Study of the bryological flora at the archaeological site of Chellah, Morocco

The Chellah archaeological site in Rabat, listed as a cultural asset since 2012 on UNESCO's World Heritage List, is subject to significant biodeterioration. The aim of this study is to identify the bryophytes that have an important impact on the destruction of the substrate. For this purpose, three prospectionswere carried out in autumn 2014, spring 2015 and winter 2016. The systematic sampling carried out allowed us to identify 20 species of bryophytes belonging to 10 botanical families, of which 4are dominant with 13 species equivalent to 65% of the total. The four families are Pottiaceae, Brachyceciaceae, Funariaceae and Bryaceae; they belong to the class of Muscinae. The liverworts are represented by only 6 species, representing 30% of the total population. Among the 20 species inventoried, 3 are newly observed in the region of Rabat: Entosthodon pulchellus (H. Philib.) Brugués; Dydimodon Fallax Hedw. and Trichostomum crispulum Bruch. When bryophytes settle on substrates, a preliminary soilis initiated to the detriment of the quality of materials and their durability.


I. INTRODUCTION
Like other historical sites in Rabat such as the Hassan tower or the Kasbah of the Udayas, the Chellah archaeological site, a melting pot of several civilizations (Phoenician, Carthaginian, Roman and finally Islamic)is one of the highlights of the capital's history. The site of Chellah, alsoknown as Chellah necropolisdue to its transformation into a royal necropolis by the Marinids sultans, has undergone several archaeological excavations since 1917 thatallowed uncovering the different occupations of the site ( (Taleb et al., 2005). However, no investigation has yet been carried out on bryophytes, but it is agreed that these plants are pioneer plants that initiate plant succession by participating in pedogenesis; their installation on old masonry participates in their biodeterioration. The aim of this study is thus to draw up a list of bryophytes species that are in the necropolis of Chellah and to see up to what extent they take part in the biodeterioration of the substrates.

