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Fig. 9. Box and whisker plots of basic statistic parameters of mesophyll.
Fig. 8. Box and whisker plots of basic statistic parameters of stomata.
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produced by these glandular hairs (Wollenweber, 1984).
Terpene exudates are the resins that cover the surface of
the plant above-ground parts, while the flavonoids are
incorporated either into the resins or into the coating the
leaf surfaces of many plants from the semi-arid regions
(Kelsey et al., 1984; Wollenweber, 1984). It has been
reported previously that the resin content in T. flavum
leaves is about 1.03%, consisting of terpenes, another
phenolic compounds, and free flavonoids (Kovacevic et
al., 1998). All these mostly aromatic volatile compounds
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Fig. 10. Cross section of the leaf: A, from Krasic i. B, from Peloponnesus.
Fig. 11. Cross section of the stem: A, square-shaped stem. B, rounded stem.
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on the upper leaf side consisting of short and protruding
non-glandular hairs and of all the types of glandular
hairs mentioned, especially in plants from the Eumedi-
terranean populations, also have an important influence
on the spectral features of the leaves. Such structural
adaptations increase leaf reflectance, thus reducing solar
inception, heat load and therefore water deficit. This hasbeen reported for leaves of Mediterranean species from
the genus Cistus (Gausman and Quisenberry, 1990).
It is worth mentioning that the more dense indumen-
tum of leaves from the Peloponnesian population must
be regarded as a favorable adaptive modification which
helps in protecting the mesophyll from excessive water
loss and intense radiation in this particular hostile,
perarid Mediterranean environment.
More or less conspicuous xeromorphic characteristics
ofT. flavum, from different populations, are represented
by a relatively high number of stomata, ranging from
129 to 257 per mm2 in the plants from the sub-
Mediterranean sites to 143300 per mm2 in those from
the Adriatic coast and the Peloponnesus. A similar high
number of stomata was established also in the Apennine
populations of T. flavum, in which the number of
stomata varies from 168 to 258 per mm2 (Ka stner, 1979).
It is also a typical xeromorphism that the dense,
complex indumentum on the lower leaf side protects
stomata which, on the other side are somewhat raised
above the level of the epidermal cells.
Smaller and thick-walled epidermal cells on the upper
leaf side are a pronounced xeromorphic feature of the
Eumediterranean populations of the taxon, compared
with the two sub-Mediterranean ones. The anticlinalwalls of both adaxial and abaxial epidermal cells of
plant leaves from all populations studied are straight to
wavy, which is described as an other xeromorphic
feature (Fahn and Cutler, 1992).
A ratio between 1.4:1 and 2:1 of 24 layered palisade
parenchyma to 23 layered spongy parenchyma is
characteristic for plants from all the five populations.
The number of palisade layers is increased in the plants
from Eumediterranean populations, particularly in
those from the localities near Budva and Krasic i, but
also in those from Peloponnesus. Moreover, the palisade
cells of these plants are narrower and more compact. In
addition, in leaves of these groups of plants of spongy
cells can be found, which elongate in such a way that
they resemble palisade cells. A partial differentiation
into an isolateral mesophyll is asumed to be a strongly
xeromorphic character. Again, similar characteristics of
the palisade and spongy tissues were established also in
the Apennine populations of T. flavum (Ka stner, 1979).
The stems of the studied T. flavum populations are
also protected by a thick cuticle with waxy layers and
with a dense indumentum of the same structural pattern
as that of the leaves. The stem hairs are more protruding
and less intertwined than those on the leaves. The ratio
of the stem cortex to stem diameter ranges from 0.226 to
0.343, which is within the usual values found in
xeromorphic stems (Fahn and Cutler, 1992).
All the data obtained, particularly those subjected to
a comparative multivariant analysis of morpho-anato-
mical characteristics of the five populations from three
different climate variants, have shown that the speciesT. flavum has maintained quite a stable, conservative
morpho-anatomical structure. Such a substantial simi-
larity between different populations is also characteristic
of other ancient Mediterranean plants since their
adaptive structures evolved, in the first place, as the
consequence of severe summer drought and high
temperatures (Margaris, 1981). In all the localities, both
eu- and sub-Mediterranean ones (arid-Mediterranean
and perhumid-sub-Mediteranean), the plant popula-
tions of which have been studied, more or less
pronounced, longer or shorter intervals of summer
drought stress prevail. Inter-population differences refer
to small variations in leaf size, indumentum density,
number of stomata, thickness of cuticle and outer
epidermal cell walls, as well as to the number of the
mesophyll tissues layers. While all these anatomical
features are of the same pattern, they are clearly more
expressed in the Eumediterranean than in the sub-
Mediterranean populations.
Acknowledgements
The authors are grateful to Prof. Dr. Vladimir
Stevanovic , Institute of Botany and Botanical garden
Jevremovac University of Belgrade for useful advice
and valuable comments and to the Ministry for Science,
Technology and Development of Serbia (Project Nos.
1568 and 1505) for financial support.
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