Species Verification of Dalbergia 

nigra and Dalbergia spruceana

Samples in the Wood Collection 

at the Forest Products Laboratory

Michael C. Wiemann

Edgard O. Espinoza

United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

Research Paper

FPL–RP–690

March

2017
Abstract

To evade endangered timber species laws, unscrupulous

importers sometimes attempt to pass protected Dalbergia

nigra as look-alike, but unprotected, Dalbergia spruceana.

Wood density and fluorescence properties are sometimes 

used to identify the species. Although these properties are

useful and do not require special equipment, they may be

less reliable than direct analysis in real time–time of flight

mass spectrometry (DART–TOFMS). DART–TOFMS was

used to check identities of the D. nigra and D. spruceana

samples contained in the wood collection of the Forest

Products Laboratory (Madison, Wisconsin). Based on

DART-TOFMS, voucher-backed heartwood samples of the

two species are all correctly named, but some of the

unvouchered samples are not.

Keywords: Dalbergia nigra, Dalbergia spruceana,

caviunin, CITES, dalnigrin, DART-TOFMS, density, mass

spectrometry, principal components analysis, wood

anatomy, wood identification

March 2017

Wiemann, Michael C.; Espinoza, Edgard O. 2017. Species verification of 

Dalbergia nigra and Dalbergia spruceana samples in the wood collection 

of the Forest Products Laboratory. Research Paper FPL–RP–690. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products 

Laboratory. 10 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726-2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin.

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

Acknowledgments

Steve Verrill and Samuel Glass of the Forest Products

Laboratory and Peter Gasson of Kew Botanic Gardens gave

critical reviews that greatly improved the manuscript.

Geoffrey Kite of Kew Botanic Gardens and Thomas

Eberhardt of the Forest Products Laboratory also

commented and suggested corrections and improvements.

Barbara Hogan’s careful editing improved the readability of 

the paper. The cover shows Regis Miller examining samples 

in the Madison wood collection (upper photo) and Victor 

Deklerck holding a wood sliver at the mass spectrometer 

(lower photo).

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Introduction

Institutional wood collections are the primary sources of

research material for wood anatomy. They are essential to

validate the numerous wood identifications requested by

scientists, industry, and the public. The wood collection of

the USDA Forest Service, Forest Products Laboratory (FPL)

in Madison, Wisconsin, maintained by the Center for Wood

Anatomy Research (CWAR), was started in 1910 with the

opening of FPL (Miller 1999) and the hiring of the first

female scientist in the Forest Service, Eloise Gerry (Wayne

2011). The collection grew slowly; most of the original

samples were woods of the United States that were discards

from expositions and fairs (McBeath 1978). Samples were

gradually added, and in the 1940s, when it contained some

11,000 samples, newly hired curator B.F. Kukachka

reorganized the collection into a system in which samples

were arranged by family, genus, and species instead of by

accession number. This reorganization facilitated the

comparison of multiple samples of a taxon, but in the

process Kukachka discarded several thousand samples that

lacked voucher documentation (Miller 1999). Only two

samples of D. nigra (Vell.) Allem. ex Benth. (MAD7017 

and MAD10769; Table 1), both vouchered, survived the

purge. Additional samples of D. nigra (some vouchered,

some not) were subsequently added to the Madison 

collection (Table 1).

Accurate identification of D. nigra wood is especially

important because commercial trade of the species without

special permits is prohibited by the Convention on

International Trade in Endangered Species (CITES)

(Environment Canada 2002). Ensuring accurate

identification requires knowledge of the range of variability

that can be found in the species; this requires many samples

for comparison.

The supply of D. nigra samples at FPL was replenished by

the transfer of Yale University’s Samuel J. Record

collection (55,000 wood samples) in 1969 (Stern 1973;

Miller 1999) and the Chicago Field Museum collection

(20,000 wood samples) in 1971 (Williams 1971; Miller

1999). Some of the transferred samples were

voucher-backed although most were not, and some were

duplicates of samples already in the collection in Madison.

The samples from the Field Museum were integrated into

the Madison collection (MAD), although the herbarium

vouchers remained at the Field Museum (Williams 1971).

The wood collection from Yale (SJR) has been kept

separate, and its herbarium vouchers were transferred to

Madison; they are now in the herbarium of the University of

Wisconsin (WIS), kept as a separate collection. Information

pertaining to the SJR wood samples is kept in card

catalogues in the CWAR, and information pertaining to the

MAD wood samples can be found online (FPL 2017). The

CWAR now has about 30 samples of D. nigra, which is

fortunate because species protected by CITES (CITES 

2016), such as D. nigra, would be difficult to replace. For

unvouchered samples to be useful, however, their identity

must be verified.

