186 IAWAIAWA Journal Journal 35 (2), 35 2014: (2), 2014 186–198
Comparative wood anatomy of Juniperus from Macaronesia
Paloma de Palacios1,*, Luis G. Esteban1, Francisco G. Fernández1, Alberto García-Iruela1, María Conde2 and Elena Román-Jordán1 1Universidad Politécnica de Madrid, Escuela Técnica Superior de Ingenieros de Montes, Departamento de Ingeniería Forestal, Ciudad Universitaria s/n, 28040 Madrid, Spain 2CIFOR-INIA, Departamento de Productos Forestales, Carretera de la Coruña Km 7.5, 28040 Madrid, Spain *Corresponding author; e-mail: [email protected]
ABSTRACT The wood anatomy of the three species of Juniperus occurring in Macaronesia is compared for the first time using representative samples of each species collected in its natural region of provenance: J. cedrus Webb & Berthel and J. phoeni- cea L. var. canariensis Guyot, in the Canary Islands, and J. brevifolia (Seub.) Antoine, in the Azores. The three species are anatomically similar, although some qualitative differences were observed: distribution of axial parenchyma very scarce in J. phoenicea compared with the other two species, presence of crassulae only in J. phoenicea, presence of torus extensions and notches on pit borders in the radial walls of J. brevifolia, and ray parenchyma end walls slightly nodular in J. cedrus as opposed to very nodular in J. phoenicea and J. brevifolia. In addition, the biometry of tracheid pit diameter in the radial walls, ray height in number of cells, and largest and smallest diameters of cross-field pits shows differences for a significance level of 95%. Keywords: Azores, Canary Islands, Juniperus brevifolia, Juniperus cedrus, Juniperus phoenicea var. canariensis.
INTRODUCTION
The genus Juniperus includes 52 species, 10 subspecies and 43 varieties distributed in the northern hemisphere from the subarctic tundra to the semi-desert, except J. procera, which is found south of the equator, in the east and south of tropical Africa (Farjon 2005). Macaronesia is home to three species: two in the Canary Islands (J. cedrus Webb & Berthel and J. phoenicea L. var. canariensis Guyot) and one in the Azores (J. brevifolia (Seub.) Antoine). Juniperus phoenicea var. canariensis occurs naturally in the Canary Islands on Tenerife, La Palma, El Hierro, Gran Canaria and La Gomera, normally below an altitude of 1000 m (Bramwell 1990). Adams et al. (2010a) considered that this species should be called Juniperus phoenicea var. turbinata because of its similarities to the species found in Morocco, even though the terpenoids in the oils of the Canary Islands species
© International Association of Wood Anatomists, 2014 DOI 10.1163/22941932-00000059 Published by Koninklijke Brill NV, Leiden
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Figure 1. – A: Juniperus brevifolia, Fayal (The Azores). – B: J. cedrus, La Palma (Canary Is- lands). – C: J. phoenicea var. canariensis, El Hierro (Canary Islands). do not correspond to either of the varieties specified for this species (var. turbinata and var. phoenicea). Juniperus brevifolia is endemic to the Azores, where it occurs on the islands of Corvo, Faial, Flores, Pico, Santa Maria, São Jorge, São Miguel and Terceira, normally at altitudes from 240 to 800 m, although some individuals are found from sea level to 1500 m. These two species are normally shrubs or small trees, usu-
Downloaded from Brill.com10/08/2021 12:50:50PM via free access 188 IAWA Journal 35 (2), 2014 ally branched from the base, with a height of up to 8 m. Juniperus cedrus, however, is capable of reaching tree heights of 15 m. Its distribution range is the islands of Tenerife, La Palma and Gran Canaria, although it has also been cited from Madeira (Fig. 1). Cavaleiro et al. (2001) studied the essential oils of the J. cedrus population in Madeira and concluded that they differed from the oils studied in the same species in the Canary Islands. Adams et al. (2010b) also considered that this Juniperus should be regarded as separate from J. cedrus and be called Juniperus maderensis, based on the volatile leaf oil composition and the DNA sequence data. The aromatic and decay-resistant nature of the wood of these three species has led to a decline in their numbers over the centuries through overharvesting. The IUCN Red List of Threatened Species includes J. cedrus as “endangered” (Rumeu Ruiz et al. 2011) and J. brevifolia as “vulnerable” (Thomas 2011). Studies on the anatomy of these species are very scarce. Moreover, in some cases samples were taken from branches, and other studies do not specify the origin of the samples. Greguss (1972) described J. brevifolia, using a sample of a 9-year-old branch sent by H. Gaussen from the Forest Laboratory in Toulouse, and J. cedrus, using a single sample from Kew Gardens, London. Peraza and López (1967) studied J. cedrus and J. phoenicea var. canariensis from a single