Use of wood anatomy to identify poisonous plants : Charcoal of Spirostachys africana

Spirostachys africana Sond. (tamboti/tambotie) is a woodland tree that is often found near water. It has a poisonous and purgative latex. The archaeological site of Sibudu, a rock shelter in KwaZulu-Natal, has evidence, from well-preserved charcoal and seeds, of past environments and wood use from approximately 77–38 thousand years ago (ka). As their uses and environmental indicators are different, it is critical to confidently distinguish among the three anatomically similar woods of the Euphorbiaceae: Spirostachys africana, Sclerocroton integerrimus and Shirakiopsis elliptica. A detailed anatomical study of reference and archaeological charcoal shows that xylem vessel width increases proportionally as vessel frequency decreases, from Spirostachys africana, Sclerocroton integerrimus to Shirakiopsis elliptica. Crystals of calcium oxalate are present in ray cells of Spirostachys africana, whereas silica bodies are present in ray cells of Sclerocroton integerrimus and Shirakiopsis elliptica. Using these features, the presence of Spirostachys africana was confirmed amongst hearth charcoal of the Spotty Camel layer, with an age of approximately 58 ka and of the Mottled Deposit occupational layer, with an age of approximately 49 ka. The presence of this charcoal, collected from ancient fireplaces or sieved from surrounding sediments, implies that people at Sibudu understood and used this poisonous tree to their advantage. We are encouraged in this view by the presence of many Cryptocarya woodii leaves found on the surface of 77-ka sedge bedding at Sibudu (Wadley L et al., Science. 2011;334:1388–1391). Cryptocarya woodii has insecticidal and larvacidal properties and members of the Laurel family are well known for their medicinal properties.


Sibudu
Sibudu is situated on the uThongathi River, KwaZulu-Natal.3][4][5][6] Some of the evidence for the behaviour of the anatomically modern people who visited and lived at Sibudu includes stone tools, ochre, bone, perforated seashells and hearths [7][8][9][10][11][12][13][14][15] , as well as evidence for the making and use of compound adhesives 16 , and circumstantial evidence for snares 17 and bows and arrows 18 .[21][22][23][24][25][26][27] The relevance of identifying Spirostachys africana The presence of charcoal at Sibudu implies that people who visited and occupied the site burned wood. 2,4,5irostachys africana charcoal was tentatively identified from Sibudu in a previous study. 20,21Nowadays, the wood from this tree is not used as fuel for cooking because the smoke and fumes are poisonous. 28People who live in a particular environment for long periods develop knowledge about local resources 2,14,25,29 and the Spirostachys africana wood was almost certainly recognised for its toxic properties and utilised by ancient hunter-gatherers 14 .Therefore a secure identification of the archaeological charcoal is necessary in order to interpret behavioural strategies in the past.
Sclerocroton integerrimus wood anatomy is similar to that of Spirostachys africana. 1,20,30Both were recorded as Spirostachys/Sapium in the scanning electron microscopy (SEM) study of charcoal from Sibudu, 20,21 so it is important to try to distinguish between the two taxa.Shirakiopsis elliptica wood anatomy is also similar. 1,31As it was not in the original charcoal reference collection for Sibudu, 20 new fresh material was gathered, charred and studied.

Anthracology
Archaeological charcoal is identified by means of wood anatomy [32][33][34][35] to describe palaeoenvironments and palaeoclimate and to develop an understanding of past wood use [36][37][38] .Anatomical features of living or fresh woods, listed by the International Association of Wood Anatomists, accessed on InsideWood, an online database 39 , can assist with charcoal identification 34,35,40 but charred reference material is more useful [41][42][43] .Woody taxa have been identified from charcoal assemblages from many sites elsewhere in southern Africa; a few examples are Diepkloof Rock Shelter 44 and Elands Bay Cave in the Western Cape 45 and from sites in Lesotho 46,47 .