Gasson and others (2010) compared the anatomy of

D. nigra with other species of the genus Dalbergia with

which it might be confused. For the Brazilian species, they

concluded that it could be distinguished from D. decipularis

Rizzini & Matt. based on color, from D. cearensis Ducke

based on vessel frequency, and from D. miscolobium Benth.

based on ray frequency. However, no anatomical characters

could consistently separate D. nigra from D. spruceana

Benth.

Separation of D. nigra from D. spruceana based on physical

properties was the subject of a report by Miller and

Wiemann (2006), and separation based on physical

properties and mass spectrometry is the subject of this one.

Miller and Wiemann (2006) used samples from the FPL

collection to find physical characteristics that could be used

to distinguish D. nigra from the look-alike species

D. spruceana, which has no CITES restrictions. The

physical properties used to separate the two species were

Species Verification of Dalbergia nigra and

Dalbergia spruceana Samples in the Wood

Collection of the Forest Products

Laboratory

Michael C. Wiemann, Botanist

Forest Products Laboratory, Madison, Wisconsin

Edgard O. Espinoza, Deputy Director

National Fish and Wildlife Forensic Laboratory, Ashland, Oregon
Research Paper FPL–RP–690

2

Table 1—Dalbergia nigra and Dalbergia spruceana samples in the Forest Products Laboratory wood collectiona

Collection No. Species label Location notes Voucher Sample notes

MAD 7017 D. nigra Bahia WIS Collected by H.M. Curran, 6; botanical 

material identified by Dr. Blake; 

=SJR4146

MAD 10769 D. nigra — WIS Collected by H.N. Whitford, 76; received 

from Smithsonian Institute, 3/6/1928; 

=SJR3273

MAD 13091 D. nigra Espirito Santo unknown Brazilian Forest Service 6; Nov. 1949

MAD 18588 D. spruceana Rio Juruá, 

Amazonas

NY Collected by B.A. Krukoff, 4921, 1933; 

Fourth expedition to Brazil, received 

from Syracuse

MAD 21010 D. nigra Brazil — From Fred C. Ness, National Rifle 

Association of America, Washington, 

DC, June 24, 1935; received from Field 

Museum in 1971

MAD 23334 D. nigra Brazil — Gift Set 57 from Instituto Florestal de Sao 

Paulo; received from Field Museum in 

1971

MAD 31954 D. nigra Brazil — Colombian Exposition, 1893; received 

from Field Museum in 1971, #01050

MAD 31955 D. nigra Brazil — Colombian Exposition, 1893; received 

from Field Museum in 1971, #01132

MAD 31956 D. nigra Brazil — Colombian Exposition, 1893; received 

from Field Museum in 1971, #01133

MAD 31957 D. nigra Brazil — Collected by Hildebrand, 17; received 

from Field Museum in 1971, #621818

MAD 31958 D. nigra Rio de Janeiro F, RB Collector unknown, 19; received from 

Field Museum in 1971, #622879

MAD 31968 D. spruceana Brazil WIS Collected by A. Ducke, 150; received 

from Field Museum in 1971, #614338; 

=SJR22610

SJR 550 D. nigra — — Veneer

SJR 1430 D. spruceana Lower Amazon — Brewer collection, 192; identified by S.J. 

Record

SJR 1442 D. nigra Lower Amazon — Brewer collection, 231; identified by S.J. 

Record, April 26, 1941

SJR 3107 D. nigra — — Donated August 1918 by Mr. Hargreaves 

of Alves Vasconcellos & Co., Rio de 

Janeiro, to H.N. Whitford; identified by 

S.J. Record, Oct. 1940

SJR 3222 D. nigra Espirito Santo — Collected by H.N. Whitford, 42, July, 

1918 at the mill of the Société Forestière 

et Industrielle de Collantina; identified 

by S.J. Record, Aug. 6, 1939

SJR 3273 D. nigra Espirito Santo WIS Collected by H.N. Whitford, 76 at 

Collantina, July 1918; identified by S.J. 

Record, Dec. 1, 1940; =MAD10769

SJR 3301 D. nigra Escura, Minas 

Gerais

— Trade sample collected by H.N. Whitford, 

1, 1918; identified by S.J. Record, Dec. 

1, 1940

SJR 3302 D. nigra Escura, Minas 

Gerais

— Trade sample collected by H.N. Whitford, 

2, 1918; identified by S.J. Record, Dec. 