provenance (La Gomera), but did not speci- fy the size of the sample or compare the anatomy of the two species. Esteban et al. (2009a) did not describe the anatomy of J. cedrus and J. phoenicea var. canariensis, although they applied artificial neural networks for the first time as a tool for identifying the wood of species with very similar structure, obtaining accuracy percentages of 92% in the differentiation of these species. Their study will enable hypotheses to be proposed about wood and charcoal remains found at archaeological sites in both archipelagos and also about the palaeogeography of these species. A complete description of the wood of the three Macaronesian species, isolated for thousands of years in these Atlantic archipelagos, combined with a comparison through representative sample collections, would complement recent molecular phylogenetic studies on Juniperus in general (Mao et al. 2010) and more specifically on Juniperus in Macaronesia (Adams et al. 2010a, b; Rumeu et al. 2011). This study describes the wood anatomy of the three species of Juniperus in Maca- ronesia, defines their biometry, and determines whether the three species show differ- ences that will make it possible to differentiate them with qualitative and/or quantitative attributes. MATERIAL AND METHODS The samples were collected in the natural forests of the three species: Juniperus cedrus was collected only on the island of La Palma because of its level of protection; J. phoenicea var. canariensis on the islands of La Palma, la Gomera and El Hierro; and J. brevifolia on the island of Faial, from two areas of provenance, one at an altitude of approx. 70 m in the municipality of Castelete and the other in the area of Lagoa Do Capitao, at an altitude of 838 m. In each zone, five trees more than 70 years old and representative of the forest were felled, excluding compression wood. To locate the Canary Islands forests, the publication
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Figure 2– 8. Transverse sections. – 2: Sapwood and heartwood distinct (Juniperus brevifolia). – 3: Growth ring boundaries distinct (J. brevifolia). – 4: Abrupt transition from earlywood to latewood (J. brevifolia). – 5: Latewood only a few cells thick (J. phoenicea var. canariensis). – 6: Axial parenchyma diffuse and tangentially zonate (J. brevifolia). – 7: Intercellular spaces (J. phoenicea var. canariensis). – 8: Tracheid pits in tangential wall on growth ring boundary (J. phoenicea var. canariensis). — Scale bars for 3 & 6 = 250 μm; for 4 & 5 = 200 μm; for 7 & 8 = 100 μm.
Downloaded from Brill.com10/08/2021 12:50:50PM via free access 190 IAWA Journal 35 (2), 2014 by Ceballos and Ortuño (1951) was used, and in the Azores, assistance was provided by the forest services of the island of Faial. Microscope slides were prepared following the usual methods of softening, section- ing, staining and mounting. Samples were observed without staining and stained with safranine for lignified cell walls and Sudan 4 for resin (Jane 1970). A Leica DM2500 light microscope with a DFC 420 camera was used, as well as image processing software IM50 v.5 release 220 and scanning electron microscopy (SEM) mod. JEOL JSM-6380. The anatomical descriptions were made in accordance with the IAWA Committee (2004). The biometry was conducted in three slides prepared from each tree, in all cases in mature wood, from a disc obtained 50 cm from the ground, between rings 70 and 100, using the WinCell image analysis programme. From each slide the following measure- ments were taken: 25 measurements of axial tracheid length and diameter, ray height (µm and number of cells), and number of pits per cross-field in the earlywood; 50 measurements of tracheid pit diameter and largest and smallest cross-field pit diameter in the earlywood; and five measurements of the number of rays per mm2. Tracheid length was measured following Ladell’s indirect method (Ladell 1959), ray frequency was measured in five different areas of one square millimetre on the tangential section. The standardised skewness and standardised kurtosis statistics were used to study normality and the ANOVA test was applied to analyse the samples and study the level of significance of the variables measured at species level. To determine the significant differences between species, multiple rank tests and LSD tests were applied using the ANOVA data, considering each species globally, without taking into account the different provenances in the cases of J. phoenicea and J. brevifolia. The study of the values of ray height in number of cells was performed using the frequency histogram and therefore the most frequent value does not correspond to the mean value but to the most frequent ray height. Statistical calculations were made with the Statgraphics Centurion Ver. 15.2 programme, for a 95% significance level.
