
recorded the presence of numerous small vessels, solitary, in radial multiples of 2-3, ring and semi-ring porous, occasionally with helical thickenings, simple perforation plate, alternate intervascular pits, very small, members of vessels of medium length to moderately long, are typical features. Very weakly defined vestures were seen in Celastraceae (Archer and Van Wyk, 1993a) .

Rays are described in some genera to be exclusively uniseriate and homogeneous, in other heterogeneous multiseriate (3-4).

Maytenus is a genus of temperate and warm regions of South Asia (Yemen, Malaysia and Thailand), Africa (Canary Islands, northwest and northeast Ethiopia, and South Africa), and America from Mexico to Tierra del Fuego. It grows in a variety of climates, from tropical (77 sp. in Brazil) to subpolar (Hurrel and Bazzano, 2003) .

In Argentina the Genus Maytenus comprises about eleven native species. Three are endemic shrubs and small trees (Boelke, 1992) , distributed in the subtropical wet forest of Misiones, Yungas, Chaco semiarid forest and Patagonian Andean temperate forests (Zuloaga and Morrone, 1999) .

Maytenus boaria (Maitén) is the most important tree of Patagonian Andean forests (Lourteig and Odonell, 1955) . The species is used as a natural dye and its branches are an important source of foliage for sheep in the steppe (Tortorelli, 2009). M. spinosa, M. viscifolia and M. vitis- idaea are species of the semiarid forest of the Chaco region. They are indicative of saline soils and semiarid areas. Giménez and Hernández (2008) found M. spinosa in 50% of the areas studied in Santiago del Estero, Province, M. vitis-idaea in 36% of them, and M. viscifolia at only one site (Sierras de Guasayan). Their uses include dye, fodder, food and to a lesser extent, as timber depending on the size of their trunks (Giménez et al., 2010) . M. cuezzoi is a threatened endemic species (Cat. 5: restricted distribution plant and sparse populations with restricted distribution and sparse populations).

For the genus Maytenus, the outstanding features of the wood are: diffuse porous, small vessels, very numerous (20-40), solitary and in radial multiples, and sometimes helical thickenings. Axial parenchyma is very variable in type and number, commonly scattered or absent, diffuse and multiseriate or thin bands (Metcalfe and Chalk, 1983) . Vessels with helical thickenings were cited M. boaria (Tortorelli, 2009 ).

Rays are heterogeneous, frequently with 2-4 vertical rows of cells, 1 to 3 seriate, less than 12/mm (Metcalfe and Chalk, 1983) ; M. boaria (-9 ray/mm) with 3-4 seriates (Tortorelli, 2009 ).

Mechanical tissue is composed of fibre with distinctly bordered pit (fibre-tracheids), numerous, occasionally septate fibres with simple pits, of medium length, sometimes with helical thickenings (Metcalfe and Chalk, 1983) . Is characterized by fibres dimorphic (bands of thick-walled fibres with bordered pits alternating with septate and thin-walled fibres with minutely bordered pits), resembling the axial parenchyma (Joffily et al., 2007) .

Fibres with distinctly bordered pits were cited in M.

boaria (Tortorelli, 2009) , M. acuminata (Metcalfe and Chalk, 1950) , M. micrantha (Detienne and Jacquet, 1983) .

Fibre-tracheids are elements of transition between tracheids and fibres. They are characterized by the presence of bordered pits, generally located in the radial walls, present in Apocynaceae, Celastraceae (some Genera) Myrtaceae, Sapotaceae, Zygophyllaceae among others. Carlquist (1988) described the imperforate tracheal elements of Catha, Elaeodendron, Celastrus and Maytenus as septate libriform fibres, septate fibre-tracheids and vasicentric tracheids.

Fibre-tracheid has been cited as an adaptive strategy in species of arid and semiarid areas, such as Aspidosperma quebracho-blanco (Apocynaceae) (Moglia et al., 2009) ; Monttea aphylla (Scrophulariaceae) ; Tabernaemontana catharinensis (Apocynaceae) (Giménez, 2004) . Carlquist and Hoekman (1985) cite the presence of fibre-tracheids as typical element of the arid flora of California.

Several African species have been described anatomically: M. acuminata (Metcalfe and Chalk, 1950) ; M. micrantha (Detienne and Jacquet, 1983) , M. senegalensis (Neumann et al., 2000) . Perforated ray cells (PRC) are present in the stem xylem and in the roots of M. brasiliensis and M. obtusifolia (Joffily et al., 2007) . Sokal and Rohlf (1981) 
MATERIAlS ANd METhodS
The (Legname, 1973) . The plant is an indicator of saline soil, and the wood produces a dark reddish dye used to color wool, yarn, etc. (Giménez et al., 2007) . It is used as food for bees and farm animals, especially for goats at all times of year (Karlin, et al. 2010) . The ash obtained from burning wood is used as salt for human consumption.
MATERIAlS ANd METhodS
It also has anti-inflammatory, disinfectant, astringent and ophthalmic uses. The chewed leaves are used to cure diseases of the mouth (Giménez et al., 2010) . Maytenus spinosa (Griseb.) Lourteig & O´Donell (abriboca) is an endemic shrub with spiny branches and leathery leaves. It is native to Argentina and Uruguay (Digillio and Legname, 1966) . The bark produces a pink brown dye (Stramiglioli, 2007) . Legname (Legname, 1973; 1982) is an endemic unarmed tree, 3 m -7 m tall and 0,25 m. in diameter at the base, with entirely glabrous pale green Mature wood samples were fixed in 70% alcohol.
Maytenus cuezzoi
Transverse, radial and tangential sections (12 μ-18 μ thick) were cut using a sliding microtome. The sections were doubly-stained with 1% fuchsin and astra blue (Roeser, 1972) and mounted permanently by Entellan. Wood material was macerated following Jeffrey's method (Johansen, 1940) .
Maytenus cuezzoi
Terminology and determination of quantitative features follow the recommendations of the IAWA Committee (1989) and Tortorelli (2009) . For vessel diameters, vessel element lengths, fibre lengths and ray height, 25 measurements were taken from each specimen and averaged.
Maytenus cuezzoi
The influence of environmental conditions on characteristics (vessel diameter and vessel number) associated with water conduction was evaluated through the vulnerability index. The vulnerability index (VI) was calculated to estimate susceptibility to damage during water conduction of wood, as proposed by (Carlquist, 1988) : Non parametric analysis of variance (ANAVA) for repeated measures (Cody and Smith, 1991) and the Kruskal Wallis test (α = 0,05) was performed for 7 variables.
Maytenus cuezzoi
Professional Program InfoStat was used for statistical analysis (INFOSTAT, 2008) .The photomicrographs were taken with Zeiss Axiostar microscope and Sony video camera ExwaveHAD. Small blocks cut to produce transverse, radial and tangential surfaces were used for scanning electron microscopy (SEM).
RESUlTS