1, 1940

SJR 3303 D. nigra Minas Gerais — Trade sample collected by H.N. Whitford, 

3, 1918

SJR 3508 D. nigra Pedras Pretas, 

Bahia

— Collected by H.M. Curran, 370, 1918

SJR 3509 D. nigra Pedras Pretas, 

Bahia

WIS Collected by H.M. Curran, 370A, 1918; 

identified by Samuel J. Record, 1938

SJR 3525 D. nigra Jequie, Bahia — Collected by H.M. Curran, 386, 1918; 

identified by Samuel J. Record, July, 

1938

SJR 4014 D. spruceana Pará — Museu Goeldi, sample 12

SJR 4146 D. nigra Rio Grongogy, 

Bahia

WIS Collected by H.M. Curran, 6; =MAD7017
Species Verification of Dalbergia nigra and Dalbergia spruceana Samples in the Wood Collection of the Forest Products Laboratory

3

air-dry density and fluorescence under ultraviolet (UV)

light. They concluded that the density of air-dry (6%–7%

moisture content) samples of D. nigra was less than

1 g/cm3

, whereas the density of D. spruceana was greater

than or equal to 1 g/cm3

. Water extract of D. nigra did not

fluoresce, whereas water extract of D. spruceana had a blue

fluorescence. Ethanol extract of D. nigra had greenish-blue

fluorescence, and ethanol extract of D. spruceana had blue

fluorescence.

In the spectrometric method that we used for this study,

direct analysis in real time–time-of-flight mass spectrometry

(DART–TOFMS), ions are created, detected, and analyzed

using a mass spectrometer. The method is described in more

detail in Cody and others (2005, 2012) and Espinoza and 

others (2015), but essentially, the molecules in a wood

sample that is held in an ion stream transfer protons to the

chemical compounds that are encountered in the sample,

producing characteristic protonated signals, which are

directed to the TOFMS. The method requires only that a

sliver of wood be placed between the DART and the

TOFMS inlet for a few seconds, which allows molecules to

be removed from the wood surface and drawn into the mass

spectrometer. Advantages of DART are that it is used in

open air, does not require difficult sample preparation,

needs no radioactive components, and gives instant results

(Cody 2013; Cody and Dane 2010; Cody and others 2005;

Harris and others 2011). It has been used previously to

separate American species of Dalbergia (Lancaster and

Espinoza 2012; Espinoza and others 2015).

The DART–TOFMS spectra are then analyzed statistically

using multivariate analyses such as principal component

analysis (PCA). In its simplest form, PCA attempts to

explain data structure by projecting data onto perpendicular

axes, such that the variability of the data along the first axis

is maximized, and each succeeding axis accounts for the

greatest amount of residual variance. In this way, it attempts

to approximate masses of data by relatively few explainable

components (Johnson and Wichern 2007). Sometimes a

mass of data cannot be simplified in this way. In such a

case, the structure might be simplified by mapping the data

onto coordinate axes that are obtained by a nonlinear

transformation. Kernel principal component analysis

Table 1—Dalbergia nigra and Dalbergia spruceana samples in the Forest Products Laboratory wood collectiona—

continued

Collection No. Species label Location notes Voucher Sample notes

SJR 4230 D. nigra — — Donated to C.M. Richards by a missionary, 

August, 1920; identified by Samuel J. 

Record, Dec. 1, 1940

SJR 4296 D. nigra Catete, Bahia — Donated by Henry J. McCall to E.C.M. 

Richards of NY, 1920; identified by S.J. 

Record, July 1938

SJR 4452 D. nigra — — Donated by the J. H. Monteath Co., NY

SJR 5900 D. nigra — — Donated by C.H. Pearson, NY

SJR 5990 D. nigra — — Donated by W.W. Rowlee, Cornell; 

identified by S.J. Record

SJR 6001 D. nigra — — Donated by W.W. Rowlee, Cornell; 

identified by S.J. Record

SJR 22610 D. spruceana Brazilian 

Amazon

WIS Collected by A. Ducke, 150; received 

January 14, 1933; =MAD31968

SJR 32586 D. nigra — — Donated by the J. H. Monteath Co., NY, 

June 13, 1936; identified by S.J. Record

SJR 36063 D. nigra Espirito Santo — Donated by Paulo F. Souza, Ministerio da 

Agricultura, December 9, 1938

SJR 38188 D. nigra — — Donated by W.J. Hutchinson, NY, June 1, 

1940

SJR 38189 D. nigra — — Donated by W.J. Hutchinson, NY, June 1, 

1940

SJR 38248 D. spruceana Pará — Donated by W.J. Hutchinson, NY, from 

Ministerio da Agricultura, Serviço 

Florestal, Rio de Janeiro, June 1940

SJR 53033 D. nigra Minas Gerais WIS Collected by Col. H.S. Irwin, 2025; 

4.5-cm bark-covered branch or small 

stem

a

Samples labelled MAD are from the Madison collection, and samples labelled SJR are from the Samuel J. Record collection. The collection location, 

voucher, and sample notes give the information included on the Center for Wood Anatomy Research website or in collection files (for the MAD samples), on 

the note cards maintained in the Center for Wood Anatomy Research (for the SJR samples), or from direct observation of the samples. The location of the 

herbarium vouchers for the samples that have them are the University of Wisconsin in Madison (WIS), New York Botanical Garden (NY), Field Museum of 

Natural History, Chicago (F), or Jardim Botânico do Rio de Janeiro (RB). An equal sign before a sample number in the Sample Notes column indicates that a 

duplicate is also included in the MAD or SJR collection.
Research Paper FPL–RP–690

4

(KPCA) is a technique that can perform such a

transformation, thereby revealing structure that is not

revealed by simple PCA and extracting features that are

useful for classification and pattern recognition (Baudat and

Anouar 2000; Hastie and others 2009; Schölkopf and others

1999).