RESULTS Anatomical description General features — The wood of all three species is aromatic and the sapwood and heartwood are markedly different in colour: the sapwood is yellowish and the heartwood is reddish brown (Fig. 2). Transverse section — Resin canals absent and growth ring boundaries distinct (Fig. 3), frequently lobed, as is the trunk. Abrupt transition from earlywood to late- wood (Fig. 4), generally with much thinner latewood, particularly in J. phoenicea var. canariensis, where it is sometimes only one or two cells wide (Fig. 5). Axial parenchy- ma present, very abundant in J. cedrus and J. brevifolia, diffuse and tangentially zonate, with dark coloured cell content (Fig. 6). Quite sparse in J. phoenicea, generally dif- fuse and tangentially zonate, only one cell wide. Tracheids polygonal in outline, from rectangular to hexagonal, with intercellular spaces (Fig. 7). Tracheid pits in tangential walls, generally in tracheids near the growth ring boundary (Fig. 8).
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Figure 9–12. Tangential sections. – 9: Wood rays very low, 2–3 cells high (Juniperus brevifolia). – 10: Transverse end walls of axial parenchyma cells nodular (J. brevifolia). – 11: Axial paren- chyma with dark coloured cell content (J. brevifolia). – 12: Tracheid pits in tangential walls (J. phoenicea var. canariensis). — Scale bars for 9 & 12 = 150 μm; for 10 = 15 μm; for 11 = 50 μm.
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Figure 13–20. Radial sections. – 13: Cross-field pits cupressoid, 1–2 per fieldJuniperus ( cedrus). – 14: Tracheid pits in radial walls predominantly uniseriate (J. phoenicea var. canariensis). – 15: Two seriate tracheid pits scarce, in opposite arrangement (J. phoenicea var. canariensis). – 16: Crassulae (J. phoenicea var. canariensis). – 17: Torus extensions (te) and notched borders (nb) (J. brevifolia). – 18: Smooth horizontal walls (J. phoenicea var. canariensis). – 19: End walls slightly nodular (J. cedrus). – 20. Nodular end walls and indentures (J. phoenicea var. canariensis). Scale bars for 13 & 18 = 15 μm; for 14 = 50 μm; for 15–17 & 19 = 25 μm; for 20 = 10 μm.
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Figure 21 & 22. SEM. – 21: Warty layer (Juniperus brevifolia). – 22: Transverse end walls of axial parenchyma cells nodular (J. brevifolia).
Tangential section — Homogeneous rays up to 19 cells high in J. phoenicea var. canariensis from La Palma, although the most frequent ray height is 2–3 cells (Fig. 9). Rays almost exclusively uniseriate. Few biseriate rays only regularly observed in J. cedrus, less than 10% of the total. Transverse end walls of axial parenchyma cells nodular (Fig. 10 & 22) and with dark coloured cell content (Fig. 11). Tracheid pits in tangential walls, of smaller diameter than pits in radial walls, arranged in uniseriate rows in the latewood (Fig. 12). Warty layer present in all three species, although visible only with SEM (Fig. 21). Radial section — Axial tracheids without helical thickenings. Ray tracheids absent. Cross-field pits cupressoid, 1–2 per cross-field (Fig. 13). Tracheid pits in radial walls pre- dominantly uniseriate (Fig. 14), very rarely two-seriate in opposite arrangement in J. phoenicea var. canariensis (Fig. 15). Crassulae abundant in J. phoenicea (Fig. 16). Tracheid pits with torus extensions and notched borders in J. brevifolia (Fig. 17). Ray parenchyma cells with smooth horizontal walls (Fig. 18) and nodular end walls (Fig. 20); in J. cedrus end walls are slightly nodular (Fig. 19). Indentures present (Fig. 20).
Comparison of the three species from the qualitative point of view shows greater abundance of axial parenchyma, both diffuse and tangentially zonate, in J. cedrus and J. brevifolia, compared with J. phoenicea; presence of crassulae in all the samples of J. phoenicea studied and absence in the other two species; presence of torus extensions and notches in all the samples of J. brevifolia and absence in the other two species; and ray parenchyma end walls slightly nodular in J. cedrus, compared with very nodular end walls in J. phoenicea and J. brevifolia.
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Biometry The biometry of the species studied is shown in Table 1. The diameter of the tracheid pits in the radial walls, ray height in number of cells and the cross-field pit diameters show statistically significant differences between the three species.
