STRUCTURAL VARIATIONS IN ROOT AND STEM WOOD OF - Brill
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IAWA Journal, Vol. 28 (2), 2007: 173-188
STRUCTURAL VARIATIONS IN ROOT AND STEM WOOD OF
STYRAX (STYRACACEAE) FROM BRAZILIAN FOREST
AND CERRADO
Silvia Rodrigues Machado 1*, Roberto Antonio Rodella 1, Veronica Angyalossy 2
and Carmen Regina Marcati 3
SUMMARY
The genus Styrax L. (Styraeaeeae) has a wide distribution in Brazil, oe-
eurring in diverse eeosystems. To get a better insight into the eeologieal
adaptations ofwood strueture, we studied two speeies, S. camporum and
S.jerrugineus from the eerrado, and three speeies, S. latifolium, S. martii
and S. leprosus from the Atlantie forest. For eaeh speeies, the wood of root
and stern was analyzed separately and observations inc1uded qualitative
as weIl as quantitative wood eharaeteristies. The results show that there
were signifieant anatomical differenees between the forest and eerrado
speeies as weIl as between the root and stern wood within single spe-
eies. Quantitatively, the most informative features in the root wood that
separated the forest from the eerrado speeies were diameter, length and
number of vessels, length of fibres, and width and frequeney of rays. In
the stern wood, length and frequeney of vessels, length of fibres, and
width and frequeney of rays were the most informative features. In eon-
trast to the forest speeies, whieh had larger vessel diameters in their stern
wood, the eerrado speeies had larger vessel diameters in their root wood.
The ea1culated vulnerability index indieates that all Styrax speeies have
adaptations to mesie eonditions. The eerrado speeies had the smallest
index values, whieh eould be related to the seasonally dry eondition of
this environment.
Key words: Styrax, Styraeaeeae, wood anatomy, root, seeondary xylem,
stern.
INTRODUCTION
Styraeaeeae eonstitute a dieotyledon family best known by the indumentum of stel-
late or seale-like hairs and for the produetion of benzoin (gum benzoin) and storax.
I) Departamento de Botänica, Instituto de Biociencias, Universidade Estadual Paulista, Botucatu,
SP, CP 510, CEP 18618-000, Brazil.
2) Departamento de Botänica, Instituto de Biociencias, Universidade de Sao Paulo, SP, CP
11461, CEP 05422-970, Brazil [E-mail: vangyalossy@ib.usp.br].
3) Departamento de Recursos Naturais - Ciencias Florestais, Universidade Estadual Paulista,
Botucatu, SP, CP 237, CEP 18603-970, Brazil [E-mai!: carmen@fca.unesp.br].
*) Corresponding author [E-mai!: smachado@ibb.unesp.br].
Associate Editor: Steven Jansen
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The family occurs in relatively warm parts of the world, such as the Mediterranean,
eastem Asia, the Malay Archipelago and parts of North and South America. In tropical
Africa it is represented by only one genus (Metcalfe & Chalk 1950; Hutchinson 1973;
Spongberg 1976).
Styrax L. is by far the largest and most widespread of the 11 genera, including about
130 out of the total of c. 160 species which comprise the family Styracaceae. The genus
has a widespread but disjunct distribution, occurring in the Americas, eastem Asia,
and the Mediterranean. More than half of the number of the species occurs in South
America, where they are distributed among a wide array ofhabitats, including the low-
land rainforest, montane rainforest, subparamo, tepui scrub, restinga, rocky grasslands,
and cerrado (Nakajima & Monteiro 1986; Fritsch 2001).
In Brazil, the genus Styrax comprises about 25 species (Nakajima & Monteiro 1986)
and occurs as shrubs and small trees in the cerrado (a savanna -like ecosystem), and
as tall trees in semi-deciduous seasonal forest of southeastem Brazil (Flaster 1973).
