Calligonum comosum L`Her is a large perennial bush, found in desert scrub and waste in any climatic zone. It inhabits much of the North African desert, the desert sands of the Middle East, Pakistan as well as the sand dunes in both central and eastern Arabia (Lipscombe Vincent, 1984). This species belonging to family polygonaceae and characterizes by being tall, evergreen shrub reaching up to 3 m in length, but is usually found in bush from 1 to 2 m high. The woody hard stem is white to grayish-white with swollen nodes. It looks leafless, as hard, widely branched plant, but young branches are green and thin with very small caduceus leaves (Chaudhary, 1999). The stiff, green branches produce an abundance of flowers in the early spring months (March and April). Flower pedicels are as long as or longer than the perianth. The silvery-white sweet smelling little blooms are followed by the hairy fruits which are yellowish green, yellow or even shades of red (Chaudhary, 1999). The fruits covered by long hairs which arising from four vertical wing-like narrow ridges. The plant has a long tap root which enables the plant to collect sand and used as sand dune stabilizer (Zoghet and Al-Alsheikh, 1999).
This plant has a lot of uses by Bedouins; they used the woody stem as firewood
in winter. The long and far reaching roots make it a good sand stabilizer and
the sand is often heaped around it in large hummocks (Lipscombe Vincent, 1984).
It is used in hedges, ground cover, windbreaks and landscaping. Its fresh flowers
can be eaten as it is high in sugar and nitrogenous components (Surviva-Appendix
B, 2002). The plant has been used to treat stomach ailments by local healers
and the stems and leaves are chewed for curing toothache (Liu et al.,
2001). Its root decoctin is used for gum sores (Zoghet and Al-Alsheikh, 1999).
For all of these economical uses, the plant has been faced with unorganized rural activities which led to the extinction of it in many places. For this and because of the little available information about that species especially its taxonomical plasticity under the arid conditions which it faces and as a step forward to know the ways its internal and external features adapted to the environmental stress, this work has been done.
The aim of this study is to elucidate both morphological and anatomical variations present in Calligonum comosum L`Her grown in two apart deserts in Saudi Arabia; Nefoud El-Shakika and El-Dahnaa; as both have different soil characters and climatic conditions. Also, we want to know the ways of adaptation the plants have to accommodate with the poor soil, severe climatic conditions and the water deficit in these arid habitats.
MATERIALS AND METHODS
Two sites have been chosen in Saudi Arabian deserts, one in Nefoud El-Shakika south Onyza city on Najd plateau and the second west El-Dahnaa in the way between El-Riyadh city and El-Damam, Kingdom of Saudi Arabia. Each of these locations were dominated by Calligonum comosum L`Her beside other species such as Artemisia monosperma, Ephedra elata and Haloxylon ammodendron.
Plants were collected from the two regions in February and March 2003. Parts of the stem have been taken from at least 10 plants from each location; Nefoud El-Shakika and El-Dahnaa; for investigations. Flowers and fruits have been collected in March and April of the same year. These specimens have been subjected to the following investigations:
||Parts of the stems have been examined by both Stereo and Scanning
microscopes to examine the external surface.
||Recent parts of the stems have been sectioned transversely, manually,
to examine the difference in internal structures.
||Longitudinal sections in the stems have been examined by the scanning
electron microscope, in order to examine the wood vessels.
||Anthers, pollen grains and fruits have been examined by both stereo- light
and scanning microscopes.
||Small pieces of the stems have been subjected to x-ray analyses, in order
to known the variations in element contents within the two locations.
All the measurements are in centimeter except those for pollen grains are in
micron. At least 10 plants are measured, the measured nodes and internodes are
those number five from the terminal bud. Measurements of the fruits include
the hairs covering it till the tip of the hairs. Statistical analysis using
SPSS programs of the measurements showed insignificant variations between the
studied specimens of each location, while variations in vegetative characters
can be considered between the two locations.
From Table 1 and Fig. 1, we can notice that the size of the plant, both length and width, differ between both habitats. In Nefoud El-Shakika, the plant is taller in general, but it has different width (Fig. 2), while in El-Dahnaa the maximum length of the plant is greatly shorter than that in the previous region during the same time while the mean of the width are slightly bigger (Fig. 3). The stem color grayish or grayish white with inter-node length reach 6.6 cm in Nefoud El-Shakika and never exceed 4.5 cm in El-Dahnaa. The nodes are generally swollen and reach 1.3 cm in the first region and become slightly larger in the second region.