DISCUSSION
Gaussen (1968) established that the genus Juniperus presents such high homogeneity that its species cannot be differentiated. Earlier, Jacquiot (1955) came to the conclu- sion that they could be distinguished only through their biometry. Other authors, however, affirmed that certain species could be differentiated on the basis of their anatomy. Examples include Phillips (1948) and Brown et al. (1949), who separated J. virginiana and J. lucayana from the other Juniperus species based on the presence of nodular end walls in the wood rays. However, Ter Welle and Adams (1998), in their study on American Juniperus species, subsequently confirmed that they could not be distinguished through their wood anatomy. Even at the genus level differentiation presents major difficulties. Although Phillips (1948) stated that Juniperus could be distinguished from other woods by the abundance of axial parenchyma with nodular transverse end walls and its cupressoid cross-field pits, this must be interpreted with some caution, as several Cupressaceae genera also show these features, e.g., Fitzroya, Fokienia and Glyptostrobus. It is likely that one of the few ways to distinguish such anatomically similar species is through artificial neural networks (ANN), as in the study by Esteban et al. (2009a). The three species studied have a peculiar cedar-like odour, as described by Phillips (1948) and commonly associated with pencils, although Cupressus and Cedrus have a similar odour, making it difficult to differentiate them from these genera. Adams (1991) stated that the oils of J. ashei, J. virginiana and Cupressus funebris are virtu- ally identical. Kukachka (1960) considered that two clearly differentiated groups could be estab- lished in Juniperus through the heartwood colour. Peraza and López (1967) considered that J. cedrus heartwood was somewhat darker than in J. phoenicea, but the nuances of colour in this case are so slight that differentiation is impossible. As with the other Juniperus species, the samples studied are characterised by the absence of resin canals and helical thickenings and the presence of homogeneous rays, abundant axial parenchyma with frequently nodular transverse end walls and cupressoid cross-field pits. These features are very similar to other Cupressaceae genera. In the growth rings an abrupt transition from earlywood to latewood is observed, although in the case of J. phoenicea var. canariensis only one or two rows of latewood tracheids are seen (Fig. 5). However, this feature should not be taken into account to differentiate these species, as it is climate dependent (Core et al. 1979). No organic deposits were observed in the tracheids, even though they have been cited in other species of the genus, e.g., Juniperus procera (IAWA Committee 2004). The three species have a warty layer that is visible with scanning electron micros- copy. As in Pinaceae and particularly in Abietoideae (Esteban et al. 2009b), tracheid
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Table 1. Biometry of the wood of Juniperus species from Macaronesia.
Feature J. cedrus (*) J. phoenicea var. canariensis (*) J. brevifolia La Palma La Palma La Gomera El Hierro Faial Faial [Mean value ± SD (Castelete) (Lagoa Do and range (min-max)] Capitao)
Diameter (μm) 27.2±4.7a 26.7±3.6 25.8±3.5 30.4±5.4 26.2±4.14 27.5±4.7 (17.2-39.3) (18.2-39.3) (16.5-38.3) (17.4-48.0) (15.3-39.5) (15.3-38.4) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 27.6±4.7a (16.5-48.0) 26.8±4.5a (15.3-39.5)
Length (mm) 2.7±0.9a 2.1±0.8 2.4±0.5 3.3±0.9 2.3±0.7 2.2±0.5 (1.3-9.0) (1.0-5.7) (1.4-4.9) (1.7-7.0) (1.4-4.5) (1.3-3.5) –––––––––––––––––––––––––––––––––––– ––––––––––––––––––––
racheids 2.6±0.9a (1.0-7.0) 2.3±0.6b (1.3-4.5) T
Diameter tracheid 15.4±1.6a 12.5±1.4 13.5±1.5 14.6±2.4 14.5±2.5 14.3±1.8 pits (μm) (11.3-19.8) (8.6-17.9) (9.9-18.8) (9.9-22.6) (9.5-18.8) (11.6-19.8) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 13.5±2.0b (8.6-22.6) 14.4±2.2c (9.5-19.8)
Height (μm) 70.3±38.0a 73.0±45.9 55.8±27.4 58.3±33.1 56.7±23.6 69.8±42.1 (15.4-314.7) (13.4-352.9) (14.4-275.1) (12.5-277.1) (19.2-202.4) (19.2-270.4) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 62.1±36.8b (12.5-352.9) 62.8±34.2b (19.2-270.4)
Most common 2a (***) 2 2 2 3 3 height in no. of (1-17) (1-19) (1-14) (1-18) (1-10) (1-15) ays
R cells and range (**) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 2b (1-19) (***) 3c (1-15) (***)
Number of 65.1±7.5a 60.0 ± 6.6 65.2 ±10.8 63.8 ± 6.3 87.6 ± 9.3 78.5 ±16.4 rays /mm2 (49-82) (48-83) (44-90) (47-80) (72-102) (52-97) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 63.0±8.4a (44-90) 83.0±13.9 (52-102)b