Although both ecosystems are characterized by seasonal rainfall with dry relatively
cool winters, the cerrado typically has the most strongly seasonal climate with distinc-
tive wet and dry seasons. Moreover, forest soils are shallow, high in organic material
and predominantly composed of clay, while soils of the cerrado are deep and weil
drained, sandy, acidic, extremely low in available nutrients and include high levels of
soluble Al, resulting in the typical xeromorphic appearance of its vegetation (Franco
2002).
Reports about ecological wood anatomy have been conducted within species, genera
and families as weil as for different regional floras (Lens et al. 2004). According to this
author the degree of adaptation to ecological gradients may differ considerably among
plant groups and macroclimate, and the impact of different life forms and the amount
of precipitation plays a significant role in various wood features.
According to Dickison and Phend (1985), wood characteristics of Styrax show sig-
nificant correlations with latitude, water availability and soil conditions. In a previous
study on Styrax camporum from the Brazilian cerrado, Machado et al. (1997) observed
scalariform perforation plates in the stern wood, and combined simple and foraminate
perforation plates in the root wood. The combined occurrence of simple and scalariform
plates in the stern wood has already been described in Styrax stern wood by different
authors and was suggested to be an adaptation to seasonally dry regions (Carlquist
1980; Baas etal. 1983; Dickison & Phend 1985).
With some exceptions (e.g. Gasson & Cutler 1990), root wood anatomy of plants
in general has received much less attention than stern wood anatomy. Physiological
and anatomical studies have demonstrated that within a species, root xylem has wider
vessels than stern xylem and that root wood is more vulnerable to emboli sm than stern
xylem (Alder et al. 1996; Ewers et al. 1997; Machado et al. 1997; Kavanagh et al.
1999; Kolb & Sperry 1999; McElrone et al. 2004; Psaras & Sofroniou 2004).
In addition to a previous study on S. camporum (Machado et al. 1997), the objective
of this study was to investigate variations in stern and root wood structures within and
among five species of Styrax that inhabit both the cerrado and the Atlantic forest.
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MATERIALS AND METHODS
Our sampling inc1udes five species of Styrax growing in different habitats. Styrax lati-
folium Pohl and S. martii Seub. were collected in upland semi-deciduous seasonal
forests and S. leprosus Nees et Mart. was collected in a riparian forest with seasonally
ftooded soil. These three species were all from remnants of the Atlantic forest. Sampies
of S. camporum Pohl and S.ferrugineus Nees et Mart. were from the cerrado. All these
habitats are situated in the municipality ofBotucatu (22° 55' S, 48° 30' W), Silo Paulo
state, south-eastem Brazil. The local average annual rainfall in all sites is about 1300
mm, with a mean annual temperature of 20°C and monthly mean temperature ranging
from 25°C in January to 15°C in July. July is the driest and coldest month and January
is the wettest and warmest month.
For each species we sampled sterns and the main root from adult specimens (three
replicates per species from the forest and one replicate per species from the cerrado)
(Table 1). We observed that the cerrado species have deep axial roots (approx. 12 m in
depth) and the forest species have shallow roots, horizontally spread. Root sampies were
collected at 30-50 cm distal from the root-stem junction. Careful sampling ensured
that all root sampies were collected from Styrax plants. Stern sampies were taken about
60 cm above the soil in the cerrado species and about 130 cm above the soil in the
forest species.
Table 1. Collection data for the five species of Styrax studied. - E = environment: F: semi-
deciduous seasonal forest, RF: riparian forest, C: cerrado. - H = habit: T: tall tree, S: small
tree, Sh: shrub.