Habits, habitats and uses of the three woods
Spirostachys africana is a medium-sized, hardwood, deciduous tree, 10-18 m tall, and grows in woodland and valley bushveld.Often found in dense stands; in warm, dry areas along rivers and drainage lines; in poorly drained brackish and clay soils; or near underground water, tambotie is distributed from KwaZulu-Natal to Tanzania. 48Sclerocroton integerrimus is a small-to medium-sized, hardwood, deciduous tree, 2-10 m tall, and grows in coastal thicket, on forest margins and in wooded grassland. 48Shirakiopsis elliptica is a medium to tall, softwood, deciduous tree, 12-20 m tall.It grows in wooded ravines and is common at the canopy edge of evergreen forests and as a canopy tree in swamp forests. 48The timber of the three trees is similar. 49e bark, wood, stems and leaves of Spirostachys africana contain poisonous milky latex 28 which is used as a purgative in small doses 50 .This fish and arrow poison causes conjunctivitis when in contact with the eyes 28 and urticaria and blistering when in contact with the skin 28 .][52][53][54][55] Cytotoxic and genotoxic activities have been reported. 28,52e cytotoxins in latex are phorbol esters, which are terpenoids. 28,54pirostachys africana is classified as an extremely hazardous Class IA cellular poison according to the four toxicity classes recognised by the World Health Organization.This measure of poisoning is based on an LD 50 determination in rats, that is, less than 5 mg of plant material ingested per kilogram body mass killed 50% of the population. 28Poisons kill in minute amounts, toxins are less toxic than poisons and toxicants are toxic in high concentrations only. 50) Phorbol esters affect mucous membranes in the skin and the alimentary tract. 28[52][53][54][55] Spirostachys africana wood is hard and heavy with a beautiful close grain coppery brown colour, impervious to insect attack and weathering. 48hen burned, the wood gives off a sweet odour, which can cause headaches, nausea and diarrhoea. 28,55The Venda use Spirostachys africana smoke to fumigate their huts against wood-boring and other insects (Anonymous reviewer, 2014, written communication of personal observation, July 03).
Sclerocroton integerrimus has clear latex which is suspected of being poisonous and is used as a mouthwash to relieve toothache and coughs. 56Fruit is used to make ink and as a source of tannin.Fallen fruit and leaves are eaten by antelope and stock animals. 48irakiopsis elliptica is considered very poisonous and is used as a drastic purgative in West Africa. 57The rough bark has sparse, scattered depressions and clear latex.Bark latex is added to arrow poison, ouabain, from the East African Acokanthera schimperi and is used as bird lime and for body markings. 57Acokanthera oppositifolia (Bushman's poison), distributed along eastern and northern parts of South Africa, is amongst the Acokanthera species which are known to be sources of extremely toxic arrow poisons. 28Various parts of the Shirakiopsis elliptica tree are used in folk medicine in Africa, in dermatology and gastroenterology, particularly as an anthelminthic. 57

Wood anatomy
A detailed study of the wood anatomy of Spirostachys africana, Sclerocroton integerrimus and Shirakiopsis elliptica has been done to distinguish among these taxa and to clearly identify Spirostachys africana in charcoal from Sibudu.Modern reference material was collected specifically for this project, charred in a furnace and supplemented with data from InsideWood and the literature.As outlined below, the three woods share similar features but there are several useful distinguishing characteristics.

Comparative reference collection
A wood sample of Spirostachys africana from a Southern African Forestry Department woodblock stored in the Department of Archaeology, University of the Witwatersrand, was carbonised and studied as a reference of anatomical features (SJL 103; Table 1, Figure 1a-c).Inferred archaeological Spirostachys africana charcoal from Ndondondwane Iron Age site 58 in KwaZulu-Natal was used as intermediate reference material (NDO; Table 1, Figure 1d).Reference wood samples and voucher herbarium specimens of Sclerocroton integerrimus (SJL 88, Figure 1e) and Shirakiopsis elliptica (SJL 67, Figure 1f) were identified by local botanists and were collected ex hort in Durban and on a farm near Port Edward, KwaZulu-Natal (coordinates 31.04615°S,30.16886°E) for a study of anatomical features (Table 1).