Largest diameter 6.4± 0.8a 5.1± 0.8 5.1± 0.7 4.8 ± 0.7 6.1± 0.8 5.4 ± 0.7 cross-field pits (4.2-10.3) (2.7-8.0) (3.1-7.3) (2.8-6.9) (4.3-8.0) (3.7-8.2) ( μm) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 5.0 ± 0.7b (2.7-8.0) 5.7± 0.8c (3.7-8.2)
Smallest diameter 3.2± 0.5a 2.6 ± 0.5 2.2 ± 0.4 1.8 ± 0.3 2.8 ± 0.4 2.5 ± 0.6 cross-field pits (2.0-5.2) (1.0-5.0) (1.3-4.0) (1.0-2.7) (1.6-4.0) (1.2-3.9) ( μm) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 2.2 ± 0.5b (1.0-5.0) 2.7± 0.5c (1.2-4.0)
Number of pits 1.7± 0.8a 1.7± 0.8 1.9 ± 0.9 2.2 ± 0.9 1.7± 0.8 1.7± 0.7 Cross-fields pet cross-field (1-4) (1-4) (1-4) (1-5) (1-4) (1-4) –––––––––––––––––––––––––––––––––––– –––––––––––––––––––– 1.9 ± 0.9b (1-5) 1.7± 0.7a (1-4)
Most frequent num- ber of pits per 1 1 2 2 1 1 cross-field2
(*) Esteban et al. 2009a. – (**) Most frequent ray height values calculated from the frequency histogram. – (***) The analysis of the statistically significant differences for ray height is performed by considering the data separately, without taking the frequency histogram into account. Different superscript letters indicate statistically significant differences between species, considering each species globally and without taking the different provenances into account, with a confidence level of 95%. Groupings a, b and c were obtained from the LSD and multiple range tests.
Downloaded from Brill.com10/08/2021 12:50:50PM via free access 196 IAWA Journal 35 (2), 2014 pits appear in the tangential walls of the tracheids in the latewood. Torus extensions and notched borders are observed on the tracheid pits in the radial walls of J. brevifolia. This observation concurs with Willebrand (1995), who noted the sporadic presence of extensions in Juniperus spp. and notched borders in J. thurifera. The presence of these features restricted to the samples of J. brevifolia could be used as a diagnostic value to differentiate this species from the other two. Although the distribution of the axial parenchyma is similar in the three species, the small number of parenchyma cells in J. phoenicea, compared to the other two spe- cies, is obvious. As regards the transverse end walls, their shape is similar to those described in other species of Juniperus, from slightly nodular to very nodular, as in Juniperus thurifera (Esteban et al. 1996), to slightly pitted (Jacquiot 1955) or pitted or nodular (Phillips 1948; Kukachka 1960; Ter Welle & Adams 1998; IAWA Com- mittee 2004). The wood rays are homogeneous, with smooth horizontal walls. The end walls are very nodular in J. phoenicea and J. brevifolia and slightly nodular in J. cedrus. The pres- ence of indentures concurs with those observed by Kukachka (1960) for the Juniperus genus in general, and with Greguss (1972) for J. cedrus and J. brevifolia in particular. Although the anatomy of the three species is very similar, certain features such as the scarce parenchyma in J. phoenicea, the presence of crassulae only in J. phoenicea, and in particular the presence of torus extensions and notches in pits in the radial walls of J. brevifolia and slightly nodular ray parenchyma end walls in J. cedrus could be used to differentiate between the three species. In terms of the biometry of the species, it can be stated that the diameter of the tracheid pits in the radial wall, ray height (number of cells), and largest and smallest cross-field pit diameters show significant differences for a significance level of 95%. Other features such as tracheid length, ray height (µm), number of rays per square millimetre and number of pits per cross-field make it possible to establish significant differences in one of the species compared to the other two (Table 1). The anatomical similarity of these three species may possibly be associated with their close phylogenetic affinities, which was studied by Adams (2000). Comparative anatomy of all the species of the genus Juniperus would make it possible, both in this genus and in many other conifer genera, to clarify matters when differentiating such phylogenetically close species through their anatomy, although any study must be conducted with samples collected in their regions of provenance and using mature wood.
ACKNOWLEDGEMENTS
The authors are grateful to the forest services of the islands of La Gomera, La Palma and El Hierro, in the Canary Islands, and of the island of Faial, in the Azores, for their collaboration in sample col- lection. This study is part of the AGL2004-02528 Project of the Spanish National Plan for Scientific Research, Development and Technological Innovation, funded by the Spanish Ministry of Education and Science and the European Regional Development Fund (ERDF).
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Accepted: 2 November 2013
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