The flowering time differs in the two sites, as it starts in the mid of February
in Nefoud El-Shakika and delayed about two weeks in El-Dahnaa. This is followed
by the fruiting time which is after the flowering time by two weeks.
||Morphological characters studied in Calligonum comosum
LHer (measurements in cm)
|| Variations in mineral contents
The fruits are rectangular in shape with four longitudinal rows of hairs. The
length of the fruits is about one cm in both regions, but their colors differ
in both regions. In Nefoud El-Shakika, the fruit color is mostly yellow with
few ones yellowish-pink (Fig. 4), while in El-Dahnaa region
the fruits are mostly red with few ones yellowish-pink (Fig. 5).
The hairs covering the fruits are about 2 mm. in length with straight ends.
The surface view of the fruit cells appear to be elongated with straight walls
and longitudinal cutin striations on upper walls of Nefoud El-Shakika fruits
(Fig. 6) and undifferentiated in El-Dahnaa ones which are
completely covered by needle-shaped wax secretions (Fig. 7).
The anthers are connected to the filaments in versatile position (Fig.
8); the epidermal cells are diametric with striated epicuticular secretions
(Fig. 9). The pollen grains are symmetric, iso-polar and perprolate
in shape, they have three colpi which are extent towards near the poles (Fig.
10). Pollen length and width as well as the colpi length do not differ greatly
between the two regions (Table 1).
||Calligomum comosom LHer in Nefoud El - Shakika
||Calligomum comosom LHer in El-Dahnaa
||Fruits of Nefoud El-Shakika
||Fruits of El-Dahnaa
||SEM of the fruit cells of Nefoud El-Shakika
||SEM of the fruit cells of Nefoud El-Dahnaa
||SEM of the whole another, showing versatile attachment with
||SEM of part of the another showing the another cells
||SEM of the pollen grain
||SEM of the stem surface of Nefoud El-Shakika showing the needle-shaped
||SEM of the stem surface of El-Dahnaa showing platelets wax
||SEM of the stem of Nefoud El-Shakika showing the papillate
|| SEM of El-Dahnaa showing the papillate epidermal cell
|| SEM of the xylem vessels showing the reticulate lignified
|| Anatomical characters studied in Calligonum comosum LHer
The texture of the stem is either mealy in the first region, or scaly in the second one. The examination of the transverse sections in the uppermost parts of the stem by light microscope reveals that the epidermal cells covered with a layer of cutin which obviously differs in thickness in the two regions. The epidermal cells are barrel - shaped with a layer of sub epidermal cells composed of compact rectangular parenchyma cells without intercellular spaces.
|| Mineral contents in Calligonum comosum LHer
The cortex is composed of three to six layers of chlorenchyma cells. The primary
vascular bundles are from five to eight with wide vessels and compressed phloem.
The stem quickly starts the secondary growth, which becomes obvious in the vessels
and phloem which sooner become circular layers of both secondary phloem and
xylem. In this state air-chambers appeared between the cortex and the secondary
phloem in the stems of El-Dahnaa region only.
|| Variations in mineral contents
The size of the secondary phloem differs as well between the two regions which
is larger and more organized in Nefoud El-Shakika than in El-Dahnaa. The type
of secondary xylem differs also, as it appears to be porous, with parenchyma
cells in between the vessels in Nefoud El-Shakika in contrast to the non porous
xylem in El-Dahnaa. The ray cells are rectangular in shape, continuous in El-Dahnaa
and discontinuous in Nefoud El-Shakika (Table 2).
The examination of the stem under the scanning electron microscope reveals that there is a wax layer over the stem surface, which is sparse and needle-shaped in Nefoud El-Shakika (Fig. 11) while it is condensed and platelets- shape in El-Dahnaa (Fig. 12). In both regions, there are areas in the epidermis with elevated papillae (Fig. 13 and 14). In longitudinal sections the xylem vessels appears with reticulate lignified walls (Fig. 15).
The Mineral contents in the tissues of the plant differ between the two regions in their examination by x-ray. From Table 3 and Fig. 16, we can notice that Sulfur and Potassium contents are noticeably higher in those grown in Nefoud El-Shakika, while Phosphorous, Cupper and Zinc are bit higher in the same area than those grown in El-Dahnaa. In contrast to Magnesium, Chlorine and Calcium contents which are greatly higher in El-Dahnaa and Silicon is a bit higher as well (Fig. 16).
The study of the effect of habitats on the phenotypic characters of wild plants
has been a matter of interest since long time ago. This subject has been called
phenotypic plasticity which is the way of response to the change in environments.