Root Stern
Herbarium
number Wood- Mean Wood Mean Mean
Speeies E H (BOTU) eolleetion diameter* eolleetion height DBH**
number (ern) number (m) (ern)
S. latifolium F T 17833, BOTw 1372, 14 BOTw 1375, 10 20
17834, 1373,1374 1376,1377
17835
S. martii F S 17830, BOTw 1378, 7 BOTw 1381, 5 10
17831, 1379, 1380 1382, 1383
17832
S.leprosus RF S 17836, BOTw 1384, 3 BOTw 1387, 3 4
17837, 1385, 1386 1388, 1389
17838
S. camporum C Sh 17456 SPFw 302 2 SPFw 303 2 5
S. jerrugineus C S 17820 BOTw 1392 5 BOTw 1393 4 8
* Mean diameter: 30-50 em from the base.
** DBH: diameter at breast height (1.3 m).
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via free accessTable 2. Selected qualitative and quantitative root and stern wood characters in Styrax. - E =environment: F: semi-deciduous seasonal forest, Ict
RF: riparian forest, C: cerrado. - Vessels: /sq.mm = vessels per square millimeter; pp = perforation plates: S: simple, SC: scalariform, FR:
foramino-reticulate; IPd = intervessel pits diameter. - Fibres: pits: S: simple, B: bordered; S: septate: - (absent), + (present). - Rays: #/mm =
number of ray per millimeter; width (!-lm) = rays width in !-lm; height (!-lm) = height of non-fused rays in !-lm.
Vessels Fibres Rays
E diam. length /sq.mm pp IPd diam. length pits S #/mm width FR height
(!-lm) (!-lm) Ütm) (!-lm) (!-lm) (!-lm) (!-lm)
S. latifolium F
Root 69±1l 755±198 16±2 SC 6±1.0 31±4 1529±21O B + 24±2 23±7 + 385±149
Stern 91±14 970±197 19±4 SC 7±1.3 28±4 1904±317 B 23±2 17±3 542±158
S. martii F
Root 66±12 902±162 16±4 SC 6±1.0 30±6 1697±347 S 24±1 28±13 + 710±284
Stern 97±17 873±197 17±4 SC 5±1.2 22±4 1798±262 B 25±2 23±7 843±193
S.leprosus RF
Root 63±17 803±22 20±4 SC 4±0.7 26±4 1703±278 B + 21±2 23±7 + 644±322
Stern 69±17 853±157 27±7 SC 4±0.7 22±4 1811±294 B 28±1 15±7 + 690±342 I ......
~
>
S. camporum C
"-
0
Root 159±35 682±183 33±6 S/FR 5±1 26±3.8 1300±264 S + 8±1 58±24 - 788±320 =
Stern 72±14 738±121 58±15 SC/FR 4±1 21±2.8 1207±169 B 16±2 31±9 623±229
9
+ ~
S.ferrugineus C ~
N
00
Root 105±25 730 ± 170 21±7 SC/FR 6±0.8 27±5 1170±170 S/B 11±1 52±13 + 770±270
Stern 73±19 528±160 31±10 SC/FR 5±0.8 26±4 1100±140 SIB + 15±1 61±16 + 750±330 ;g
N
0
0
-.J
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The vouchers and sampIes of root and stern wood of each species are deposited,
respectively, in the Herbarium (BOTU) of the Botany Department and in the Wood
Collections: BOTw of the Natural Resources Department, Silo Paulo State University
and SPFw of the Botany Department, Silo Paulo University.
Mature wood sampIes were fixed in alcohol 70 %. Transverse, radial and tangential
sections (10-18 f..lm) were cut using a sliding microtome. These sections were double-
stained with 1% aqueous solution of fuchsin and astra blue (Roeser 1972) and mounted
permanently in Permount synthetic medium. Some root and stern material was mac-
erated in a mixture of equal volumes of acetic acid and hydrogen peroxide at 60°C
(Johansen 1940) for 12 to 24 hours. The material was stained with 1% aqueous solution
of safranin and mounted in glycerin. For the histochemical tests, freehand sections of
fresh material were treated with femc chloride for identification of phenolic compounds
(Jen sen 1962), and potassium iodide for starch grains (Johansen 1940). The presence of
calcium oxalate was confirmed, since dilutions with hydrochloric acid (HCl) produced
no effect (Chamberlain 1932).
