BARK AND WOOD ANATOMY OF - UNCARIA GUIANENSIS AND UNCARIA TOMENTOSA - Brill
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IAWA Journal, Vol. 26 (2), 2005: 239 – 251
BARK AND WOOD ANATOMY OF
UNCARIA GUIANENSIS AND UNCARIA TOMENTOSA
(“Catʼs claw”)
Helga Lindorf
Centro de Botánica Tropical, Instituto de Biología Experimental, Facultad de Ciencias,
Universidad Central de Venezuela, Apartado 47114, Caracas 1041A, Venezuela
SUMMARY
Uncaria guianensis (Aubl.) J.F. Gmel. and Uncaria tomentosa (Willd. ex
Roem. & Schult.) DC. (Rubiaceae) have a bark commonly used medici-
nally by ethnic peoples in South America. Both plants, which are called
“catʼs claw”, are now being commercialised, but unfortunately they are
often sold adulterated with other species. The aim of this work was to
determine anatomical features of diagnostic value that could allow the
recognition of the bark of both species as raw or processed products. The
wood anatomy was also studied. The bark of these two species of Uncaria
is very similar, but they differ in the distribution of fibers and the presence
of styloids. The wood of both taxa is homogeneous and there are only
slight differences in quantitative aspects of conducting elements.
Key words: Uncaria guianensis, Uncaria tomentosa, catʼs claw, Ru-
biaceae, bark, wood, folk medicine.
INTRODUCTION
Uncaria guianensis (Aubl.) J.F. Gmel. and U. tomentosa (Willd. ex Roem. & Schult.)
DC. are two climbing species of Rubiaceae found in the Caribbean, and in Central and
South America (Steyermark 1974; Ridsdale 1978). They are known by the common
name of “uña de gato” (catʼs claw) in most countries where they grow because the
vegetative branches have the shape of hooks (in Venezuela, U. guianensis is known as
“uña de gavilán” (falconʼs claw) in certain regions). The morphology of these hooks was
used by Steyermark (1974) as a differentiating character, noting that in U. guianensis
they are markedly curved and glabrous from the young stages, whereas in U. tomentosa
they are only slightly curved, tomentellous to glabrous. Besides these two Neotropic
taxa, the genus Uncaria includes paleotropical species. According to Ridsdale (1978),
29 species are found throughout Asia, Micronesia, Australia and Macaronesia, and three
in Africa and Madagascar. Andersson and Taylor (1994) note approximately 60 species
of Uncaria world-wide. All species of Uncaria are woody lianas with differing alkaloid
content, many with medicinal properties (Phillipson et al. 1978). The genus Uncaria
was first included into the Naucleeae tribe by Schumann (1891), later it was transferred
to the Cinchoneae tribe by Bremekamp (1966). Ridsdale (1978) ratified its position
among the Cinchoneae, comprising the subtribe Mitragynineae along with the genus
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Mitragyna. Afterwards, it was placed among the Coptosapelteae tribe by Andersson
and Persson (1991). Recent morphological and molecular evidence (Razafimandim-
bison & Bremer 2002) suggest that the demarcation limits of the Coptosapelteae tribe
sensu Andersson is no longer sustainable and that its members (including Uncaria)
should be grouped within the Naucleeae s.l., therefore adding weight to Schumannʼs
original criteria.
Uncaria guianensis and U. tomentosa long have been used in traditional medicine
among various Latin-American native peoples, particularly for tumours, inflammations,
degenerative and immunological diseases, and birth-control. The part most commonly
employed in traditional medicine is the bark, although the leaves also are used (Uphof
1968; Phillipson et al. 1978; Gupta 1995). The World Health Organisation recognised
U. tomentosa as a medicinal plant in 1994 and authorised its world commercialisation.
Its bark is sold commercially in chunks, milled or ground; in the pharmaceutical indus-
try it is processed into capsules, tablets and ointments (Buitrón 1999). The potential
curative properties of the neotropical species of Uncaria justified the holding of the 1st
International Conference on these taxa in August 2001 in Iquitos, Peru. At that meeting
results of botanical, chemical, agro-technological, pharmacological, toxicological and
clinical studies on these two plants were presented .
