IAWA Bulletin n.s., Vol. 9 (1), 1988: 75-87 WOOD FLUORESCENCE OF INDIGENOUS SOUTH AFRICAN TREES by Stephanie T. Dyer South African Forestry Research Institute, P.O. Box 727, Pretoria, 0001, South Africa Summary The fluorescence characteristics of South study of growth rings, the detection of ligni­ African hardwoods and their extracts were fication and the identification of diseased studied to determine their value in wood iden­ wood (Vodrazka 1929; Radley & Grant tification. Heartwood specimens and water 1948). Vodrazka (l.c.) remarked on the use­ and ethanol extracts of a1together 179 species fulness of wood fluorescence in rnacro- and representing 108 genera and 46 farnilies were microscopic studies using three examples, exarnined in longwave ultraviolet light. Ad­ Robinia pseudoacacia, Ailanthus glandulosa ditional tests were conducted for the presence and Rhus typhina. He studied heartwood of Aluminium natural saponins. The findings fluorescence in addition to fluorescence in of this research correspond with the current water, a1cohol and acetone extracts. An addi­ knowledge on wood fluorescence. The fami­ tional 40 wood species are listed by him as lies Leguminosae, Rutaceae and Anacardia­ being fluorescent. These include the genera ceae showed positive fluorescence for the Rhus, Acacia, Swartzia and Erythrophlewn. majority of their species. Platylophus trifolia­ Miller and Baas (1981) incorporated the fluo­ tus is the only indigenous species with a pos­ rescence of heartwood and its extracts in the itive reaction to the test for Aluminium. The IAWA 'Standard list of characters suitable froth test for natural saponins in wood has for computerized hardwood identification. ' variable results, restricting its significance in The aim of this study, which was initiated wood identification. These results show that in 1985, was to assess the presence of UV fluorescence is a useful characteristic in wood fluorescence in South African woods with the identification and may be applied as a rapid view to using the results for separating close­ and easy test to verify certain identifications. ly related species should they show differen­ Key words: Heartwood fluorescence, wood ces in fluorescence. The results obtained will identification, longwave ultraviolet light, be compared with existing data on wood flu­ Aluminium, froth test, saponins, South orescence and then be added to the list of African hardwoods, extract colours. characters used in the identification of hard­ wood species. Introdudion The incorporation of the results into a The use of ultraviolet light to study the local and possibly international data base is fluorescence characteristics of wood was envisaged. started many years aga when Goppelsröder studied the fluorescence of extracts of Java­ Materials and Methods nese woods in 1867 (Vodrazka 1929). The wood specimens tested are represen­ Longwave ultraviolet radiation has a range tative of the collection of indigenous timbers from 260 to 400 nm, and the best wave1ength of the South African Forestry Research Insti­ for the study of wood fluorescence is approx­ tute. Altogether 852 specimens representing imately 365 nm (Panshin & De Zeeuw 1980). 108 genera and 179 species were tested. Wood fluorescence has been used for a wide Where possible, five or more replicates of range of applications. These include the dis­ each species were tested, but in a number of tinction of sapwood from heartwood, the cases only a single specimen was available. Downloaded from Brill.com09/26/2021 03:43:30PM via free access 76 IAWA Bulletin n.s., VoI. 9 (1),1988 All tests were carried out according to the ed for approximately one minute, and the ex­ methods prescribed by Miller (1981), with tract colour scored as colourless, red, brown, minor modifications. In the recording of the yellow, reddish-brown, yellowish-brown or results, the recommendations of Miller were none of these as in Miller (1981). Some dif­ followed (Table 1). If 0 to 20% of the sam­ ferences in opinion occurred when extract pIes tested were positive, the taxon was re­ colours were recorded and a second opinion corded as being negative. If21 to 80% ofthe had to be considered in some cases. A possi­ sampIes were positive, the taxon was record­ ble solution to these problems would be the ed as variable and if 81 to 100% of the sam­ use of a standardised colour chart. It was also pIes tested positive, the taxon was recorded noted that the colour faded in time and it was as positive. therefore important to record this immedi­ Heartwood fluorescence was determined ately after heating. by removing a strip approximately 5 mm thick from the end surface of each specimen Ethanol extract fluorescence with a saw and studying the freshly exposed The method for this test was similar to surface