Dalbergia Congestiflora Standl.: Wood Structure

lAWA Journal, Vol. 17 (3), 1996: 327-341

DALBERGIA CONGESTIFLORA STANDL.: WOOD STRUCTURE AND PHYSICO-CHEMICAL PROPERTIES COMPARED WITH OTHER CENTRAL AMERICAN SPECIES OF DALBERGIA 1 by Hans Georg Richter, Vlf-Joachim Krause & Claudia Muche Institute for Wood Biology and Wood Protection, Federal Research Centre for Forestry and Forest Products, LeuschnerstraBe 91, 21031 Hamburg, Germany

SUMMARY

Wood structure and selected physico-chemical properties of a rare Mex• ican species, tentatively identified as Dalbergia congestiflora, are describ• ed and compared with other Central American species of Dalbergia. On account of their distinct wood structure, four species groups can be distinguished: 1) D. granadillo, D. hypoleuca, D. lineata and D. retusa (,cocobolo') are characterised by mainly apotracheal diffuse-in• aggregates parenchyma, large and few vessels, high density (0.89-1.35 g/cm3), identical heartwood colour, and chemical composition of ex• tractives (D. granadillo, D. retusa); 2) D. tucuruensis (including D. cubit• quitzensis) and D. palo-escrito are identical in all aspects but distinct from the coco bolo group on account of differences in parenchyma dis• tribution, heartwood colour and extractives composition (D. tucuruensis), and the consistently lower density (~0.80 g/cm3); 3) D. congestiflora and D. funera (= D. calderonii) differ markedly in heartwood colour and somewhat in heartwood extractives composition but share a high den• sity and similar wood structural pattern characterised primarily by rela• tively small and frequent vessels, banded parenchyma and the presence of prismatic crystals in ray cells; 4) D. stevensonii is very similar in wood structure to D. tucuruensis but has a much higher density and different heartwood extractives composition. These results indicate that the combination of wood structure and chemistry of heartwood extractives may be successfully employed for intrageneric classification of Dal• bergia. Key words: Dalbergia, wood anatomy, density, extractives, identification.

INTRODUCTION

Wood species of the pantropical genus Dalbergia L. f. have long commanded consid• erable attention in local and international timber markets. Because of their outstanding beauty and excellent physical and mechanical properties, some have been known in the trade for more than 300 years as preferred timbers for all kinds of cabinet work and

1) Dedicated to Prof. Dr. Dr. h. c. Walter Liese on the occasion of his 70th birthday.

Downloaded from Brill.com10/06/2021 10:25:09AM via free access 328 IAWA Journal, Vol. 17 (3),1996 fine furniture, cutlery, and musical instruments, Of the approximately 100 species of Dalbergia trees and shrubs distributed throughout the tropical regions of the world (Mabberley 1987), some 10 to 15 are among the most valuable trade timbers, e.g.: Brazilian rosewood (D. nigra Fr. Allem.) from northeastern Brazil, now protected under the CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) agreement where it has been listed in Appendix I since 1992; Indian rosewood or sonokeling (D. latifolia Roxb.) from India and Indonesia; African blackwood (D. melanoxylon Guill. & Perr.) from Central and Eastern Africa. Central America has been the traditional and sole supplier of cocobolo (mainly D. retusa HemsI., D. granadillo Pittier) with a combined range from southern Panama to southwestern Mexico. Two additional species, D. hypoleuca Pittier and D. lineata Pittier, are thought to be closely related to D. retusa and might have contributed some timber to the cocobolo trade (Record & Garrat 1923). Other Central American species in the international market are Honduras rosewood (D. stevensonii StandI.) from Belize, Guatemala and southeastern Mexico and, more recently, granadillo rojo [D. tucuruensis Donn. Sm., including D. cubilquitzensis (Donn. Sm.) Pittier] from Guatemala and Honduras. Dalbergia calderonii StandI. (including D.funera StandI.) and the recently (1988) de• scribed D. palo-escrito Rzedowski & Guridi from Mexico are only of local signifi• cance. For all the demand, supplies were always more or less restricted due to the low frequency, small dimensions and often irregular growth of the trees, and prices were correspondingly high. Traders and manufacturers in Europe and elsewhere are, there• fore, more conscious about shipments of Dalbergia timbers being true to order than is common with general utility timbers. Hence, a thorough knowledge of botanical iden• tity and corresponding trade names of the respective species or species groups is essential to satisfy the specific trade requirements. Therefore the present study was undertaken with the objective to provide safe identification of Central American Dalbergia species and species groups by means of general, macroscopic and micro• scopic features amended by information on the chemical composition of heartwood extractives.