In Metcalfe and Chalkʼs classic volumes (1950) there are only few references to the
histological characteristics of the genus. Lindorf (2000, 2001; Roth & Lindorf 2002)
presented results on selected aspects of the bark anatomy of these two species. The
wood anatomy of Uncaria guianensis (Aubl.) Gmel. and U. africana G. Don was studied
by Koek-Noorman (1969a, b, 1970), and wood of U. africana G. Don var. xerophila
E.M.A. Petit and U. donisii E.M.A. Petit was studied by Jansen et al. (2002).
Often in the commercialisation of the bark, U. tomentosa is confused and adulter-
ated with U. guianensis as well as with Mimosa species that are also called catʼs claw
(Buitrón 1999). Uncaria guianensis bark is less used commercially. Its alkaloid content
differs from U. tomentosa (Phillipson et al. 1978; Lock de Ugaz 1994); it is less effec-
tive medicinally because it lacks certain components that are present in U. tomentosa
(Steinberg 1994).
Because both species are called catʼs claw and can coexist in the same environment
it would be useful to determine if there are anatomical characteristics that characterise
each species, so as to enable the microscopic identification of the bark as raw or proc-
essed products. With this objective in mind, the present study on the bark and wood
anatomy of Uncaria guianensis and U. tomentosa was undertaken.
MATERIALS AND METHODS
Table 1a lists the samples studied. The fresh samples of U. guianensis came from a
cultivated specimen in the Orinoco Botanical Garden and those of U. tomentosa were
collected in the Caparo Forest Reserve in the great plains or llanos. Additionally, com-
mercial samples of dried and milled or pulverised bark, and pharmaceutical capsules
were also analysed particularly for determination of the presence of styloids (Table
1b).
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Table 1a. Samples examined.
Species Collectorʼs number. Herbarium Nr. Styloids
Uncaria guianensis F. Guánchez 2178 VEN 235139 +
R. Liesner & A. González 11396 VEN 161991 +
Morillo, Rutkis & Panapera 9196 VEN 172414 –*
L. Rodríguez 59 In preparation +
Rosales, Briceño, Guevara & Pino 274 MYF13053 +
F. Matos 698 MER 014858 +
F. Delascio & F. Guánchez 10895 MER 040678 +
L. Aristeguieta n/n Fresh sample +
Uncaria tomentosa Steyermark, Bunting & Blanco 101982 VEN 78083 –
E. & S. Zent n/n MYF 16307 –
O. Huber & H. Canales n/n MYF 2167 –
C. Hernández 1104 MER 047937 –
J. Guevara 2435 In preparation –
L. Aristeguieta n/n Fresh sample –
* In this specimen parenchyma cells have brown contents or are completely filled with starch
grains.
Table 1b. Products examined.
Form of presentation Brand Styloids
Dried bark (Uncaria tomentosa) Los Ficus, Peru –
Dried bark (U. tomentosa) Monard, Peru –
Dried bark (U. tomentosa) Mi Naturaleza Amazónica, Peru –
Capsules (U. tomentosa) Nulab Inc.,USA –
Capsules (U. tomentosa) Laboratorio Angisa, Peru –
Tea (catʼs claw) Harnimans, Peru +
Powder (U. tomentosa) Mi Naturaleza Amazónica, Peru –
Samples were softened in a mixture of alcohol 70% and glycerine. After several
days in the softening solution, transverse, radial and tangential sections were cut with
a sliding microtome. The sections were stained with toluidine blue and mounted in
Euparal. Macerated bark and wood tissue was prepared according to Franklin (1946)
with a 1:1 mixture of acetic acid and hydrogen peroxide, and mounted in semipermanent
form on diluted glycerine using safranin as a colouring agent and nail varnish to seal
the edges. The milled bark as well as the powder extracted from the pharmaceutical
capsules were carefully spread over the glycerine on the slides, which were also sealed
with nail varnish. Quantitative data are based on 25 measurements as per recommenda-
tions of an IAWA Committee (1989). The terminology used for the bark follows Roth
(1981), Trockenbrodt (1990), and Lev-Yadun (1991).
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1 2
3 4
Fig. 1–4. Bark anatomy of neotropical Uncaria species. – 1: Cross section of U. tomentosa showing
rhytidome with three periderms. – 2: Detail of the periderm. See phelloderm with phellosclereids. –
3: Dilatation growth in cross section of U. guianensis. Parenchymatic cells in the phloem and in the
periphery of some rays extend tangentially and divide (arrow). – 4: Tangential section of U. guian-
ensis showing dilatation growth in the rays. Note dark colour in some cells probably due to phenolic
contents. Rays are flanked by fibres. — Scale bars: 1, 3, 4 = 100 μm; 2 = 30 μm.