Wood descriptions follow the IAWA Committee (1989). The wood colors follow
Munsell (1957). Quantitative data are based on 30 individual counts; the statistical re-
quirements for minimum numbers of measurements were fulfilled:
N = (t value)2. (sampie variance) 1 (accuracy of 10% x sampIe mean)2,
following Freese (1967) and Eckblad (1991). The numerical values given in Table 2
are the means accompanied by standard deviation. For the statistical analysis we used
Cluster Analysis and Principal Component Analysis (Sneath & Sokal 1973) to see if we
could provide quantitative support for the qualitative differences encountered between
forest and cerrado species.
RESULTS
The most important anatomical features of Styrax stern and root are summarized in
Table 2. A detailed wood anatomical description of the Styrax species folIows.
General description - Wood light brown (10YR-7/4) in the root of S.latijolium, S.
martii, S. leprosus and in the stern of S. camporum and S.jerrugineus, wood from light
brown (10YR-7/4) to light reddish (7/3) in the stern of S. martii, S.leprosus, wood from
light brown (10YR-7/4) to reddish brown (5YR-5/4) in the rootof S.jerrugineus and in
the stern of S. latijolium; wood texture fine in the stern of S. martii, S. camporum and
in the root and stern of S. jerrugineus; texture fine to medium in the root and stern of
S. latijolium, in the root of S. martii and in the stern of S. jerrugineus; texture medium
in S. camporum and S.jerrugineus; wood bright, regular in grain, smooth, and without
odor and taste in all species.
Growth increments - Delimited by tangential zones ofthick-walled flattened fibres
in the root wood of S. martii, S.jerrugineus and S. camporum and in the root and stern
wood of S. leprosus (Fig. 1-4) and S. latijolium. Absent in the other samples.
Wood anatomy - Vessels: mostly diffuse (Fig. 3,4), wood semi-ring porous in the
root wood of S. camporum and S.jerrugineus (Fig. 5); predominantly in multiples of
2-4 (Fig. 3-5) in all species (approx. 60% in the root and stern wood ofthe species
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Figures 1-4. Transverse seetions of Styrax leprosus wood showing growth incrernents. - 1: Root
wood. - 2: Stern wood. - 3 & 4: Thick-walled latewood fibres dernarcating growth incrernents
(arrows). - 3: Root wood. - 4: Stern wood. - Scale bars: 100 I-lrn in 1 & 2; 420 I-lrn in 3 & 4.
from cerrado: S. camporum and S. jerrugineus, and 80-95 % in the root and stern
wood of the species from forest: S. latifolium, S. martii and S. leprosus). The higher
vessel diameters are found in the stern wood from forest species and in the root wood
from cerrado species (Table 2). The vessel element length is variable, with higher
values in the stern wood when compared with the root wood, except in S. martii and
S.jerrugineus. The number of vessels per mm2 is quite variable in the species except
in S. latifolium and S. martii. Although scalariform perforation plates are found in the
wood of most species (Fig. 6-9), foramino-reticulate perforations are also occasionally
found in root and stern wood of S.jerrugineus (Fig. 10) and in S. camporum. Simple
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Figures 5-18. Root and stern wood of Styrax. - 5: Root wood transverse seetion of Styrax campo-
rum showing serni-ring porosity. - 6-9: Scalariform perforation plates in vessels. - 6: S. martii
stern. - 7: S.latifolium stern. - 8: S. martii root. - 9: S.latifolium root. - 10: Forarnino-reticulate
perforation plates in vessel of stern wood of S. jerrugineus. - 11: Simple perforation plate in
vessel of root wood of S. camporum. Note the seerningly vestured pits in the vesse) wall (arrow).