MATERIALS AND METHODS

In 1983, a German importer called the attention of the senior author to a cocobolo shipment from Mexico as it contained a log which, on account of its intensely violet heartwood colour, was singled out as definitely different from the usually deep yellow• ish to orange brown of cocobolo. The wood structure ofthis specimen (RBHw 19195) indicated Dalbergia, yet was distinct from any of the cocobolo producing species. Since no matching specimen was available from the RBHw and other major wood collections, and as at that time no matching wood description could be found in litera• ture, its identity was uncertain. In 1987, the senior author was informed by a carpenter in Mexico that a timber fitting the given description was locally known as 'camotillo', and was occasionally used by artisans in the region. During an adventurous one-week search in the coastal regions of Colima and Jalisco, wood and herbarium specimens (fruiting) were collected from a small camotillo tree (RBHw 18732); one additional

Downloaded from Brill.com10/06/2021 10:25:09AM via free access Richter, Krause & Muche - Wood of Dalbergia congestiflora 329 wood specimen (RBHw 18731) was found in the trash of a Manzanillo (Colima) saw• mill, another was obtained later from a Guadalajara (Ja1isco) craftsman (RBHw 18276). Based on matching herbarium specimens deposited at the Instituto de Bio10gia, Universidad de Guadalajara, the collected material (RBHw 18732) was tentatively identified as Dalbergia congestiflora Pittier. The subsequent comparative wood anatomical analysis of Central American spe• cies of Dalbergia includes the following species and specimens, respectively:

Dalbergia tucuruensis (including D. cubilquitzensis): RBHw 13987 (commercial), Honduras; RBHw 16326 (commercial), Mexico; RBHw 18243 (= USw 7387, commercial), Honduras; RBHw 18247 (= USw 19375, Frejnik 540), Belize; RBHw18252 (= USw 2892 = SJRw 8896, Kuylen s.n.), Guatemala; RBHw 18255 (commercial), Honduras; RBHw 18277 (commercial), Honduras; RBHw 18396 (= MADw 31975 = SJRw 10729, Galusser s.n.), Guatemala; RBHw 18397 (= MADw 10836 = SJRw 3721, Whitford & Stadtmiller 61), Guatemala; RBHw 18398 (=MADw 11011 = SJRw 8896, KuylenG65), Guatemala. -D.funera: RBHw 18534 (= SJRw 47207, Calderon 2479, type specimen), Mexico. - D. granadillo: RBHw 1484 (commercial), Mexico; RBHw 18395 (= SJRw 38303, Hutchinson s.n.), Nicaragua. - D. hypoleuca: RBHw 4787,4788,4789 (commercial), Costa Rica. -D.lineata: RBHw 18533 (= SJRw 7493, Calderon s.n.), Salvador. - D. palo-escrito: RBHw 19765 (= GUAw 144, vouchers deposited at lnst. Ecologia, Morelia, Mexico), Mexico. - D. retusa: RBHw 546, 4801,4802 (commercial), Nica• ragua; RBHw 4807 (commercial), Honduras; RBHw 16229, 16245 (Poveda 268,355), Costa Rica; RBHw 18244 (= USw 9, Pittier 3511), Panama; RBHw 18245 (= USw 4231, commercial), Costa Rica; RBHw 18248 (= USw 15707, Forgeson & Southwell 32A), Panama; RBHw 18250 (= USw 19303, Belize For. Dept. 468), Belize; RBHw 18275 (= SJRw 5344, Fait s.n.), Costa Rica; RBHw 18365 (commercial), Guatemala; RBHw 18393 (= SJRw 8903, commercial), Gua• temala; RBHw 18394 (= SJRw 4764, Reko 3517), Mexico. - D. stevensonii: RBHw 1356, 4806 13048 (commercial), Honduras; RBHw 10840 (= USw 10956, Belize For. Dept. 178), Belize.

Terminology and the methods for determining quantitative features conform to the recommendations from the IAWA feature list (IAWA Committee 1989); each vessel was counted individually for vessel frequency, intervessel pit diameters were meas• ured vertically.