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5 6
7 8
Fig. 5 & 6. Details of the secondary phloem of Uncaria guianensis. – 5: Tangential section showing
scalariform sieve plates. Styloids are visible in some parenchyma cells (arrowhead). – 6: Radial
section showing two sieve plates. Several lateral sieve areas are observed to the left-hand side of
the picture. — Fig. 7 & 8. Stratification of fibres and phloem in cross section. – 7: U. tomentosa.
Note fibre bands with sieve tubes. – 8. U. guianensis. Fibre bands are narrower than those in U.
tomentosa, and have no sieve tubes. — Scale bars: 5 = 50 μm; 6 = 20 μm; 7, 8 = 100 μm.
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9
10
11
13 12
Fig. 9 & 10. Styloids of Uncaria guianensis. – 9: Fibre bundles of bark, in cross section, show-
ing a styloid in a ray cell (arrow). – 10: Styloid observed with polarised light. — Fig. 11 & 12.
Diagnostic features observed in the powder contained in pharmaceutical capsules of U. to-
mentosa. – 11: Crystal sand (arrow) and compound starch grains (arrowhead). – 12: Group of
fibres crossed by ray cells filled with crystal sand. — 13. Tangential section from a fresh sample
of stem of U. tomentosa. Compare with Fig. 12. — Scale bars: 9, 11 = 30 μm; 10 = 10 μm;
12, 13 = 100 μm.
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14 15
Fig. 14 & 15. Macerated bark of Uncaria guianensis showing fibres and ray cells filled with crys-
tal sand and styloids. – Scale bars: 14 = 100 μm; 15 = 50 μm.
RESULTS
General characteristics of the bark (Fig. 1–15; Table 2)
Scaly rhytidome consisting of 2–4 periderms and the collapsed tissue between them.
Sequential periderms, slightly curved, formed as discontinuous layers connected to the
older layers. Sometimes only one periderm occurs. Phellem formed by 6–10 rows of
cells with walls uniformly thickened. Phelloderm composed of 2–7 rows of sclerotised
cells with walls evenly thickened, showing appearance of stone cells (phellosclereids,
according to Lev-Yadun 1991). Sieve tubes solitary or in small groups; sieve plates
inclined, compound, scalariform, with 6–11 sieve areas; lateral sieve areas present.
Fibres in rectangular bundles 2–11 cells high and 1–6 cells wide forming tangential
bands alternating with the phloem tissue. Axial parenchyma strands of 5–10 cells; cells
sometimes tangentially dilated, divided and transformed into sclereids. Rays uniseriate
and multiseriate, partially dilated towards the periphery due to the tangential extension
of the cells and their subsequent division. Uniseriates composed of upright or square,
sometimes globose cells. Multiseriates heterocellular, with 4–9 marginal rows of upright
cells and procumbent cells in the body; cells mostly globose, sometimes transformed
into sclereids. Rays occasionally deviated and obliterated in the phloem region. Organic
brown contents, presumably phenolic, present in scattered cells with thickened walls
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Table 2. Quantitative bark features of Uncaria guianensis and U. tomentosa.
Uncaria guianensis Uncaria tomentosa
Sieve element diameter (μm) 32 33
(22–45) (21– 53)
Sieve element length (μm) 374 644
(176–627) (402 – 951)
Fibre bundle height (μm) 121 163
(68–167) (53 – 333)
Fibre length (μm) 1295 1257
(814–1647) (796 –1813)
Uniseriate ray width (μm) 31 24
(19–42) (14 – 45)
Uniseriate ray height (μm) 885 485
(426–1943) (144 – 984)
Multiseriate ray width (μm) 74 69
(47–103) (42 –136)
Multiseriate ray height (μm) 862 687
(537–1665) (341–1443)
Number of rays per mm 12 24
(9–16) (9 –17)
and truncated ends. Crystal sand abundant in cells of axial and ray parenchyma (in
U. guianensis styloids also present). Simple and compound starch grains very frequent;
the compound ones with 2, 3, and occasionally more components.