under longwave UV light. The spec­ that for water extract fluorescence, except imens were recorded as either fluorescent that 95% ethanol was used instead of water. (colour given) or not fluorescent (-). Only The scoring was the same as for the test for sampIes which exhibited adefinite yellow, water extract fluorescence. green, purple, orange or blue fluorescence were recorded as being fluorescent. Dull blue Ethanol extract c%ur and dull green reactions were scored not The same method as that for water extract fluorescent, as these reactions may be due to colour was used. reflections of the UV light. Chrome Azurol-S test/or Aluminium Froth test to determine the presence 0/ na­ A 0.5% solution of chrome azurol-s was tural saponins prepared in sodium acetate and distilled wa­ Approximately 2.5 ml of sawdust was re­ ter. Two drops of reagent were applied to the moved from each sampie, placed in a vial freshly exposed end grain of each sampie. and covered with 10 ml of distilled water, Positive reactions developed a bright blue buffered at a pH of 6.8, shaken vigorously colour in a matter of minutes. for 10 to 15 seconds, and immediately view­ ed under UV light to score for water extract Results and Discussion fluorescence. One minute after shaking, the The shortage of relevant literature on wood froth (if present) formed by the water extract fluorescence made initial interpretation of was scored as folIows: Positive (+) if froth the results of the South African hardwoods was still present and covered the surface of difficult. Fortunately the Forest Products Lab­ the solution, negative (-) if all froth had oratory of the United States Department of disappeared, and variable (V) if froth was Agriculture was prepared to compare these present, but only around the edge of the test results with the results of the corresponding tube and did not cover the entire surface. genera in their collection. The results listed below have been found to compare favour­ Water extract fluorescence ably with existing results. Immediately after shaking the extract for the froth test, the solution was examined un­ Heartwood fluorescence der UV light. Extracts which fluoresce ex­ Of the 46 families tested for heartwood hibit definite blue, green, yellow and purple fluorescence. 10 were positive in that some colours. Some extracts showed positive fluo­ orall the genera fluoresced. The fluorescence rescence but the colours were weaker. colours were yellow, green, yellowish-green, blue, and orange and the colours varied in Water extract colour intensity. Most heartwoods fluoresced with a After the froth test, the extracts were boil- yellow or yellowish-green colour. Downloaded from Brill.com09/26/2021 03:43:30PM via free access Dyer - Fluorescence of South African woods 77 Table 1. Fluorescence characteristics of indigenous South African hardwoods . ., "Cl 8 l'l ., I:i ., u ., [;l ~ I:i .€ ., ... 1 ., [;l .u a> .s 0 Ul > Ul [;l :t;ä ~ § ., ., ., os ~ 0 " .s'~ p. ... ..:: "8 ~ 0 ~'': ..:: .., utbD 'Gl os ..," "8.., u ~ ..:: u ]~ Ul " 8.~ ~ "Cl .. I ~ ..,~ . '5 0 ~ ., "~~ Ul ., ~., ~., 1 ... '0 '0 ., ., ..,~ .s~ ... ... I:i 1! tä os § .~ -:5 os .s .s .~ Species s lil., o bD -:5 -:5 ;: z" ~ ~ ~ ~ ~ r.< r.< 0& Anacardiaceae Harpephyllum caffrum 5 V brown yellowish- brown Sclerocarya birrea 8 V yellowish- yellowish- brown brown Protorhus longifolia 4 green + brown bright green brown Rhus chirindensis 8 green + reddish- red brown Rhu8 gueinzii 4 green + reddish- green red brown Rhus lancea 7 green + reddish- green red brown Apocynaceae Gonioma kamassi 8 green bluish- yellow bright yellow green yellowish- green Rauvolfia caffra 5 V brown yellowish- brown Aquifoliaoeae Ilex mitis 8 + yellowish- yellow brown Araliaceae Cussonia .picata 8 + yellowish- colourless brown Schefflera umbellifera 3 ligh blue lightblue colourless light blue colourless Asteraoeae Brachylaena discolor 6 V yellow light blue yellow ssp. discolor Brachylaena discolar 3 V yellow light blue yellow ssp. transvaalensis Brachylaena glabra 1 yellow light blue yellow Brachylaena huillensis 4 V yellow blue reddish- brown Tarchonanthus galpinii 2 V yellowish- yellowish- brown brown Balanitaceae Balanites maughamii 2 + yellow bright blue yellow Bignoniaceae Kigelia africana 2 V yellowish- yellowish- brown brown Bombacaceae Adansonia digitata 2 + yellow grey Boraginaceae Cordia caffra 5 + reddish- bright brown brown purpIe Downloaded from Brill.com09/26/2021 03:43:30PM via free access 78 IAWA Bulletin n.s., Vol. 9 (1),1988 (Table 1 continued) 0> 0> u u <: 0> <: 0> ""21 0> 1Jl .. .~>' ]: ~ 0> ... 21 0> 1Jl ... .u 4) 1Jl +r! ::s § 6 .. :> 0> 0> ';'~ 0 .s:;:l '" ... ::s~ <;:: "8 'a 0 ~ .~ <;:: '0 ..., Clfg\, ::s ·S :> ..., ..., u ~ <;:: u u" ] ~ 8.~ os ::s • .... .. 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