II.
MATERIAL AND METHOD The archaeological site of Chellah is located within Rabat at 4 km from the Atlantic coast; itoverhangs the astrologer and astronomer Ptolemy under the name of Sala, and a river port serving as a Mediterranean counter. The site was then deserted and given up before being again occupied by the Marinids sultans who built there a necropolis named Al-Ribat Al Mubarak. An inscription in kufic script on the front gate indicates that the work was completed in 739 after hijri(AD 1339). The Marinids wall, which encircles the site, currently contains characteristic vestiges of the Roman city, including in particular the capitol, the forum, the thermal baths, a nymphaeum and a triumphal arch. From the Marinids occupation, there remain a mosque, a madrasah (Islamic school), a mausoleum, halls for ablutions and several funerary rooms (Fig. 1). The site, state-owned property, is protected since november 19, 1920 by the royal decree that defines as national historical monument all the complex of Chellah. Since 2012, Chellah is part of the sites of Rabat inscribed in the list of World Heritage of UNESCO as cultural asset. METHODOLOGY We carried out prospections in the Chellah archaeological site during three seasons: autumn 2014, spring 2015 and winter 2016. These prospections allowed us to follow the biological cycle of the encountered bryophytes, in particular their sporulation. Further investigations were concentrated on the spring season, which is the most favorable period for observing the species with the sporophyte that is necessary for identification. The sampling is systematic and the harvest is therefore carried out at each encountered bryophyte population taking care not to pick up the entire population in order to preserve the species. We sorted and identified the collected samples in the laboratory. The bryophytes are reviviscent plants that preserve very well after dehydration. Therefore, they are moisturized progressively for the identification. Species recognition was done using the following identification keys: Augier (1966 (Braun-Blanquet, 1954, Jelenc, 1955a, 1955b, 1967, Braun-Blanquet, 1954, cited by Ros et al., 1999). Elsewhere, it was reported on gravel and coastal sand by Augier (1966), and on sandy soil, or on old walls according to Boulay (1884 Augier (1966) who also observed it on calcareous stones. Smith (2004) noticed it on rocks, wet stones, top of trees, walls, streams, rivers, canals, lakes, and shady shores. At Chellah, it was harvested on limestone rocks. Rhynchostegiella curviseta (Brid.) Limpr. is a Pleurocarpus moss with a creeping stem, irregularly ramified by more or less drawn up branches from 5 to 10 mm length and unequally spaced. The drawn up leaves,lanceolate, narrow, and gradually narrowed leaves in the upper half are weakly toothed and have a vein that reaches the middle of the leafblade. The middle limb cells are more than 10 fold longer than broad. The silk is red, rough and slightly curved in S. The actinomorphic capsule is more or less inclined.  (Ros et al., 2000) observed it on the edges and cracks of granitic and quartzitic rocks and on peats between 2100 and 3300 m. It was collected on the shady limestone rocks of the studied site. Plychostomum capillare (Hedw.) Holyoak & N. Pedersen, is a 4 cmAcrocarpus moss with a circular to slightly polygonal stem. The twig has a helical shape. Leaves are spatulate, twisted in the dry state, drawn up and spread apart in the wet state. They are cogged at the apex with an excurrent vein, margined on most of their length and mainly on the upper part of the limb where two rows of longer elongated cells are observed, the other cells are less elongated (2-3 of 1 at least), of hexagonallosangic shape, having tips at the ends of their major axis. The middle of the limb has a large and loose areolation with cells of 2 to 3 on 1 in general. The sporophyte is well developed with an orange smooth silk of 2.5 cm and a rust-colored capsule of 4 mm, hanging with a double peristome.  (Jelenc, 1967, Jelenc, 1955b, cited by Ros et al., 1999); on the edges of the granitic rocks, between 2210 and 2400 m (Ros et al., 2000). It was first described in the Anti Atlas by Cano et al.in 2002. Elsewhere, it was reported on stony soils or on the wall mortar by Augier (1966) and Smith (2004) who considered it as a calcareous species. On the site of Chellah, it was harvested on limestone rocks. Bryum radiculosum Brid is a yellowish-green acrocarpus moss, dioecious in compact tufts 4-10 mm high, with well-differentiated stem, oval-lanceolate leaves of about 2 mm, acuminate, denticulate at apex, the brown-russet-red veinis excurrent, the limb is smooth with a narrow and tightly bounded area around the middle (cells measure 6/1 at least). This plant was harvested in a vegetative state during the three prospections. ,is a small acrocarpus moss of 1 cm of length, with a short, drawn up and simple stemfixed on the substrate by fine and dense rhizoids. The leaves are spread out, inserted over two rows on both sides of the stem. They are oblong to lanceolate, acute, with a dorsal blade (sheath) shorter than the limb measuring about 1/3 of the length of this one and margined byvery narrow cells that are lengthened and hyaline. The cells of the limb are isodiametric and short, square almost round. The vein is simple, excurrente in a small mucron. (5 mm). The silk is short (5 mm), red, the capsule is ellipsoidal, drawn up and green with a simple peristome made up by red teeth divided up to the middle.  