General characteristics of the wood (Fig. 16–21; Table 3)
Wood diffuse-porous. Growth rings absent. Vessels mostly solitary or in radial mul-
tiples of 2–4, with circular outline. Vessel elements with short or long tails. Perforation
plates simple. Intervessel pits vestured, alternate, bordered, circular to elongate, small
(4.5 μm). Vessel-ray pits similar to intervessel pits in size and shape. Vascular tracheids
intergrading with narrow vessel elements. Ground tissue composed predominantly of
thin- to thick-walled fibres with bordered pits (fibre-tracheids); non-septate fibres with
simple to minutely bordered pits (libriform fibres) also present. Axial parenchyma pre-
dominantly diffuse apotracheal, 6–11 cells per parenchyma strand. Scanty paratracheal
parenchyma also present. Rays uniseriate and multiseriate; frequently two or more rays
joined vertically. Uniseriates composed of upright or square, sometimes globose cells.
Multiseriates 2–4 cells wide. Rays Kribs heterogeneous I with 4–11 marginal rows of
upright cells and procumbent cells in the body, occasionally the multiseriate portion
of the rays appear fragmented in several groups constituted predominantly of upright
or globose cells. Fat drops common in cells of the axial and ray parenchyma. Crystal
sand in cells of axial and ray parenchyma (in U. guianensis styloids also present).
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16 17
18 19
Fig. 16 & 17. Wood anatomy of Uncaria neotropical species. – 16: U. tomentosa showing solitary
and multiple vessels. – 17. U. guianensis with predominance of solitary vessels. — Fig. 18 & 19.
Macerated wood tissue. – 18: Group of tracheids of U. tomentosa. – 19: Uncaria guianensis. —
Scale bars: 16, 17 = 20 μm; 18, 19 = 50 μm.
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20 21
Fig. 20 & 21. Wood anatomy of Uncaria neotropical species. – 20: Radial section of U. guian-
ensis. – 21: Tangential section of U. tomentosa. — Scale bars: 20, 21 = 100 μm.
Table 3. Quantitative wood features of Uncaria guianensis and U. tomentosa.
Uncaria guianensis Uncaria tomentosa
Vessels per sq.mm 28 33
(23 – 33) (24 – 38)
Solitary vessels proportion 83% 61%
Number of vessels per group 1.2 1.5
(1–2) (1– 4)
Tangential vessel diameter (μm) 131 166
(68 –212) (45 – 257)
Vessel element length (μm) 782 651
(592 –1092) (407–796)
Fibre length (μm) 1228 876
(759 –1628) (666 –1073)
Uniseriate ray width (μm) 25 23
(15 – 36) (15 – 30)
Uniseriate ray height 417 806
(174 –749) (188 –2258)
Multiseriate ray width 54 67
(36 – 83) (45 –106)
Multiseriate ray height 460 641
(318 – 49) (356 –1287)
Number of rays per mm 11 15
(9 –14) (12 – 20)
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DISCUSSION
The bark of Uncaria guianensis and U. tomentosa shows the following distinctive fea-
tures: a rhytidome with 2–4 periderms, with phelloderm composed of sclereids (some-
times only one periderm is observed); parenchymatic cells showing evident dilatation
growth; alternating bands of phloem and fibres; solitary fibres irregularly dispersed in
the parenchyma; crystal sand abundant in axial and ray parenchyma; a brown, possibly
phenolic content in many cells; simple and compound starch grains.
Dilatation growth is principally localised in scattered parenchyma cells, tangentially
extended and then divided (Fig. 3), that are often sclerotised later on, turning into scle-
reids. The vascular rays that reach the periphery are occasionally dilated tangentially
and may be also associated with the secondary formation of stone cells (Fig. 4).
The fibre bands are in rectangular groups or bundles separated by vascular rays,
whose cells are completely filled with crystal sand. The crossing of the fibres with the
rays and their cells, inflated and full of crystal sand, produce a characteristic picture in
longitudinal sections or macerated tissue and also in the powder contained in the phar-
maceutical capsules (Fig. 12 & 13). In the phloematic bands sieve tubes can be observed,
both dispersed or in groups in a radial pattern, 5–7 per row, sometimes disrupting the
fibre bundles.
In her studies on the anatomical structure of the bark of tropical trees, Roth (1981)
recognised fibre arrangement as the diagnostic criterion of greatest value, especially
as viewed in cross section and useful even in the field as seen with hand magnifiers.
Roth noted fibre bands in other Rubiaceae species, but reported dilatation growth and
the secondary formation of stone cells as being very scarce or missing in the family.