Anatomical descriptions
Maytenus vitis-idaea ( Fig. 1-8 Note: the scale corresponds to 100 um, except in the SEM micrographs which have included its own scale. Maytenus cuezzoi (Fig. 21-30) Growth rings distinct, marked by thick-walled fibres.
Anatomical descriptions
Wood diffuse-porous, rarely appearing semi-ring-porous. Maytenus spinosa (Fig. 31-36) Growth rings distinct, marked by thick-walled fibres.
Anatomical descriptions
Wood diffuse-porous, rarely appearing semi-ring-porous. The most important anatomical features are summarized in Table 1 Figures. From PCA, factor 1 expresses 58% of the variability, 33% factor 2 and 0,06 factor 3 ( Table 2 ). Factor 1 is considered practically significant, as explaining an important amount of the variability in the data. The variables that load significantly in Factor 1 are: vessel diameter (Vd), fibre length (Fl), and ray width (Rw); on Factor 2: vessel length (Vl), ray height (Rh), and fibre wall (Fw) load significantly. The species separate into different quadrants (Fig. 37) . 11.7 (7-16) S: 2.5 13.5 (9-18.5) S. 
M. spinosa and M. vitis-idaea have wide prevalence of solitary vessels (75%). This character is mentioned for
M. acuminata (Metcalfe and Chalk, 1983) , M. micrantha (Detienne and Jacquet, 1983) , and M. senegalensis (Neumann et al., 2000) . Vessel multiples of 2-3 is present in M.
M. spinosa and M. vitis-idaea have wide prevalence of solitary vessels (75%). This character is mentioned for
cuezzoi. M viscifolia exhibits vessels of all types including multiples of 2-5. (35,6 μm).
M. spinosa and M. vitis-idaea have wide prevalence of solitary vessels (75%). This character is mentioned for
Vessel elements are extremely short (<350 μ), especially in M. vitis-idaea and M. spinosa. Bailey (1957) and Baas (1982) believed that the length of vessel elements and other morphological characters, such as perforation plates and types of pits, reflect the level of specialization of a taxon and further recognized the evolutionary trends of vessel element lengths within angiosperm taxa which came to be known as Baileyane trends. Metcalf and Chalk (1983) also stated that the vessel element length is more significant as a measure of phylogenetic specialization than as a diagnostic character for a taxon. It is the general opinion of Bailey (1957) , Baas (1982) and Metcalfe and Chalk (1983) that the less specialized plant taxa have longer vessel elements than the specialized forms. This means high specialization of vessels elements in Maytenus.
M. spinosa and M. vitis-idaea have wide prevalence of solitary vessels (75%). This character is mentioned for
The vessel frequency show highly significant differences between species; they are extremely numerous in M.
spinosa; numerous in M. cuezzoi, M. viscifolia and M. vitis-idaea.
Vessels with helical thickenings were cited M. boaria (Tortorelli, 2009 ) and in M. cuezzoi, and vestured pits were observed in M. cuezzoi y M. viscifolia.
spinosa; numerous in M. cuezzoi, M. viscifolia and M. vitis-idaea.
The vulnerability index predicts which species can live in arid (Carlquist, 1988) . Xylem efficiency depends on the diameter and frequency of vessels in a given area. In arid regions, wood must support high negative pressures. In these regions, the morphology of vessels has adaptive value. There is a reduction of vessel diameter and length, increase in vessel frequency and degree of clustering, and presence of qualitative anatomical features, such as simple perforations. These adaptations increase safety against embolisms (Lindorf, 1994) . Baas and Carlquist (1985) emphasize the presence of the following characters in xerophytes and halophytes: small vessels (29-53 μ), high vessel frequency (92-150), semi-ring porous, and presence of fibre-tracheids. All of these features (except porosity) are present in the species studied. The anatomical structure of the woods of this study is characteristic of species of arid zones, such as the dry Chaco region in which Maytenus is common. The smaller diameter and length of the vessels, and their high frequency, are some of the most notable features of the conductive elements. They are considered signs of adaptation to extreme aridity and tend to increase the safety, given the limited amount of water available (Lindorf, 1994; Carlquist, 1988; Moglia and Giménez, 1998; Giménez, 1993; Roth and Giménez, 1997; Roth and Giménez, 2006 
Conclusions
The species studied show the anatomical features typical of genus Maytenus.
Conclusions
The anatomical structure of the woods of this study is characteristic of species of arid zones.
Conclusions
The smaller diameter, shorter vessels and high frequency, are the most notable features of the conductive elements, considered signs of adaptation to extreme aridity 

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