- 12: Alternate intervessel pits in S. latifolium stern. - 13: Pit charnber with pseudo-vestures
in S. martii. - 14: Vessel ray pits in S. martii stern. - 15: Septate fibres in S. leprosus stern. -
16: Cavity (arrow) in fibre ofroot wood of S.jerrugineus. - 17 & 18. Axial parenchyrna strands
and rnultiseriate and uniseriate rays in tangential seetion. - 17: Root wood of S. camporum. -
18: Stern wood of S.jerrugineus. - Scale bars: 500 !!rn in 5; 25 !!rn in 6; 50 !!rn in 7, 9, 10 &
15; 100!!rn in 8,16,17 & 18; lO!!rn in 11 & 14; 7!!rn in 12; 2!!rn in 13.
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perforation plates are found only in S. camporum root wood (Fig. 11). The number of
bars in scalariform perforations varies from 3 to 15. The highest bar numbers are from
the stern wood of S.jerrugineus and S. camporum. Rims with vestured pits are present
in the simple and multiple perforation plates in the S. camporum root wood and in the
S. jerrugineus stern wood, respectively. Intervessel pits alternate, circular to oval in
a11 species (Fig. 12, 13),3-7 !-lm in diameter, with smaller values in S. leprosus and
S. camporum root and stern wood. Vestured pits appear to be present in root wood of
a11 species (Fig. 11). In some cases, small dots attached to the pit chamber as in root
wood of S. martii (Fig. 13) are considered to be pseudo-vestures. Vessel-ray pits are
similar to intervessel pits in shape and in diameter (Fig. 14). Thin-wa11ed tyloses occur
in vessels of the root wood central region of S. camporum. Yellowish to brown gum de-
posits in some vessels of the root and stern wood of S. camporum and S.jerrugineus. -
Fibres: with distinctly bordered pits predorninant; fibres with indistinctly bordered pits
in combination with fibres with distinctly bordered pits in the root and stern wood of
S.jerrugineus, and libriform fibres only in the root wood of S. martii and S. camporum
(Table 2); thin- to thick-wa11ed, with high medium values in the root and stern wood
ofthe species from forest and in the stern wood of S.jerrugineus. Septate fibres in the
root wood of S. latifolium, S. leprosus and S. camporum (Fig. 15) and stern wood of
S.jerrugineus. Fibre cavities occur in the root wood of S.ferrugineus (Fig. 16). - Axial
parenchyma: diffuse-in-aggregates apotracheal and scanty paratracheal in a11 species
(Fig. 3,4); variable from 4-6 ce11s per strand in the root wood of S. camporum; 4-12
cells per strand in the stern wood of S. latifolium, S. camporum and S. jerrugineus;
6-13 cells per strand in the root wood of S. jerrugineus and root and stern wood of
S. martii and S.leprosus; and 10-17 cells per strand in the root wood of S.latifolium. -
Rays: predominantly multiseriate (Fig. 11, 18) variable from 80 to 92 % in a11 species;
heteroce11ular (Fig. 19, 20), with 4-23 marginal rows of upright and/or square ce11s
except for root wood of S. latifolium with square and upright cells intermixed, and
S. camporum with procumbent, square and upright ce11s intermixed. Perforated ray
ce11s: present in uniseriate rays and in the uniseriate portions of the multiseriate rays
(Fig. 21-23) in the root and stern wood of S.leprosus, S. camporum and S.jerrugineus
and in the root wood of S. latifolium and S. martii; isolated except in the root wood of
S. camporum in which they occur in groups of 2 or 3; with simple perforation plates
in the root wood of S. camporum (Fig. 21), with scalariform perforation plates in the
root and stern wood of other species (Fig. 22, 23); occasionally with some reticulate
perforation plates in the root and stern wood of S.jerrugineus; rectangular and larger
than adjacent cells; pits similar to intervessel pits. - Mineral inclusions: calcium
oxalate prismatic crystals in chambered axial parenchyma ce11s in a11 species (Fig. 24),
and in non-chambered and chambered square and upright ray cells in the root and
stern wood of S. camporum, and in the stern wood of S. martii. - Organic contents:
phenolic compounds in axial parenchyma of stern wood of S. leprosus and in ray cells
of root wood in S. camporum and S. leprosus.