Shaltout et al. (1989) found that morphological characters, especially
leaf apices and margins, in Thymelaea hirsute (L.) Endl. Grown along
different environmental gradients in Western Mediterranean region of Egypt have
been changed according to both aridity and CaCO3 contents in the
soil. Taia and El-Olayan (2003) found that moisture content, leaf characters
as well as the length of the plants and their vital status can be affected under
||Climatic sketch for El-Dahnaa desert during the period from
||Climatic sketch for Nefoud El-Shakika desert during the period
Meanwhile Taia and El-Ghanem (2004) found that mineral contents of the plants
can be affected as well. In Calligonum comosum the leaves are deciduous
as soon as the plant start growing, thus, we cannot notice any change in the
leaves. According to our results the most vegetative characters affected by
different habitats are plant length, width and colors. The colors of flowers
and fruits can be affected also. But the main parts of the flower as well as
anther shape, ornamentation, attachment with filament beside characters of pollen
grains are stable. This indicates that floral characters are more stable than
vegetative ones. Tomlinson (1984) pointed to the use of vegetative morphological
characters in the systematic of higher plants are of limited use than morphological
features of the sexual reproductive system due to the belief in the innate conservatism
of reproductive features. White (1979) said that the plant body is made up of
an indefinite number of repeating units, which he called them modules. These
modules have a greater diversity of possible functions and for that the vegetative
characters have a great capacity for replication repair in contrast to flowers
which have set of functions which are invariable.
Taia and El-Ghanem (2004) found that leaf characters can be used in systematic,
while stem characters are more variable. This may be due the modular system
proposed by White (1979). Barthlott (1984) gave precise micro structural features
of seed surfaces which provide valuable taxonomic information. In this study
the fruit micro structural characters are more valuable than fruit color and
size. The presence of the multi-cellular appendages in four longitudinal rows
is a good character, which is invariable according to different habitat. Cellular
arrangement of inter appendages areas are stable as well; the only variable
thing is the wax deposition which may be due to climatic and other ecological
factors. The density of wax, which is less in Nefoud El-Shakika, can be referred
to the climate which is more humid than in El-Dahnaa (Fig. 17
The internal structures of desert plants give an idea about their adaptation with the external stress falling on them. Lyshede (1977) studied the structure of the epidermal and sub-epidermal cells of both Anabasis articulate and Calligonum comosum and found that the epidermal cell walls of the stem, in the two studied species, swelled rapidly during water absorption and released the water slowly when dehydrated. Slatyer (1967) reported that criteria in pine wood and he nominated it as hysteresis. According to our observations, the stem in both regions, covered with wax depositions, beside the cutinized epidermal cells which can protect the cells from water loss. The only places which permit water exchange are the stomata and the lenticels. Meanwhile, Jonsson (1902) noticed the presence of large amount of Mucilage in the epidermal outer wall in Calligonum sp. This may be another reason for preventing losing water as mucilage able to absorb and store water. All these anatomical characters; wax deposition, cutinized epidermal cells and mucilage beside the morphological characters indicate to the highly adaptation of this species to the aridity present in the habitats where it present.
The vegetative value of range plants has been studied by many authors. Oelberg (1956) studied the different factors affecting the nutritive value of range forage. Heneidy (1987) studied the nutrient content in range plants grown at Omayed region in Alexandria, While Sharaf El-Din et al. (1998) studied the nutritive value of the raudhas plants in central Saudi Arabia. They all found that, the nutritive value of any forage is dependent upon its content of energy - producing nutrients and nutrients essential to body growth. Sharaf El-Din et al. (1998) found that the evaluated species have low contents of N, P, K and Na but high contents of Ca, Mg and Mn. Taia and El-Ghanem (2004) the habitats can affect the contents of some minerals in the same species as Fe, Mn, K and Zn during the three seasons (autumn, winter and spring). In our results, the mineral content is generally low, except the potassium which is moderate in the studied regions. In spite of that, we can notice that Mg, P, S, Cl and Ca contents varied between the two regions. This means that the mineral content is affected by the habitats and accordingly the nutritive value of the plant can be affected. Abdel-Salam (1985) found that the ratio of Ca:P is the most important thing in the animal diet, as he said that it is preferred to be from 2 to three. In Calligonum comosum this ratio is more than three in El-Dahnaa region (6.59/2.06), while it is less than two in Nefoud El-Shakika (3.55/2.78) which means that nutritive value of range plants can be affected in the different habitats.
From this study, we can say that Calligonum comosum L`Her is completely adapted with the arid habitats, both morphologically and anatomically. The morphological characters can be altered according to environmental changes, but the floral characters are more fixed but those concerning the colors are affected with the mineral composition of the soils. Anatomical characters, especially those related to protection, altered according to the stress the plant face especially climatic stress. Mineral contents are affected by the habitats, as well; accordingly the nutritive value of the plant can be changed in the different habitats and under different climatic factors.