Jelenc, 1955a, 1967, Braun-Blanquet, 1954, quoted by Ros et al., 1999); In the cracks and crevices of limestone rocks on wet sites with maritime influence. It was collected between the cracks of the limestone rocks of the studied site. Funariella curviseta (Schwägr.) Sérgio, is a small acrocarpic moss of 5 mm of height, forming grass between the cracks of limestone rocks, with toothed leaves in the upper part, acuminate and without clear margin. The isolation is smooth in the upper part of the limb, is more or less translucent with rectangular cells and a vein finishing close to the top. The silk is about 2 mm long. The mature capsule is brown, symmetrical, pyriform, sloping at pendulum before dehiscence and darwn up at maturity with reticulated spores of 20 μm in diameter. The capis well developed, swollen and has a long beak. The peristome is absent. It forms a stand in association with Targionia hypophylla in the studied site. *Entosthodon pulchellus (H. Philib.) Brugués (Funaria pulchella H. Philib.) It has been reported on the cracks of granitic rocks at 2100 m a.s.l. (Ros et al., 2000). It was observed on basic soils in meadow and between rocks, and referred to as calcicole by Smith, (2004). It was picked up on rocks and limestone groundsof the studiedsite. Entosthodon pulchellus (H. Philib.) Brugués is an 8 to 12 mm acrocarpus moss, forming loose turf on moist soil, the apical leaves, being larger than the others, formoval and whole rosettes. The limb is more or less translucent and terminated in a long filiform point; theareolation is smooth in the upper part, comprises rectangular cells more or less elongated from 2 to 3 in 1 at least. The vein does not reach the top of the limb. The silk is rectilinear; the capsule is oblique, and the urn is smooth. The spores are finely papillose and are about 20 µm in diameter. It was seen on the edges of granitic rocks, on quartzic soils near streams (Ros et al., 2000); as well as on the bases and trunks of Quercus rotundifolia (Draper et al., 2006). It was described as a messicole by Augier (1966), which described it as a pioneer plant on clay soil and limestone sand. It was seen on very diversified substrates by Boulay, (1884), who observed it particularly on disturbed soils or on landfills. It was collected on limestone rocks and on clay-sandy soil of the studied site.   Jelenc, 1955a, 1955b, 1967, Braun-Blanquet, 1954, cited by Ros et al., 1999). Cano et al. (2002) described it for the first time in the Anti Atlas on bare soils. Its presence was also noted on the banks of the BouRegregriver; on granite; onlimestone rocks; as well as on limestone slopes (Ahayoun et al., 2007). Boulay, (1884) and Smith (2004) cite very diverse substrates such as walls, roof tiles and cracks in rocks. Smith, (2004) argues that Tortula muralis tends to prefer basic substrates and is found more rarely on acidic substrates and is more common in urban areas where it is able to resist atmospheric pollution. At Chellah, it was harvested on limestone rocks. Tortula muralis Hedw is an acrocarpus moss about 2cm. The leaves are more or less drawn up-isolated in the wet state, contracted and twisted in the dry state, with a strong vein all along the leaf, showing in cross-section a single band of stereids, dorsal, excurrent in one hair smooth or slightly dentil, often flexuous hyaline, long; formed hyaline point, partly at least, by the vein itself. The limb is very papillose at the top, and revolute up to near the summit. The cells of the upper part of the leaf are furnished with manypapillae, they are square-subaronded, very chlorophyllian, elongated towards the middle. The basal cells are hyaline, rectangular and longer. The drawn up cylindrical capsule takes on a blackish color at maturity with a long beak opercula (¼length of the capsule), and a cupped headdress. The peristome has completely divided teeth up to the basilar membrane; it then appears formed of 32 bristles, twisted in whorl with 1-3 turns. The spores are spherical with a smooth wall about 10 µm in diameter. It develops on the ground and in the cracks at the base of moist granitic rocks (Ros et al., 2000). It has been described as a pioneer on limestone rocks, on gravelly soil and on coastal dunes by Augier (1966). Boulay, (1884), notes its presence on the sandy or marly soil of the hills, in the hollows of the rocks, on the old walls and on the fixed sands of the old dunes. According to Smith 2004, it is found in shaded or exposed basic habitats, on the ground, rocks, rocky banks, cliffs, old wall mortar, and sandy dunes. It was collected on limestone rocks of the studied site. Trichostomum crispulum Bruch. is an acrocarpusmoss, harvested in a vegetative state, light green to yellowish on surface, brown inside. The leafed stem is 1 to 1.5 cm long with mucronate acute leaves at the apex and strongly tight in the dry state; they are lanceolate from 3 to 4 mm, very papillose-opaque in the upper 2/3 of the limb. The limbis a little curved at the edges, and terminates in small cap, more or less mucronate, with a vein that is not very excurrente; it has two bands of stereids. Cells in the upper limb have thin membranes and generally square cellular contours becoming rectangular and thick membrane towards the lower part. The thallus is clearly differentiated,intwo parts: that on the dorsal side is formed of a very green assimilative tissue, and that on the ventral side consists of a parenchyma little or not chlorophyllian, being used for retention or conduction of substances. The assimilative tissue is formed by chambers filled with chlorophyllous bristles (sometimes very short), and regularly drawn up on their floor, opening by pores.  (Werner, 1932); as well as along cracks on limestone rocks at Adar-Ouaman in the Anti-Atlas (Mayor & Werner, 1934). This messicole species according to Augier, 1966, has been described as a pioneer on argillaceoussoil and calcareous sand. According to Boulay, 1984, it is found on clay-sandy soil, on old walls owing to cracks and on limestone rocks. In Chellah, this species was collected on limerubble stone masonry or clay-sandy soil. Targionia hypophylla L. is a hepatic with a dark green thallus of 10 to 15 mm long and 4 mm wide. The thallus is clearly differentiated, in two parts: that on the dorsal side contains a very green assimilative tissue, and that on the ventral side consists of a parenchyma little or not chlorophyllian. The assimilative tissue is formed by chambers filled with chlorophyllous bristles regularly drawn up on their floor, closed or opening by pores. The ventral scales are large, and violet. The stomata are surrounded by 2 to 3 circles of cells very different from the epidermal cells. The capsule located on the ventral surface of the thallus is contained in a bivalve envelope. It contains elaters with 2-3 whorls and spores from 50 to 60 µmof diameter.  Jelenc, 1955a, 1967, Jovet-Ast, 1965, quoted by Ros et al., 1999);on mud of dried marshes (Augier, 1966, Boulay, 1984, Hamada et al., 2002. Riccia crystallina L. emend. Raddi, is a hepatic with radial sling thallus, with obtuse lobes, 1 to 4 mm wide, light green above, pale in lower part. The assimilative tissue is made of lacunary parenchyma. The thallus is one to two times dichotomous. The spores of 70 µm diameter on average carry on their convex face a network of alveoli. It is met with Sphaerocarpos michelii forming a same stand.