Statistical analysis - The statistical analyses revealed two main findings in the root
features. First, the species from the forest can be distinguished from those ofthe cerrado
(Fig. 25, 26). Secondly, the species S.jerrugineus and S. camporum, both growing in
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Figures 19-24. Root and stern wood of Styrax. - 19. Stern wood. - 20. Root wood. - 19 & 20:
Radial sections of S. camporum showing heterocellular rays. - 21-23. Perforated ray cells. - 21:
Simple perforated ray cells in root wood of S. camporum. - 22: Scalariform perforated ray cells
in stern wood of S. camporum. - 23: Macerated wood of S. camporum stern wood showing two
vessel elements connected by a scalariform perforated ray cel!. - 24: Calcium oxalate prismatic
crystals in chambered axial parenchyma cells in the stern wood of S. martii. - ScaIe bars: 500
11m in 19 & 20; 50 11m in 21 & 24; 125 11m in 22; 100 11m in 23.
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0.36 0.32 0.28 0.24 0.20 0.16 0.12
I I I I I
S. latifolium
S. martii
S.leprosus
S. jerrugineus
L -_____________________________________ S.camporum
Figure 25. Dendrogram resulting from Cluster Analysis of eleven characteristics of root wood in-
cluding five Styrax species from the Atlantic forest and cerrado (see Table 3 for characteristics).
Y2
0.3
0.25
• S. jerrugineus
0.2
0.15
0.1
0.05
S.leprosus
0.6
YI
-0.3 -0.2 -0.1 0.1 0.2 0.3 0.4 0.5
-0.05
• • S.martii
•
S. latijolium S. camporum
-0.1
-0.15
Figure 26. Principal Component Analysis of root wood characteristics based on five species of
Styrax from the Atlantic forest and cerrado (see Table 3 for statistics).
0.36 0.32 0.28 0.24 0.20 0.16 0.12
I I I I I I I
S. latifolium
S. martii
S.leprosus
S. camporum
S. jerrugineus
Figure 27. Dendrogram resulting from Cluster Analysis of eleven characteristics of stern wood in-
cluding five Styrax species from the Atlantic forest and cerrado (see Table 3 for characteristics).
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Y2
0.25
• S.jerrugineus
0.2
0.15
0.1
•
S. latifolium
0.05
S. marlii.
0.3
Y1
-0.4 -0.3 -0.2 -0.1 0.1 0.2
-0.05
-0.1
• S. camporum -0.15
• S. leprosus
-0.2
Figure 28. Principal Component Analysis of stern wood characteristics based on live species of
Styrax from the Atlantic forest and cerrado (see Table 3 for statistics).
Table 3. Correlation between the eleven anatomical variables from root and stern of live
Styrax species and the main components (Y 1 and Y2). Percentage of restrained and accu-
mulated information in Y I and Y2 and ordination of variables (number between brackets)
conceming to their discrimination.