Materials and Methods

A list of all D. nigra and D. spruceana samples at FPL was

compiled using the online database (FPL 2017) for the

MAD samples or by searching the card catalogues for the

SJR samples. The list of samples is given in Table 1,

although not all the samples could be found. All samples

that could be found of the two species were assembled for

examination and measurement.

For the samples for which physical properties were not

previously reported, density was measured as weight in

grams divided by volume in cubic centimeters and volume

was measured by water displacement or with a ruler (or

calipers in the case of veneer thickness). The samples were

all at the ambient equilibrium moisture content (EMC) of

the wood collection. When original densities were

measured, EMC was 6% to 7% (Miller and Wiemann 2006).

In 2012, the wood collection was moved from the fourth

floor to the first floor of the main building at FPL. To see if

the new location had a significant effect on the moisture

content of the wood samples, EMC of a selection of eight

woods was determined by weighing, drying at 103 °C, then

reweighing. The EMC range of these eight woods was 7% 

to 9%.

Water and ethanol fluorescence were measured as described

in Miller and Wiemann (2006). Each fluorescence sample

was prepared by placing a few shavings in a small vial,

adding 2 or 3 mL of water or ethanol, shaking the vial

vigorously, and observing the color of the extract under UV

illumination, using a 100-W, 2-A, long-wave (340–380 nm)

professional UV lamp.

Heartwood samples identified as either D. nigra or

D. spruceana were analyzed using DART–TOFMS. This

was done by holding an approximately 1-mm-thick, 2- to 4-

cm-long wood sliver, split in the longitudinal direction from

a sample block, in the gas stream with no further sample

preparation. Although sapwood samples were included in

the report by Miller and Wiemann (2006), their exudations

require that the mass spectrometer be cleaned frequently.

Therefore, results from sapwood samples are not included in

this study. Dalbergia samples that are entirely sapwood are

usually of no commercial value, although it is common to

find artifacts that include both sapwood and heartwood.

The method used is the same as that described in Espinoza

and others (2015). In summary, mass spectra were acquired

using a DART–SVP ion source (IonSense, Saugus,

Massachusetts) coupled to a JEOL AccuTOF TOFMS

(JEOL USA, Peabody, Massachusetts) in positive ion mode.

Spectra were obtained across the mass-to-charge ratio (m/z)

range of 60 to 1000 at one scan per second. A mass

calibration standard of polyethylene glycol 600 (Ultra,

Kingstown, Rhode Island) was run between samples.

Software from TSSPro3 (Shrader Analytical Labs, Detroit,

Michigan) and Mass Mountaineer (RBC Software, Peabody,

Massachusetts) was used to export files, perform statistical

analyses, and plot results.

Results and Discussion

Table 1 shows the 33 samples labelled Dalbergia nigra and

the six labelled Dalbergia spruceana that are listed as being

in the CWAR collection. Two of these could not be found

(SJR3508 and SJR4146), two were all sapwood (samples 20

and 34), and one was a 4.5-cm-diameter sapwood branch

(sample 33).

Figure 1 is a heat map for Dalbergia heartwood samples.

Caviunin, with m/z of 375 (374.346; ILDIS and CHCD

1994b), is prominent in D. nigra but faint or absent in

D. spruceana, and elemicin, with m/z of 208 (208.257;

ILDIS and CHCD 1994b), is present in D. spruceana but

not in D. nigra.

Table 2 gives the air-dry density, fluorescence response, and

DART–TOFMS results of each sample tested. The identity

of each sample for each test is also given, in plain font when

it is the same as that listed by the wood collection data

(Table 1), in bold when it is different, or as a question mark

when the test was inconclusive.

The results of the KPCA are plotted in Figure 2. Only the

first two principal components (PC1 and PC2) are plotted,

but they are sufficient to separate the data into interpretable

groups. Samples with PC1 values greater than 0 were

D. nigra, and samples with PC1 values less than –0.4 were

D. spruceana. Two samples, 15 and 29, had PC1 values of

–0.17 and –0.25, respectively. Therefore, it was not clear to

which species they should be assigned (Table 2).

The results of the PCA are plotted in Figure 3. As in

Figure 2, only the first two principal components (PC1 and

PC2) are plotted. Visually, the separation provided by the

PCA is better than that provided by the KPCA. In the PCA

case, after samples 12, 27, and 28 were corrected (we

believe) to D. spruceana, the D. nigra samples all had PC1

values of less than 1.3, whereas the D. spruceana samples

all had PC1 values of greater than 4.7.