In addition to wood structure the following characteristics were determined: - Density at 6-8% me; values from literature were adjusted according to a standard graph (IAWA Committee 1981). Heartwood fluorescence with shortwave (254 m) and longwave (365 m) ultraviolet light (lAWA Committee 1989). - Colour and fluorescence of ethanol extract (lAWA Committee 1989). - Extractives content of selected specimens (Soxleth ethanol extraction according to Weis 1981). - Froth test (IAWA Committee 1989). - Thin-layer chromatography of ethanol extract: Aluminium oxide covered TLC plates with fluorescence indicator F 254 (type E), MERCK company; 0.01 ml extract segregated with eluation solvent (formic acid-acetic acid ethyl ester-chloroform 1 : 4 : 5); number and position of segregated compounds, fluorescence under short• wave and longwave UV-light (Weis 1981).

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Fig. 1. Dalbergia congestiflora. a & b: transverse and tangential section (scale bar = 0.5 mm); c: radial section (scale bar = 0.2 mm); d: prismatic crystals in ray cells (long arrows) and axial parenchyma (short arrow) (scale bar = 0.1 mm).

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RESULTS AND DISCUSSION

General information on Dalbergia congestiflora The species was first described by Pittier (1922) based on a single specimen (Pringle 6981) collected at Cuernavaca in the Mexican state of Morelos. Later collections were made in the states of Oaxaca, Colima and Jalisco. According to Barajas-Morales and Leon Gomez (1989) the tree is also found in the states Pueblo, Guerrero and Michoacan where it is known as 'campinzeran' (also spelled campinchiran, tampinzeran). Thus the presently known distribution appears to encompass a stretch along the Mexican Pacific coast from Oaxaca to Jalisco, reaching inland for approximately 250 km, at altitudes from 100 to 1650 metres. Rudd (personal comm. 1995), judging from an ex• tensive study of material including collections from southern Mexico (Chiapas), came to the tentative conclusion that "perhaps the circumscription of D. congestiflora should apply only to the specimens from central Mexico (states of Morelos and Mexico). The collections from the states of Jalisco, Michoacan, Guerrero, and southward that I pre• viously thought were referable to D. congestiflora ... might represent an undescribed species." However, notwithstanding possible future changes as indicated by Rudd, the present botanical attribution is maintained in this paper. Dalbergia congestiflora is a species of the tropical to montane deciduous forests of western Mexico characterised by a dry climate with an annual precipitation of ± 600 mm. The trees are usually less than 10 m, most commonly 3-8 m high with a diameter of 15-20 cm, rarely more. Often several trunks emerge from a single stump. The spe• cies appears to be extremely rare. According to dependable local (Colima) sources, for every hundred trees of cocobolo (D. granadillo) there are only two of camotillo (D. congestiflora).

Wood description The description of D. congestiflora is based on three commercial (RBHw 18276, 18731,19195) and one vouchered specimen (RBHw 18732 = GUAw 1); vouchers are deposited at the Instituto de Biologia, Universidad de Guadalajara, Jalisco, Mexico. General features - Sapwood cream to yellowish white, heartwood intensely violet when fresh, darkening to a purplish brown with age; attractively figured due to lighter coloured streaks and arcs (banded axial parenchyma, Fig. 2a); wood very hard and heavy (0.94-1.23 g/ cm3); planed surfaces dense and slightly lustrous; grain generally straight to sometimes weakly interlocked; fresh heartwood with a faint fragrance fad• ing upon drying. Growth increment boundaries generally indistinct. Vessels - Wood diffuse-porous with considerable variation in vessel frequency and size; vessels solitary and in radial multiples of 2-5 (Fig. la); number of vessels varying from 5-1O/mm2; average tangential diameter (25 largest vesflels of each specimen) 100-170 !JIll; however, the diameter of the smallest vessels may be around 20 !JIll, that of the largest 240 !JIll (RBHw 18731); vessel member length (± 200 !JIll; perforations simple and nearly horizontal, intervessel pits in a loosely alternate ar• rangement, 5-7 !JIll in diameter (vertical dimension), vestured; rose-coloured to brown• ish violet deposits frequent in vessel lumina.