Quantitative characters Root Stern
Y1 Y2 Y1 Y2
Vessel elements
Diameter (flm) 0.9965 (1) -0.0194 (11) 0.7679 (6) 0.3589 (10)
Length (flm) -0.7402 (6) -0.0430 (10) 0.8540 (3) -0.4572 (4)
Number/sq.mm 0.9550 (2) -0.2168 (8) -0.8371 (4) -0.4530 (6)
Vulnerability index (v) 0.6576 (8) 0.4735 (2) 0.8987 (2) 0.3732 (8)
Intervessel pit diameter (flm) -0.1026 (11) 0.4649 (3) -0.5590 (8) 0.4532 (5)
Fibres
Diameter (flm) -0.6054 (10) -0.0880 (9) 0.2289 (9) 0.5957 (3)
Length (flm) -0.7372 (7) -0.5563 (I) 0.9582 (1) -0.2553 (11)
Rays
Number/mm -0.9363 (4) -0.2965 (7) 0.8270 (5) -0.3653 (9)
Width (flm) 0.9364 (3) 0.3470 (6) -0.7235 (7) 0.6867 (2)
Height (flm) 0.6377 (9) 0.3549 (5) 0.0349 (11) 0.4234 (7)
Height of fused rays (flm) -0.8988 (5) 0.4198 (4) -0.1967 (10) -0.7493 (1)
Restrained variance (%) 76.95 12.39 62.92 22.89
Accumulated information (%) 76.95 89.34 62.92 85.81
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cerrado, reveal mutual differences, with S.ferrugineus more similar to the forest spe-
cies than to S. camporum (Fig. 26). The root wood characteristics that contribute to the
separation of forest species from cerrado species are: vessel element diameter and length
and number of vessels per mm 2 ; length of fibres; width and density of rays (Table 3).
For the stern wood there is a c1ear split between the forest and the cerrado species
(Fig. 27, 28). The stern wood characteristics that contribute most to the separation of
forest species from cerrado species are: vessel element length and number of vessels
per mm2 ; length of fibres; width and density of rays (Table 3).
DISCUSSION
The structure of stern wood of the Styrax species studied agrees in general terms with
previous descriptions ofthe wood ofthe Styracaceae (Metcalfe & Chalk 1950; Dickison
& Phend 1985) and inc1udes vessels arranged in a diffuse-porous pattern, predominantly
vessel multiples, multiple perforation plates, intervessel pits arranged in an alternate
manner, fibres with indistinctly to distinctly bordered pits, axial parenchyma distrib-
uted as a combination of diffuse-in-aggregates and scanty paratracheal, multiseriate
heterocellular rays predominantly, and prismatic crystals in axial parenchyma cells.
This study demonstrates that the wood anatomy of Styrax species shows qualitative and
quantitative differences between species from theAtlantic forest and cerrado as weIl as
between root and stern wood from a single specimen in the same species.
The occurrence of growth rings in the root wood of all Styrax species studied disa-
grees with Lebedenko (1962), who suggested that root wood is less probable to form
growth rings because ofthe uniformity ofthe environmental conditions ofthe soil. The
seasonal soil water availability in the cerrado and forest may be an important factor
affecting the formation of growth rings in these species.
Styrax camporum and S.jerrugineus, wh ich inhabit the cerrado, show a larger vessel
diameter in the root wood than in the stern wood. The presence of these larger vessels
could be related to higher water potentials in this organ, which drops along a gradient
from root via stern to leaf (Zimmermann 1983). Roots would therefore be less exposed
to dangers of drought-induced embolism (air blockage). According to Ewers et al. (1992,
1997), embolisms may be more readily reversible in roots than in sterns, in part because
positive root pressures, which could dissolve embolisms, are dissipated with height up
the stern (Sperry et al. 1987; Tyree & Yang 1992; Yang & Tyree 1992; Cochard et al.
1994; Ewers et al. 1997; Fisher et al. 1997). Although there is no experimental evidence
of root pressure in Styrax species, we agree with Ewers et al. (1997) who suggest that
wider vessels in roots, if embolized, may have a better chance of being refilled than
embolized vessels of similar diameter within sterns. Although S. camporum and S.ferru-
gineus occur in the cerrado where the soil is compact and dry for the first few metres
of depth, the water availability increases at greater depths (Ferri 1979) and their roots
are extensive enough to reach the water table (Machado 1991). In contrast, the roots
of forest species are shallow and therefore more subject to variations in water avail-
ability. The narrower vessels in the root wood could be a way of providing safety
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via free accessMachado et al. - Root and stemwood of Styrax 185
against cavitation when the water availability is minimal (Carlquist 1966; Carlquist &
Hoekman 1985; Carlquist 1988).