For KPCA, the first principal component accounted for 20%

of the variability in the data, the second accounted for

another 11%, and a third accounted for 9%. For PCA, the

first principal component accounted for 33% of the

variability in the data, the second accounted for another

15%, and the third accounted for another 9%. Based on the

proportions of the data explained by the principal
Species Verification of Dalbergia nigra and Dalbergia spruceana Samples in the Wood Collection of the Forest Products Laboratory

5

components and by comparison of the separations seen in

Figures 2 and 3, we concluded that the kernel approach did

not result in a better separation of the two species.

Most of the samples were judged, on all tests, to be as

originally identified (Table 2). Some, however, were not.

Three unvouchered samples, 12, 27, and 28, labelled as

D. nigra, were all identified as D. spruceana by density,

water fluorescence, ethanol fluorescence, and DART–

TOFMS (Table 2). Therefore, we concluded that they were

misidentified when they were added to the SJR wood

collection (Table 2). They were all trade (nonvouchered)

samples identified by Samuel J. Record based on wood

anatomy (Table 1). Sample 27 (SJR5990) was also tested by

Kite and others (2010) and found to lack dalnigrin but to

contain pseudobaptigenin, also indicating that it is not

D. nigra but rather D. spruceana.

Sample 9, labelled D. nigra and also unvouchered, had the

density of D. spruceana but the water fluorescence, ethanol

fluorescence, and DART–TOFMS results, including the

prominent peaks of caviunin and dalnigrin, characteristic of

D. nigra (Table 2; Fig. 4). Miller and Wiemann (2006)

concluded that this sample was D. spruceana, based mainly

on density, although they recognized that it had the

fluorescence of D. nigra. The sample came from the Field

Museum and has a collector’s number (Hildebrand 17;

Table 1), but it is unknown if it was identified based on

floral or vegetative material or was a trade sample identified

only on wood characteristics. It has the mixture of

vasicentric, aliform, diffuse-in-aggregates, and apotracheal

banded parenchyma that is characteristic of the genus

Dalbergia. A comparison of the spectrum of the sample

with the spectra of two vouchered samples of D. nigra

(samples 1 and 10; Fig. 4) shows that their spectra are very

similar. Therefore, we concluded that sample 9 is in fact

D. nigra and that the conclusions of Miller and Wiemann

(2006) (that it was misidentified) were incorrect.

Figure 4 shows prominent peaks for three D. nigra samples

(1, 9, and 10), corresponding to the phenolic compound

dalnigrin and isoflavone caviunin, which are abundant in the

heartwood of D. nigra but not D. spruceana (ILDIS and

CHCD 1994a; Kite and others 2010). Although Kite and 

others (2010) reported that dalnigrin is unique to D. nigra,

the sample of D. spruceana also showed a smaller peak at

the same m/z value. This peak probably corresponded to a

different compound with a similar m/z, and chromatography

is needed to differentiate between such isomers that cause

confusion in interpretation of the DART–TOFMS results.

Figure 1. Graphical representation (heat map) of the 

spectral results comparing the heartwood of Dalbergia 

nigra (24 samples, between blue line and red line) with 

that of Dalbergia spruceana (seven samples, below red 

line). The abscissa, m/z, is the mass-to-charge ratio of 

the compound detected (its molecular mass divided by 

its electrical charge), and the ordinate contains the 

individual samples. The compound elemicin, indicated by 

the arrow on the left, is prominent in D. spruceana but 

faint or absent in D. nigra. The compound caviunin, 

indicated by the arrow on the right, is prominent in 

D. nigra but faint or absent in D. spruceana.

Figure 2. Values of the first two principal components 

(PC1 and PC2) extracted using kernel principal 

component analysis (KPCA) for each of the Dalbergia

samples analyzed using direct analysis in real time–time 

of flight mass spectrometry (DART–TOFMS). Numbers 

above or below open circles refer to sample numbers in 

Table 2.
Research Paper FPL–RP–690

6

Table 2—Heartwood samples identified as Dalbergia nigra or Dalbergia spruceana using density, water fluorescence, 

ethanol fluorescence, or DARTa

Density Water fluorescence Ethanol fluorescence DART, PCA DART, KPCA

Sample 

number

Wood 

collection 

number

Value 

(g/cm3)