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Fibres - Short (c. 700 ~) and thick-walled, with small (± 2 ~) and inconspic• uously bordered pits mainly confined to radial walls (= libriform fibres sensu Baas 1986); central parts in horizontal seriation with storied parenchyma and rays; non• septate; in zones of intense coloration lumina with gum deposits of the same colour as in vessels. Axial parenchyma - Variable in type, quantity and distribution; in adult wood predominantly in anastomosing, sometimes broken tangential bands, 1-4 cells wide, interspersed with continuous marginal bands mostly 2 cells in width (Fig. 1a); also paratracheal sparse to aliform, often extending into delicate lateral wings; occasion• ally apotracheal diffuse-in-aggregates as short uniseriate lines or small cell clusters; in early-formed wood (RBHw 18732) the paratracheal and apotracheal types are well developed, banded parenchyma only weakly so. Parenchyma fusiform and in strands of 2 (or 3) cells, in horizontal seriation with storied rays, vessel members and fibres. Prismatic crystals in chambered crystalliferous strands, most frequent in those of the marginal bands (Fig. 1c). Rays - Very fine and numerous, averaging 11-16/mm; in mature wood mostly biseriate (Fig. 1b) with scattered uni- and triseriate rays, in juvenile wood (RBHw 18732) predominantly uniseriate; 5-7 cells high (100-130 ~), in juvenile wood up to 13 cells; composed of procumbent cells throughout, marginal cells often irregularly shaped and larger (yet still procumbent) than body cells; vessel-ray pits similar to intervessel pits in size and shape; rays distinctly storied (Fig. 1b), 6 tiers/mm; pris• matic crystals in body and marginal cells (Fig. 1d) observed in all specimens except RBHw 18732. Other features - Heartwood non-fluorescent; colour of ethanol extract deep violet, suggesting that of red beet (hence the local name of camotillo which is derived from 'camote', a Mexican plant with edible roots similar to red beet); ethanol extract weakly fluorescent, blue-green; froth test positive; thin-layer chromatography yielded a total of 11 components (spots), two of which had a bright blue fluorescence (for details see next section).

Species differentiation No detailed wood anatomical descriptions of the Central American species of Dalbergia covered by this study are presented as most have been described elsewhere (Record & Garrat 1923; Gottwald 1958; Rzedowski & Guridi 1988; Berti Nardi & Edlmann Abbate 1992). Rather, only characters of diagnostic significance are sum• marised in Table 1.

Fig. 2. a: Tangential surface of Dalbergia congestiflora with colour variegation due to alternating light parenchyma and dark fibre zones (about half natural size); b-f: line drawings of transverse surface, highlighting vessel and axial parenchyma distribution. - b: Dalbergia congestiflora. - c: D. funera. - d: D retusa. - e: D. tucuruensis. - f: D. stevensonii. All scale bars = 0.5 mm.

Downloaded from Brill.com10/06/2021 10:25:09AM via free access VJ VJ Table 1. Selected qualitative and quantitative features of Central American species of Dalbergia. 01>-

D. congestiflora D·funera D. granadillo D. stevensonii D. tucuruensis D. hypoleuca D. palo-escrito D. lineata D. retusa

Trade name 'camotillo' 'funera' 'cocobolo' 'Honduras rosewood' 'granadillo rojo'

Heartwood colour dark violet-brown yellow-brown yellow to orange to medium to dark yellow-brown to variegated dark brown with pinkish brown, brown, with or dark streaks with dark streaks without dark streaks

Odour of dry heartwood negative negative fragrant negative negative

Density (g/cm 3) 0.94-1.23 ± 1.10 0.90-1.35 0.93-1.17 0.65-0.82

Intervessel pit diameter (J.UI1) 5-7 5-7(-8) 8-10 8-10 8-10

Vessel diameter (J.UI1) 100-165(-240) ± 110(-180) ± 200(-330) ± 220(-350) ± 270(-450) (maximum values) ...... Downloaded fromBrill.com10/06/2021 10:25:09AM Vessel frequency (nr./mm2) 5-10 10-15 3-6 3-6 3-6 ~ :> ...., 0 Dominant parenchyma pattern banded (1- 3-seriate) banded (2-5-seriate) apotracheal diffuse- paratracheal vasi- paratracheal vasi- ~ in-aggregates centric to aliform + centric to aliform + 8 ('reticulate' ) confluent confluent ?

~ negative yellowish green negative negative negative ..... Heartwood fluorescence -J ,...., Colour of ethanol extract deep violet light yellow shades of yellow, light yellow to light yellow to ~ via freeaccess ..... orange, brown light pinkish brown light brown '-0 '-0 0'\ Richter, Krause & Muche - Wood of Dalbergia congestiflora 335

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Fig, 3, Thin-layer chromatogram of heartwood ethanol extracts of 6 Central American Dalbergia species. Numerical codes represent different colours: 1 = brown; 2 = greyish blue; 3 = bright blue; 4 = orange; 5 = yellow; 6 = grey. Strong fluorescence under ultraviolet light is indicated by *, weak fluorescence by (*).