Methods
Reference woodblocks were charred in a LENTON 0861 muffle furnace (Lenton, Hope, UK) for 3.5 h at 350 °C at the Palaeosciences Centre, University of the Witwatersrand.2][43] Charcoal blocks were viewed from three planes by means of stereomicroscopy (Olympus SZX16, Münster, Germany) and reflective and polarised light microscopy (Olympus BX51) at magnifications of 100x, 200x and 500x.Characteristic anatomy was digitally photographed using Olympus Stream Essentials ® image analysis software with extended focal image capability.Anatomical features according to the International Association of Wood Anatomists' list 35,39 were recorded for the comparative reference material and archaeological specimens.Identifications were also confirmed against published reference material. 1,32,33,39,49

Useful distinguishing features
Prismatic crystals occur in Spirostachys africana ray and parenchyma cells, whereas silica bodies are absent in this species. 1,30,59Silica bodies occur in Sclerocroton integerrimus 2,60 and Shirakiopsis elliptica 1,31 ray cells, whereas crystals are absent from ray cells 40 .Crystals are occasionally visible in the parenchyma cells of Sclerocroton and Shirakiopsis. 2ismatic crystals are not common in wood anatomy and their occurrence may be sporadic. 35Features such as crystals and silica bodies are therefore useful attributes and are listed as an anatomical feature when commonly observed.Prismatic crystals are solitary, rhombohedral or octahedral crystals of calcium oxalate which are birefringent (produce a rainbow effect) under polarised light 35 and appear shiny in charcoal specimens.
Silica bodies are spheroidal or irregularly shaped particles of silicon dioxide which are non-birefringent (do not produce a rainbow effect) under polarised light 35 and appear opaque.Silica is present in ray cells in African Sapium species in aggregates, which often fill the entire cell lumen, or as grains or small dark dots in Asian Sapium species such as

Attributes common to Spirostachys, Sclerocroton and Shirakiopsis
Vessels are commonly arranged in long, radial multiples (>4).Perforation plates are simple.Inter-vessel pits are alternate and polygonal; medium (8-10 µm) in Spirostachys africana 1,30,49 , medium to large (8-10 µm to 11-16 µm) in Sclerocroton integerrimus 60 and large (11-16 µm) in Shirakiopsis elliptica 31 .Vessel-ray pits are bordered and similar to inter-vessel pits in size and shape in Spirostachys africana and Shirakiopsis elliptica; rounded or angular, with much reduced borders, in Sclerocroton integerrimus.Fibres are non-septate, with simple to minutely bordered pits.Fibres are short in Spirostachys africana; in Sclerocroton integerrimus, they are medium length and regularly arranged.Shirakiopsis elliptica fibre length varies from short to long (Figure 1).Diffuse parenchyma occurs in Spirostachys africana.Parenchyma which is diffuse-in-aggregate (SJL 103, Figure 1a), or in narrow bands or lines which are up to three cells wide, may be observed as a variation. 1,30,49arenchyma which is diffuse or diffuse-in-aggregate is difficult to see.In Sclerocroton integerrimus parenchyma is diffuse-in-aggregate and/ or there are narrow bands or lines up to three cells wide. 60Shirakiopsis elliptica parenchyma is diffuse and/or diffuse-in-aggregate, with the variation of occasionally occurring in narrow bands or lines up to three cells wide. 31Axial parenchyma strand length is either 4 or 8 cells per parenchyma strand in all three woody taxa.
Rays are exclusively uniseriate, commonly heterocellular, with procumbent, square and upright cells mixed throughout the ray (SJL88, Figure 1e), although this pattern varies within and between the three woody taxa (Table 1; SJL 103, Figures 1a-c; NDO, Figure 1d).Shirakiopsis elliptica reference charcoal ray cells are upright and square (SJL 67, Figure 1f).Very long rays occasionally occur in Shirakiopsis elliptica where two rays meet end to end, and are visible in both reference material (SJL 67) and archaeological material (SPCA B4c 45). 1,31,40ys are frequent, with up to 12 observed per millimetre.Laticifers -thin, radial tubes carrying latex which occasionally occur in Euphorbiaceae wood -were absent from the charcoal examined. 1,35