Species 

from 

density Color

Species from 

fluorescence Color

Species from 

fluorescence

Projection 

onto PC1

Species by 

DART, 

PCA

Projection 

onto PC1

Species by 

DART, 

KPCA

Samples labelled Dalbergia nigra

1 MAD7017b 0.96 D. nigra none D. nigra greenish blue D. nigra –5.2349 D. nigra 0.2580 D. nigra

2 MAD10769c 0.79 D. nigra none D. nigra greenish blue D. nigra –1.4813 D. nigra 0.4026 D. nigra

3 MAD13091 0.76 D. nigra none D. nigra greenish blue D. nigra 0.5032 D. nigra 0.1792 D. nigra

4 MAD21010 0.85 D. nigra none D. nigra greenish blue D. nigra –5.4438 D. nigra 0.4029 D. nigra

5 MAD23334 0.97 D. nigra none D. nigra greenish blue D. nigra –2.3060 D. nigra 0.0131 D. nigra

6 MAD31954 0.82 D. nigra none D. nigra greenish blue D. nigra –3.8667 D. nigra 0.4600 D. nigra

7 MAD31955 0.86 D. nigra none D. nigra greenish blue D. nigra –2.3705 D. nigra 0.4201 D. nigra

8 MAD31956 0.88 D. nigra none D. nigra greenish blue D. nigra –1.6756 D. nigra 0.3909 D. nigra

9 MAD31957d 1.01 D. spruceana none D. nigra greenish blue D. nigra –2.3950 D. nigra 0.0288 D. nigra

10 MAD31958 0.66 D. nigra none D. nigra greenish blue D. nigra –1.8438 D. nigra 0.1856 D. nigra

11 SJR550e 0.75 D. nigra none D. nigra greenish blue D. nigra –4.9774 D. nigra 0.2692 D. nigra

12 SJR1442 1.11 D. spruceana blue D. spruceana blue D. spruceana 5.0931 D. spruceana –0.6711 D. spruceana

13 SJR3107 0.84 D. nigra none D. nigra greenish blue D. nigra –2.7503 D. nigra 0.2107 D. nigra

14 SJR3222 0.82 D. nigra none D. nigra weak greenish 

blue

D. nigra 0.3578 D. nigra 0.1989 D. nigra

15 SJR3273f 0.81 D. nigra none D. nigra greenish blue D. nigra 1.2837 D. nigra –0.1687 ?

16 SJR3301 0.84 D. nigra none D. nigra greenish blue D. nigra –3.0526 D. nigra 0.0139 D. nigra

17 SJR3302 0.93 D. nigra none D. nigra greenish blue D. nigra –2.5575 D. nigra 0.2716 D. nigra

18 SJR3303 0.80 D. nigra none D. nigra greenish blue D. nigra –-0.2419 D. nigra 0.2022 D. nigra

19 SJR3508 0.80 D. nigra none D. nigra greenish blue D. nigra — — — —

20 SJR3509g 0.72 D. nigra — — — — — — — —

21 SJR3525 0.79 D. nigra none D. nigra greenish blue D. nigra –3.3547 D. nigra 0.3732 D. nigra

22 SJR4146h 0.90 D. nigra none D. nigra greenish blue D. nigra — — — —

23 SJR4230 0.88 D. nigra none D. nigra greenish blue D. nigra –1.5035 D. nigra 0.1065 D. nigra

24 SJR4296 0.81 D. nigra none D. nigra greenish blue D. nigra –2.2327 D. nigra 0.3417 D. nigra

25 SJR4452 0.98 D. nigra none D. nigra greenish blue D. nigra –2.2954 D. nigra 0.0893 D. nigra

26 SJR5900 0.85 D. nigra none D. nigra greenish blue D. nigra –5.0023 D. nigra 0.0927 D. nigra

27 SJR5990i 1.01 D. spruceana blue D. spruceana blue D. spruceana 9.9405 D. spruceana –0.5949 D. spruceana

28 SJR6001 1.06 D. spruceana blue D. spruceana blue D. spruceana 8.5320 D. spruceana –0.6631 D. spruceana

29 SJR32586j 0.79 D. nigra none D. nigra yellow-green ? 1.2226 D. nigra –0.2489 ?

30 SJR36063 0.93 D. nigra none D. nigra greenish blue D. nigra –2.5146 D. nigra 0.1427 D. nigra

31 SJR38188 0.83 D. nigra none D. nigra greenish blue D. nigra –0.9718 D. nigra 0.1611 D. nigra

32 SJR38189 0.92 D. nigra none D. nigra greenish blue D. nigra –3.0590 D. nigra 0.1254 D. nigra

33 SJR53033k — — — — — — — — — —

Samples labelled Dalbergia spruceana

34 MAD18588g 0.80 D. nigra — — — — — — — —

35 MAD31968l 0.86 D. nigra blue D. spruceana blue D. spruceana 8.4813 D. spruceana –0.6261 D. spruceana

36 SJR1430 1.00 D. spruceana weak blue D. spruceana blue D. spruceana 4.7688 D. spruceana –0.4311 D. spruceana

37 SJR4014 1.00 D. spruceana blue D. spruceana blue D. spruceana 6.2695 D. spruceana –0.5540 D. spruceana

38 SJR22610m 0.85 D. nigra blue D. spruceana blue D. spruceana 8.0297 D. spruceana –0.6626 D. spruceana

39 SJR38248 1.05 D. spruceana blue D. spruceana blue D. spruceana 6.6490 D. spruceana –0.7198 D. spruceana

a

Density and fluorescence from Miller and Wiemann (2006) or measured. Species determined from physical property tests or spectroscopic method in italic font when it is the 

same as sample label and in bold italic when it is different. A question mark indicates that the test did not suggest a species. Projections onto principle component 1 (PC1) axis are 

based on direct analysis in real time (DART) results that extract three axes (PCA, principal component analysis; KPCA, kernel principal component analysis). b