Consequently, the fibre and phloem stratification, jointly with dilatation growth and
secondary sclerosis, observed in the bark of the South American species of Uncaria,
are important characteristics for distinguishing them from other Rubiaceae.
Even though the bark of the two species of Uncaria studied is very similar, there are
some differences. The appearance of the fibre bands varies slightly in the two species
(Fig. 7 & 8; Table 2). In U. guianensis the fibre bands are irregular and occasionally wavy
and the distances between the bands, in radial direction, are occasionally very large. In
U. tomentosa fibre bands are conspicuously wavy and may almost touch neighbouring
bands and become concentric; they are more numerous and closer together, as seen in a
radial direction. The bundles or groups of fibres which constitute the bands are longer
(up to 11 fibres in a radial row) and more regularly and densely arranged in U. tomen-
tosa than in U. guianensis (2–4 fibres in a radial row). In U. tomentosa the groups
of fibres are normally penetrated by conductive elements. In U. guianensis the sieve
tubes generally remain separated from the fibre bundles, although they can occasion-
ally interrupt them.
In all but one of the examined samples of U. guianensis there were styloids and crys-
tal sand in the axial and ray parenchyma (Table 1a; Fig. 5, 9, 14, 15), while in U. to-
mentosa only crystal sand occurs (Table 1a; Fig. 12 & 13). These styloids have forked
ends (Fig. 10). They were also observed in a tea powder called catʼs claw. In commercial
samples of dried and pulverised bark labeled as U. tomentosa and in pharmaceutical
capsules labeled U. tomentosa they were absent (Table 1b). In the powder, characteristic
simple and compound starch grains and crystal sand were also detected (Fig. 11).
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Lindorf (2000, 2001; Roth & Lindorf 2002) reported that styloids generally were
absent from U. tomentosa, but generally were present in U. guianensis. The usefulness
of crystals for diagnostic purposes is known in various plants, but the formation of crys-
tals depends on fluctuations of the environment and their frequency and morphology
may also change during plant development. Therefore, to verify the diagnostic signifi-
cance of the styloids for distinguishing U. guianensis and U. tomentosa, it is necessary
to study a larger quantity of samples covering different microclimates.
Koek-Noorman (1977) defined two types of Rubiaceae wood. The first type is de-
scribed as having fibre-tracheids, parenchyma predominantly apotracheal, vessels soli-
tary or in short multiples and narrow rays with long uniseriate margins. A second type
is characterised by libriform fibres, absence of parenchyma or predominance of scanty
paratracheal parenchyma, vessels in long multiples and wide rays with few rows of
upright or square cells. This study found that Uncaria guianensis and U. tomentosa
are closest to the first type of wood. However, they also have scanty paratracheal
parenchyma as well as apotracheal and there are some fibres with simple to minutely
bordered pits. Uncaria africana G. Don. var. xerophila E.M.A. Petit, and U. donisii
E.M.A. Petit, also have the first type (Koek-Noorman 1970; Jansen et al. 2002). These
results suggest that Uncaria has homogeneous wood anatomy.
A close similarity was observed in the wood of the two species studied, limiting the
discrepancies to quantitative aspects, with reference to the number of vessels and their
grouping, and to the proportion of tracheids (Fig. 16–19; Table 3). Vessels are more
abundant in U. tomentosa. In U. guianensis the proportion of solitary vessels is higher
than in U. tomentosa. Though not quantified, a greater proportion of vascular tracheids
was observed in U. tomentosa. This greater density of vessels in U. tomentosa, as well
as the abundance of multiples and tracheids could be related to its tendency to occupy
a supra-canopy position, reaching the crowns of trees 20 to 30 m tall. Uncaria guian-
ensis is considered a scandent shrub which tends to occupy an intra-canopy position
(Bernal & Correa 1998; Andersson & Taylor 1994). A similar relationship between lian-
escent habit and the above mentioned features was found by Carlquist (1985) for other
species.
ACKNOWLEDGEMENTS
This study was supported by funds from the Consejo de Desarrollo Científico y Humanístico de la
Universidad Central de Venezuela (CDCH) for the projects N° 03.267.97 and 03.343.99. Botanical
colleagues Leandro Aristeguieta, José Guevara, Leyda Rodríguez and Stephen Tillett kindly provided
samples of material. Thanks are also due to Luis Hermoso, Alexandría Jiménez, Omaira Hockche and
Silvia Pérez-Cortez for their technical assistance.
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