Styrax camporum and S.jerrugineus show semi-ring porosity patterns in their root
woods. Carlquist (1988) considered semi-ring porosity patterns as an ideal balance
between satisfying peak transpirational demand when water availability is high during
the wet season as the wide vessels would accommodate greater volumes of water per
unit time in earlywood than in latewood. Also, the narrow vessels in the latewood of
semi-ring porous species meet requirements for safety from cavitation during the dry
season. Ellmore and Ewers (1985) hypothesize increased safety in latewood if narrower
vessels embolize less readily than wider ones.
Scalariform perforation plates were found in the wood of most species of Styrax
studied, except in S. camporum root wood. Based on previous studies (all on stern wood),
multiple perforation plates are characteristic of the Styracaceae, and simple plates are
considered an exception. Simple and scalariform plates in combination were observed
in the stern wood of S. platanifolius and S. texanus, species with distinctiy ring-porous
or semi-ring-porous wood, which inhabit seasonally dry habitats of the southwestern
United States (Dickison & Phend 1985). In these species, simple perforation plates are
restricted to the wider earlywood vessels while narrower latewood vessels possess only
scalariform perforations. The combined occurrence of simple and multiple perforations
in the root wood of S. camporum that inhabit cerrado, a seasonal dry environment, may
be correlated to the serni-ring porosity pattern as reported by Dickison and Phend (1985).
Although the combination of scalariform and simple plates in some Styrax species have
been considered an adaptation to seasonal drought by Dickison and Phend (1985), recent
studies suggest that the gains in hydraulic conductivity from simple perforation plates
would be small (Schulte & Castle 1993; Ellerby & Ennos 1998).
Cavities were observed in fibre walls in the root wood of S. jerrugineus. Cavities
have already been observed in tracheids, fibres, and axial parenchyma in different
dicotyledon families (Gomes et al. 1988; Luchi & Mazzoni-Viveiros 1988; Zhong
et al. 1992; Dias-Lerne & Angyalossy-Alfonso 1998; Luchi 2003). The possible func-
ti on of these cavities in wood cells could not be determined.
The predominance of the fibres with distinctly bordered pits in the wood of Styrax
species studied agrees with previous descriptions ofthe wood of Styracaceae (Carlquist
1988). Septate fibres, comrnonly observed in the root wood of Styrax species studied,
are most likely a new feature in the wood of Styracaceae. These living fibres may
represent a means of water and starch storage, as weil as an alternative photosynthate
storage in taxa where growth and fiowering events are constant (Carlquist 1988).
Perforated ray cells in Styracaceae were described for the first time in S. camporum
(Machado & Angyalossy-Alfonso 1995). Although perforated ray cells were observed
in all species studied, their functional role remains unclear.
The most informative quantitative features in the root wood that differentiate forest
species from cerrado species were diameter, length of vessel elements and frequency of
vessels, length of fibres, width and frequency of rays. In the stern wood, length and fre-
quency of vessels, length of fibres, width and frequency of rays were the most informa-
tive features.
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via free access186 IAWA Journal, Vol. 28 (2), 2007
Some stern wood anatomical characteristics of S. camporum, such as small vessel
diameters, high vessel densities and short vessel elements, can partly be explained by
its shrubby habit, as observed by Lens et al. (2004) for Ericaceae.
The variation between Styrax root and stern wood may be the result of functional
adaptations especially in respect to conductive efficiency and safety. Since the Styrax
species studied are subject to the same c1imatic conditions, the impact of habit, tree
size (height and diameter), and soil type may partly explain the correlation values
observed.
ACKNOWLEDGEMENTS
The authars are grateful to Conselho Nacional de Desenvolvimento Cientffico e Tecnol6gico (CNPq -
Proc. 30241/2002-0) and Funda~äo de Amparo a Pesquisa do Estado de Säo Paulo (FAPESP: Proc.
92/1915-4 and BIOTA Program - Proc. 00/12469-3) far the financial support.
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