Heartwood colour - Dalbergia congestiflora is easily differentiated from all other Central American Dalbergia species studied by its strikingly violet heartwood colour in combination with a subtle surface variegation caused by the sequence of light-col• oured parenchyma bands (Fig. 2a). Some colour variation and almost black streaks were observed only in the first-formed heartwood of a young tree (RBHw 18732). Odour - Some of the commercialised Dalbergia species, e. g., Brazilian rosewood (D. nigra) or Indian rosewood (D. latifolia), are known for retaining an aromatic or spicy odour after drying. The timber of most of the Central American species studied are slightly to strongly aromatic when fresh, but only those of the cocobolo group retain their fragrance, commonly described as 'cinnamon-like' or 'pleasantly aromatic' (Gottwald 1958), when dry. Fresh bark and sapwood of Honduras rosewood (D. ste• vensonii) are said to "have a distinctive odor, suggesting stored apples" (Record & Hess 1943), but the dry material stored over a long period oftime in the RBHw collec• tion is odourless. Density - With a density of 0.94 (early-formed wood) to 1.12-1.23 g/cm3 (mature wood), D. congestiflora is an extremely hard and heavy timber, comparable to 'coco• bolo', 'funera' and 'Honduras rosewood'. Within the Central American species of Dal• bergia studied only those of the D. tucuruensis group stand out on account of their considerably lower density (Table O.

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Vessel characters - Vessel and intervessel pit morphology is similar for all studied taxa. Quantitative differences occur in pit diameter as well as vessel diameter and frequency. Vertical pit diameter is around 5-7 /ll11 in D. congestiflora and D. funera, 8 -10 /ll11 in the other species. The smallest and most frequent vessels are found in D. funera, intermediate values in D. congestiflora, while the remaining species are char• acterised by commonly very large and few vessels (Fig. 2b-f, Table 1). Axial parenchyma (Fig. 2b-f) - Distribution and amount show distinctly different patterns. Banded parenchyma is the dominant type in D. congestiflora and D. funera. In all species comprising the 'cocobolo' group, axial parenchyma is predominantly apotracheal diffuse-in-aggregates or in narrow, uniseriate bands forming an incon• spicuous reticulate pattern with the fine rays. Dalbergia stevensonii and the D. tucuruensis group show a less explicit distribution pattern with paratracheal (sparse to vasicentric to aliform and confluent) and some apotracheal parenchyma (small groups and/or discontinuous, anastomosing bands) combined in varying proportions. In addi• tion, all species possess narrow, more or less conspicuous marginal bands. Rays - Quantitative as well as qualitative ray features such as width, height, fre• quency, and cellular composition are very uniform in all species studied (see above description of D. congestiflora) and do not offer any secure means of differentiation except perhaps within the 'cocobolo' group: rays are predominantly uniseriate in D. retusa, D. hypoleuca and D. lineata, bi- and/ or triseriate in D. granadillo. Mineral inclusions - In all species / specimens prismatic crystals were observed in chambered, crystalliferous axial parenchyma cells (one crystal per chamber), most frequently in those of the bands delimiting growth ring boundaries. Prismatic crystals in marginal and submarginal ray cells were found exclusively in D. congestiflora and D·funera. Storied structure - In all studied species/specimens cells are arranged in regular horizontal series. As is common with Dalbergia, all rays and axial tissues are storied. The number of tiers is a constant (5-)6(-7) per axial mm with no significant differ• ences between species and specimens. Heartwood fluorescence - Corresponding tests with longwave ultraviolet light proved negative on freshly planed surfaces of all studied species and specimens. Shortwave ultraviolet light produced a faint yellowish-green fluorescence solely with D·funera. Colour (Table 1) and fluorescence of ethanol extract, extractive contents (Table 2) - Essentially, all ethanol extracts reproduce the heartwood colour variation. That of D. congestiflora is an intense violet, resembling the colour of an aqueous solution of potassium permanganate. Extract colours of the cocobolo group yield a variety of col• ours ranging from faint yellow to deep orange-brown to copper; those of the D. tucu• ruensis group vary from faint yellow to light pinkish brown. Extracts of D. stevensonii and D. funera are the least colour intensive with faint yellow to pinkish hues. Fluores• cence of ethanol extracts is rather weak, of greenish colour, and similar for all studied species and specimens, respectively. Generally, all observations on colour and fluores• cence correspond very well with those made by Quirk (personal comm. 1985) for Cen• tral American species of Dalbergia.