Family of Fossombroniaceae
Fossombronia angulosa (Dicks.) Raddi (Jungermannia angulosa Dicks.). In Morocco, it has been reported on different substrates: on siliceous soil, on siliceous soil at the edge of a stream; on soil covering rocks of granite, on fresh ground in the shade, on shady rocks partially covered with soil; or on siliceous red soil at the edge of a runoff (Jovet-Ast, 1956c). According to Augier 1966, this species has been reported on non-calcareous wet soil, on the slopes of hedges, paths and in rather dry places. It is cosmopolitan in the Mediterranean region according to Boulay, 1984. In Chellah, it is found between the rocks of the studied site. Fossombronia angulosa (Dicks.) Raddi, is a hepatic with leaves of 1-3/0.5 cm with a creeping stem bearing succubus leaves and purple rhizoids. The silk is short with a round capsule containing spores of about 40 μm. The spore has a hemispherical face and a pyramidal face.

Family of Sphaerocarpaceae
Sphaerocarpos michelii Bellardi (Sphaerocarpos terrestris (Micheli) J.E.Sm.). It has been reported on soil covering a granite rock (Jovet-Ast, 1956c); on sandy soil and on the granitic rock above the hot spring of Oulmès (Ahayoun et al., 2007). Augier, (1966) describes it as a messicoleand indicates its presence on clay soil. It was harvested on the clay-sandy soil of the studied site. Sphaerocarpos micheliiBellardi, is a dioecious hepatic with light green thallus with unistratified margins. Antheridia and archegones are located on the dorsal side of the thalli, each is surrounded by an involucre with the pyriform male and the globular female, tightened in the upper part and presenting a small opening. The dehiscence of the capsule is irregular. The spinous spores are united in tetrads of dark brown color measuring approximately 100 μm in diameter.

Bryophytes and Biodeterioration
Bryophytes are reviviscent plants that settle as soon as the substrate is moistened ( fig. 7 and 8); they can occupy very poor environments in organic matter. The samples were taken at different locations in Chellah site (Fig. 1). The obtained results show that bryophyte colonize both the moistenedsoil, the concrete of steps, the zellij, the terracotta brick made up essentially of calcarenite dating from antique and Islamic times ( fig. 9, 10 and 11). This rock was extracted from the quarries of Sidi Bou-Knadel, about ten kilometers to the north of Salé,from plioquaternary age and belonging to the dune cords that extend along the Atlantic coast between El Jadida and Larache. It is a compact, yellow-beige detritic sedimentary rock made up of two detrital fractions: a bioclastic fraction (shell fragments) and a terrigenous fraction composed of millimetric quartz grains bound by a limestone cement. According to the bioreceptivity criteria described by Guillite (1995), Salé calcarenite offers a set of characteristics favorable to biocolonization. Indeed, the surface quality of Salé calcarenite has a large roughness allowing the anchoring of rhizoids. This surface roughness is also associated with a high porosity of about 24% and an estimated capillarity of 12.37 (El Amrani El Hassani & El Azhari, 2009), which is conducive to retention of water and favorable for the installation and growth of bryophytes. . This is called physical biodeterioration.
Other chemical processes are involved: the dissolution of limestone substrate minerals by acidic secretions produced by plants as well as the assimilation of the substrate as a nutrient (Warscheid & Braams, 2000). This is referred to as a chemical biodeterioration.

V. CONCLUSION
The archaeological site of Chellah has been subject to few scientific researches in botanical matter, in particular with regard to the bryophytes. Therefore, our objective consists in describing and identifying the species of bryophytes present in this site and then to establish a list of taxaof these species. The harvest of the bryophytes allowed us to identify 20 species distributed as follows: -Fourteen species belonging to the Moss class divided into 5 orders and families and 13 genera, the most widely represented order being the Pottiales with Fissidens bryoides, the most widespread species in the site; -Six species belonging to the Hepatic class including one leaf hepatic. They are distributed in 3 orders, 5 families and genera, with Lunularia cruciata, the most encountered species. The colonization of archaeological materials by bryophytes leads to their aesthetic, physical and chemical biodeterioration due to the acid secretions produced by these plants. All these processes have an important role in pedogenesis and thus in the initiation of plant succession. This fact, without gravity in the natural environment, becomes a source of issues when it concerns materials used in historical monuments whose durability is then threatened.