Sample from same tree as SJR4146.

c

Sample from same tree as SJR3273; 20% sapwood. d

20% sapwood; spectrograph with huge caviunin peak.

e

Veneer.

f

Sample from same tree as MAD10769; 80% sapwood. g

100% sapwood.

h

Sample from same tree as MAD7017; sample not tested by DART.

i

10% sapwood.

j

Ethanol fluorescence test indeterminate.

k

Bark-covered; 100% sapwood; sample not tested. l

Sample from same tree as SJR22610; 30% sapwood.

mSample from same tree as MAD31968; 40% sapwood.
Species Verification of Dalbergia nigra and Dalbergia spruceana Samples in the Wood Collection of the Forest Products Laboratory

7

Sample 29, an unvouchered sample labelled D. nigra, had a

yellow–green ethanol extract fluorescence; this color was

not found in any other sample. Density, water extract

fluorescence, and PCA all pointed to D. nigra, but the

KPCA PC1 value was intermediate between the values for

D. nigra and D. spruceana (Table 2; Fig. 2). Inconsistent

fluorescent results are not uncommon. Miller (2007) found

variability in the presence, color, and intensity of surface

fluorescence in many of the 1400 fluorescent species that he

tested. For water and ethanol extract fluorescence, Wiemann

and Ruffinatto (2012) found differences in color and

intensity among samples of D. stevensonii Standl. and

D. tucurensis Donn. Sm., even when pairs of samples were

collected from the same tree. A near infrared spectroscopy

comparison of sample 29 with samples of D. nigra and five 

other species of Dalbergia determined it to be D. nigra

(Pastore 2017).

The other sample with inconclusive KPCA results was

sample 15. However, all other tests point to it being

correctly identified as D. nigra. Therefore, we concluded

that the natural variability of the KPCA accounts for the

lack of a clear separation.

Samples 15 and 29 both plotted near each other in Figures 2

and 3 (KPCA and PCA, respectively), their densities are

similar (0.81 and 0.79, respectively; Table 2), and their PCA

PC1 values are closer to those of D. nigra than

D. spruceana. Therefore, we concluded that they are both

D. nigra.

Samples 34, 35, and 38 were all vouchered samples labelled

as D. spruceana (Table 1), but their densities indicated that

they were D. nigra (Table 2). Sample 34 was entirely

sapwood; therefore it was not tested by fluorescence or

DART–TOFMS. Samples 35 and 38 came from the same

Figure 3. Values of the first two principal components 

(PC1 and PC2) extracted using principal component 

analysis (PCA), for each of the Dalbergia samples 

analyzed using direct analysis in real time–time of flight 

mass spectrometry (DART–TOFMS). Numbers above or 

below open circles refer to sample numbers in Table 2.

Figure 4. Comparison of direct analysis in real time–time of flight mass spectrometry (DART–TOFMS) mass spectrum of 

unvouchered Dalbergia nigra sample 9 (top, blue) with the spectra of two vouchered D. nigra samples, sample 1 (second 

from top, red) and sample 10 (third from top, green), and vouchered sample 35 of D. spruceana (bottom, yellow). Each peak 

corresponds to an ion that was detected in the wood sample. The abscissa, m/z (mass-to-charge ratio), is the molecular 

weight of an ion divided by its charge number, and the ordinate is the relative signal intensity of the ions. The compounds 

dalnigrin and caviunin, found in the D. nigra samples, are indicated by the labelled arrows. In D. spruceana, two much 

smaller peaks are found at the same m/z values, but these are not dalnigrin or caviunin (Kite and others 2010).
Research Paper FPL–RP–690

8

tree. Their densities were almost the same (0.86 and 0.85,

respectively) and corresponded to the typical density of

D. nigra (Table 2). But their blue water and ethanol

fluorescence indicated that they were D. spruceana. Their

principal components projections, indicated by open red

circles on the left side of Figure 2 (KPCA) and the right side

of Figure 3 (PCA), were clearly in the D. spruceana area.

Therefore, we concluded that they were low-density

samples of D. spruceana.

Comparison of matching samples from the MAD and SJR

collections (Table 2) gives an idea of the similarity of

DART–TOFMS results that can be expected within a tree.