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Table 2. Extractives content of heartwood and sapwood specimens from selected Central American Dalbergia species (sapwood specimens in italics).

Species Specimen RBHw-No. Type of wood Extractives content (% dry matter)

D. congestiflora 18731 heartwood 29 D. congestiflora 18276 heartwood 30

D. granadillo 16326 heartwood 27 D. hypoleuca 13987 heartwood 13 D. hypoleuca 13987 sapwood 3

D. tucuruensis 18277 heartwood 14 D. tucuruensis 18277 sapwood 3 D. tucuruensis 18255 heartwood 17 D. palo-escrito 19765 heartwood 19

Extractives content was determined only for selected heartwood and sapwood speci• mens. The highest amount of extractives was found in specimens of D. congestifiora and D. granadillo (close to 30%). The lighter-coloured D. hypoleuca, D. tucuruensis and D. palo-escrito contain moderate amounts of 13% to 19%. For lack of adequate material D. funera and D. stevensonii were not included; yet extractives content is ex• pected to be moderate. Thin-layer chromatography - This test was not designed for an in-depth interpre• tation including identification and quantification of individual chemical compounds. Nevertheless, it allows a comparison between species with some interesting results (Fig. 3). For one, segregation of extractive constituents of the species studied produces basically similar running patterns. On the other hand, sufficient individuality is evi• dent for distinguishing between species or species groups on account of number and nature (position, colour, fluorescence) of segregated compounds (spots). The fully iden• tical patterns of D. granadillo and D. retusa (cocobolo) indicate a close relationship. The chromatogram of D. congestifiora is unique in showing the highest number (11) of individual compounds, among them two with an intense blue fluorescence. One of these spots is retained next to the starting line, a position unmatched by any of the other species' chromatograms.

With reference to wood structure and some physico-chemical features there is no doubt that the four 'camotillo' specimens (one vouchered, three commercial) assembled for this study are identical and might represent Dalbergia congestifiora, first described by Pittier (1922) in his treatise on Dalbergia of Mexico and Central America. Despite some variation of quantitative features, the wood structure readily conforms to the basic pattern observed in Dalbergia, characterised by diffuse-porous vessel distribu-

Downloaded from Brill.com10/06/2021 10:25:09AM via free access 338 IAWA Journal, Vol. 17 (3),1996 tion; simple perforations; intervessel pits alternate, of medium size and vestured; ves• sel-ray and vessel-parenchyma pits similar to intervessel pits; fibres libriform and non• septate; rays 1 to 3 cells wide, numerous and very low; rays and axial tissues storied; prismatic crystals common in chambered axial parenchyma cells; silica absent. The only previously published data on general, macroscopic and microscopic wood fea• tures of Dalbergia congestiflora (Barajas-Morales 1985; Barajas-Morales & Leon Gomez 1989) are, according to introductory notes in the latter paper, based on a single specimen collected at Chamala, Jalisco, Mexico, A comparison with the above de• scription reveals only slight differences from the above data in density (0.81 g/cm3 ) and quantitative characters such as average vessel diameter (71 /JIll) and frequency (22/mru2 ), intervessel pit diameter (5-9 /JIll), number of rays (7/mm). Parenchyma distribution, however, is described as "paratracheal scanty with tendency to aliform with short wings." Such a parenchyma pattern matches only that found in a very young tree (RBHw 18732). In conjunction with the lower density and smaller vessels this indicates that Barajas-Morales & Leon Gomez's description was based on a fairly young specimen rather than on mature wood. The most striking feature of D. congestiflora is the deeply violet and, upon expo• sure, remarkably stable heartwood colour which readily sets it apart from other Cen• tral American species of Dalbergia. Violet hues are also known from some other Dal• bergia species, among them the Brazilian 'kingwood' and 'pau violeta' (D. cearensis and D. violacea, see Burger 1979). In those timbers, however, violet is only one of sev• eral prevailing tones of an often irregularly striped heartwood (Record & Hess 1943), which tend to fade rapidly upon exposure.

Based on general similarity in wood structure, four more or less well defined groups can be distinguished among the Central American species of Dalbergia:

Dalbergia granadillo, D. hypoleuca, D. lineata and D. retusa These species agree in all aspects of wood structure except ray width (see above) and possess chemically identical heartwood extractives, though in different quantities. This assembly provides the 'cocobolo' of trade and had already been recognised as a group of closely related species by Record and Garrat (1923, including D. calycina). It is again suggested by Rudd (personal comm. 1985) as a distinct taxonomic group within neotropical Dalbergia, however excluding D. calycina and "probably includ• ing D. cuscatlanica and D. pacifica."

Dalbergia tucuruensis (= D. cubilquitzensis) and D. palo-escrito Dalbergia tucuruensis, though long known in Guatemala as an excellent technical timber, is a relative newcomer to the international market. It is traded as 'granadillo rojo' and primarily used for decorative veneers. Dalbergia palo-escrito, first described by Rzedowski and Guridi (1988), appears to be endemic to a short stretch of the Sierra Madre Oriental in central Mexico; the wood is used locally mainly for backs of guitars and fine furniture. The wood of both taxa is identical in all structural and physico• chemical aspects and differs from the remaining Central American Dalbergia species

Downloaded from Brill.com10/06/2021 10:25:09AM via free access Richter, Krause & Muche - Wood of Dalbergia congestiflora 339 mainly in parenchyma distribution and by its remarkably low density and characteris• tically light coloured heartwood with frequent dark-brown streaks (for wood descrip• tion of D. palo-escrito see Rzedowski & Guridi 1988). These authors point out that most vouchered specimens of D. palo-escrito had formerly been identified as D. tu• curuensis, a "probably closely related species" known from moist tropical forests in Guatemala, Belize, Nicaragua and southern Mexico (Chiapas).

Dalbergia congestiflora and D. funera Both species are apparently very rare and have never been commercialised beyond occasional use by local craftsmen. They possess a similar wood anatomy which differs from the above taxa in several aspects such as the predominantly banded parenchyma, smaller and more frequent vessels, smaller intervessel pits and the presence of pris• matic crytals in rays. Heartwood colour (deep violet brown for D. congestiflora, light yellowish brown for D.funera) and extractives composition of the two species, how• ever, are quite distinct and also differ significantly from the species groups listed above (Table 1, Fig. 3).

Dalbergia stevensonii This species is somewhat difficult to place in any of the above groups. On account of its axial parenchyma distribution it would seem closest to the D. tucuruensis group with which it also shares its origin from moist tropical forests on the Atlantic side of Central America (Belize and eastern parts of the Yucatan Peninsula) than to any other of the above groups. However, its high density and heartwood colour set it readily apart from D. tucuruensis and D. palo-escrito.

As there have not been any recent taxonomic treatments of Dalbergia in Mexico and Central America since Pittier (1922), it is difficult to relate the above findings to any classification at the subgeneric level. Rudd (personal comm. 1985) provisionally rec• ognised four groups as follows: 1. D. retusa, D. hypoleuca, D. granadillo, D. lineata, and, probably, D. cuscatlanica and D. pacifica. 2. D. tucuruensis (incl. D. cubilquitzensis), D. melanocardium, D. glome rata, D. conges• tiflora, D. calderonii (including D.funera), and, probably, D. stevensonii. 3. D. calycina, D. intibucana. 4. D. brownei. The first group includes all species comprising the cocobolo of trade whose very simi• lar, if not identical, wood structure and extractives' chemistry suggests a very close relationship as pointed out before and confirmed by the present study. The two addi• tional species mentioned by Rudd are not commercialised. Neither reference speci• mens nor records of any wood anatomical description were available for comparison. The second group comprises all other commercial Dalbergia species from Central America plus some non-commercial species including D. congestiflora (D. palo-escrito would have to be included here but the description was not yet published at the time).

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No differentiation within this group can be inferred except from the term 'probably' preceding D, stevensonii, designating this species as possibly distinct from the others, The separation of the other two wood anatomically distinct taxa defined above (D, tucuruensislD. palo-escrito and D. congestifloraiD. funera) is not reflected in this sec• ond of Rudd's species groups. The third and fourth group consist of taxa not included in this study for lack of commercial significance and/ or specimens. Judging from two vouchered specimens in the RBHw collection apparently collected from very small plants or branches (no heartwood), D. brownei shares the characteristically banded parenchyma with D. congestiflora and D.funera, but may be distinct on account of its exclusively uniseriate rays. This specific feature, however, is not conclusive when found in specimens repre• senting juvenile or branch wood. In adult wood of the same species rays may be pre• dominantly 2 to 3 cells wide (see description of D. congestiflora).