Figure 5 shows the PCA PC1 and PC2 coordinates of all of

the samples. D. nigra samples 2 and 15 and D. spruceana

samples 35 and 38 are indicated by large circles. The

coordinates of the two D. spruceana samples are very close,

but those of D. nigra are more widely separated. Both sets

of samples contain sapwood, but the size and shape of the

blocks resulted in the slivers for the DART–TOFMS being

sampled differently with respect to the heartwood–sapwood

transition. In both D. spruceana samples, slivers were taken

about 4 cm from the transition. For the D. nigra samples,

however, a sliver was taken about 3 cm from the transition

in sample 15 (right side of the vertical axis in Fig. 5) but

only about 1 cm from the transition in sample 2 (left side of

the vertical axis in Fig 5). Thus, it is possible that a

difference in the chemical composition of the heartwood

because of age might be a factor in the results from the

DART–TOFMS analysis. Hillis (1999) states that amounts

and types of extractives vary across the heartwood zone

because of change in rate of conversion of precursors to

extractives, change in solubility with age, and changes in

hydrolysis, polymerization, and pH with time.

All heartwood samples determined to be D. nigra contained

caviunin (m/z = 375 on the heat map; Fig. 1), but only three

of the D. spruceana heartwood samples showed traces of

caviunin (samples 36, 38, and 35). Caviunin is reported to

be found in D. nigra wood (Gottlieb and Magalhães 1961)

and D. spruceana sapwood (Cook and others 1978), as well

as in the wood of D. barretoana Hoehne, D. inundata

Benth., and D. villosa (Benth.) Benth. from Brazil (ILDIS

and CHCD 1994a), D. paniculata Roxb. from Asia

(Adinarayana and others 1971), the root and bark of the

shrub D. spinosa Roxb. from Asia (ILDIS and CHCD

1994a), and the heartwood of D. tucurensis Donn. Sm.

(Espinoza and others 2015). Two of the D. spruceana

samples with traces of caviunin contained sapwood

(samples 35 and 38). The third sample (sample 36) was a

trade sample cut from a piece of shaped molding, without

sapwood. It is possible that proximity to sapwood may be

the reason for caviunin in samples 35 and 38, although the

slivers tested were heartwood. The presence of caviunin in

sample 36 is unexplained; however, its water extract

fluorescence was weak blue rather than the blue color

typical of D. spruceana (Table 2) and its projection onto

PCA PC1 and PC2 (4.769, –6.996) (Table 2; Fig. 3) showed

it as an outlier compared with the other samples of

D. spruceana. It was not an outlier when compared using

KPCA, but it plotted closer to the D. nigra samples than any

other sample of D. spruceana (–0.431, –0.071; Table 2;

Fig. 2). It is possible that the sample is neither D. nigra nor

D. spruceana.

Conclusions

If a heartwood sample of Dalbergia is known to be either of

the Brazilian look-alike species D. nigra or D. spruceana,

CITES-protected D. nigra can usually be distinguished from

unprotected D. spruceana based on density, water

fluorescence, and ethanol fluorescence. However, in some

cases, these physical characteristics give erroneous or

ambiguous results. Based on the criteria of Miller and

Wiemann (2006), density seemed anomalously high in four

samples labelled D. nigra (9, 12, 27, and 28), density 

seemed anomalously low in three samples labelled

D. spruceana (34, 35, and 38), and the fluorescence color of

the ethanol extract of one sample of D. nigra (29) was

completely different from that found in any other sample.

DART–TOFMS confirmed the identity of all but three of

the samples (12, 27, and 28). Therefore, we concluded that

Figure 5. Principal components map for the principal 

components analysis (PCA) based on the direct analysis in 

real time–time of flight mass spectrometry (DART–TOFMS) 

spectra; PCA PC1 is the first principal component, PCA 

PC2 the second. Large symbols and labels indicate the 

paired (MAD and SJR) Dalbergia samples. Black symbols 

are for D. nigra samples, and red symbols are for 

D. spruceana. Numbers refer to sample numbers in 

Table 2.
Species Verification of Dalbergia nigra and Dalbergia spruceana Samples in the Wood Collection of the Forest Products Laboratory

9

the physical property differences found in the others were 

caused by interspecific variability.

The DART–TOFMS method, using PCA, is reliable, based

on results from this study and the study by Espinoza and 

others (2015). PCA of the spectra confirmed the identity of

all MAD samples tested by this method (ten D. nigra and

one D. spruceana). For the SJR samples, the method

confirmed the identity of 16 D. nigra and four D. spruceana

samples but determined that three samples labelled D. nigra

were, in fact, D. spruceana.

Kukachka’s decision to discard doubtful samples improved

the accuracy of the collection, but the retention of all

samples by Yale means that we now have more samples

available of a now-restricted species (D. nigra). Under the

assumption that all tested samples are either D. nigra or

D. spruceana, it also added three reliably identified samples

of under-represented D. spruceana.

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