CONCLUSIONS

Wood of Dalbergia congestiflora, a species apparently endemic to Mexico, yields a very heavy timber with an outstanding appearance due to the deep violet colour and subtle surface variegation. The wood is easily differentiated from other commercial species of Dalbergia native to Central America on account of its specific wood struc• ture and heartwood extractives composition. In combination with exomorphic features these criteria offer a better means for the circumscription of species and species groups within Dalbergia than may be inferred from the presently available taxonomic treat• ments. Future attempts at a natural classification of Dalbergia should therefore also employ wood structure and, particularly, the chemistry of heartwood extractives as tools for detecting and defining relationships within this genus.

Key to commercial Central American species of Dalbergia 1) - Axial parenchma predominantly in continuous tangential bands, intervessel pit diameter 5-7 j.IIIl, crystals in ray cells present...... 2) - Axial parenchyma otherwise, intervessel pit diameter 8-10 /lffi, crystals absent in ray cells...... 3) 2) - Heartwood yellow to olive brown; vessels 1O-15/mm2 ...... D.funera - Heartwood deep violet, variegated; vessels 5-1O/mm2 ...... D. congestiflora 3) - Axial parenchyma predominantly apotracheal diffuse-in-aggregates, occasionally in uni• seriate tangential lines (,reticulate'), heartwood dark orange to reddish brown, commonly with dark streaks ...... 4) - Axial parenchyma predominantly paratracheal vasicentric to aliform and confluent. 5) 4) - Rays predominantly uniseriate ...... D. retusa, D. lineata, D. hypoleuca - Rays predominantly 2- or 3-seriate ...... D. granadillo 5) - Heartwood light to dark leatherbrown with dark streaks, density ~ 0.80 g/cm3, largest vessels up to 450 j.IIIl in diameter ...... D. tucuruensis, D. palo-escrito - Heartwood light to dark pinkish brown, density ± 1.00 g/ cm 3, largest vessels up to 350 m in diameter ...... D. stevensonii

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REFERENCES

Baas, P. 1986. Terminology of imperforate tracheary elements - in defence of libriform fibres with minutely bordered pits. IAWA Bull. n.s. 7: 82-86. Barajas-Morales, J. 1985. Wood structural differences between trees of two tropical forests in Mexico. IAWA Bull. n.s. 6: 355-364. Barajas-Morales, 1. & C. Le6n G6mez. 1989. Anatornia de maderas de Mexico: especies de una selva baja caducifolia. Publicaciones especiales No.1, Instituto de Biologia, Universidad Nacional Aut6noma de Mexico. Berti Nardi, R. & M. L. Edlmann Abbate 1992. Legnami tropicali importati in Italia - Anatomia e identificazione. Vol. II, America latina. Instituto per 1a Ricerca suI Legno, Firenze. Burger, L.M. 1979. Estudo anat6mico do xilema secundario de 7 especies nativas do genero Dalbergia, Leguminosae-Faboideae. Disserta<;:ao, Dept. Engenharia Florestal, Setor de Ciencias Agnirias. Curitiba, Parana, Brasil. Gottwald, H. 1958. Handelsh61zer. Ferdinand Holzmann Verlag, Hamburg. IAWA Committee. 1981. Standard list of characters suitable for computerized hardwood iden• tification (eds. R.B. Miller & P. Baas). IAWA Bull. n.s. 2: 99-145. IAWA Committee. 1989. IAWA list of microscopic features for hardwood identification (eds. E.A. Wheeler, P. Baas & P.E. Gasson). IAWA Bull. n.s. 10: 219-332. Mabberley, D.J. 1987. The plant-book. Cambridge University Press, Cambridge. Pittier, H. 1922. Dalbergias of Mexico. J. Wash. Acad. Sci. 12,3: 57-64. Record, S.J. & G.A. Garrat. 1923. Cocobo10. Yale University, School of Forestry, Bull. No.8. Yale University Press, New Haven. Record, S. J. & R.W. Hess. 1943. Timbers of the New World. Yale University Press, New Haven. Rzedowski, J. & L.I.Guridi-Gomez. 1988. EI palo escrito, arbol de madera preciosa- una nueva especie mexicana de Da1bergia (Leguminosae, Papilionoideae). Acta Bot. Mexicana 4: 1-8. Weis, A. 1981. Orientierende Versuche zur Pilzresistenz des Splintholzes von schweren Holzem. Diplomarbeit, Fachbereich Biologie, UniversiUit Hamburg.

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