Distinguishing attributes of reference material
The charcoal of the three species differs in vessel size and frequency as well as in the presence or absence of crystals or silica bodies in ray cells.The differences in vessel size and pattern among the wood of the three species are recorded in a photographic study of endgrain woodblocks of Euphorbiaceae. 49irostachys africana has several to many, small to medium vessels in long radial lines. 1,30,49Charcoal reference, SJL 103, (Figure 1) and interpreted reference material, NDO, vessels are narrow (30-50 µm), at a frequency of between 40-100 vessels per mm 2 (an average of 80/mm 2 ) and vessels are arranged in long radial lines (radial multiples > 4).The prismatic crystals in ray cells are birefringent, appearing shiny under reflected polarised light.Shape may vary in different material, from clearly rhombic in the archaeological specimen -which is an interpreted reference for Spirostachys africana (NDO in Figure 1d) -to irregular but shiny in the modern wood forestry block reference material (SJL 103 in Figure 1b and 1c).Crystals are visible in the SEM images recorded by Allott 20 .Silica bodies are absent from ray cells.The vessel inclusions are either resin 1 or gum 30 .Resin occurs in the heartwood. 1Similar comparative images of Spirostachys africana have been recorded by Allott 20 , Ilic 32 and Kromhout 33 .
Sclerocroton integerrimus has few, medium to large vessels in radial lines. 1,60Charcoal reference material, SJL 88, vessels are narrower than 100 µm, at a frequency of 20-40 vessels per mm 2 , and are arranged in short radial lines of two to four vessels.The silica bodies are nonbirefringent and opaque under polarised light (SJL 88, Figure 1e). 35he silica bodies present in ray cells are spheroidal, irregularly shaped particles 35 arranged in aggregates which often fill the entire cell lumen 40 .These silica bodies are visible in the SEM images recorded by Allott 20 .Prismatic crystals are absent from ray cells.Sapium luzonicum. 40The arrangement (aggregated, irregularly shaped or globular) or surface (smooth or verrucose) may be diagnostic in certain groups and needs to be recorded in a description. 35

Results and discussion
Figure 1 illustrates reference charcoal of the three taxa.Figure 1d, Spirostachys africana (NDO), is of archaeological charcoal and is therefore an interpreted identification.Figure 2 illustrates the identified archaeological charcoal from Sibudu.Table 1 summarises the charcoal anatomy of the modern reference and archaeological material.Table 2 lists the most useful diagnostic features for identifying the three species, the environmental conditions required by the trees and the medicinal and other uses for their wood.

Timber
The hard, heavy wood has contrasting light sap wood and dark heartwood, with an attractive lustre when polished and has therefore been used as a replacement for sandalwood.It is used in furniture, for staves, beads and bangles and in construction as rafters.The sawdust is poisonous, as is the wood if burnt for fuel, causing conjunctivitis, nausea and food poisoning. 28,55e hard, durable wood is used as timber for general purposes, in construction and for furniture. 56e tough, soft, light, white wood is used to make instruments, burnt as firewood and charcoal, but not used as rafters when used in construction as it is susceptible to insects. 57

Phytochemistry and uses
Phorbol esters (terpenoids) classify latex in bark, wood, stems and leaves as an extremely hazardous, Class 1a, cellular poison (LD 50 =5 mg/kg). 28,50,61Isolated terpenoids have antibacterial properties. 28very drastic purgative, the bark and milky latex are used to treat alimentary tract infections.Latex is used to treat tooth decay and eye infections.Used as fish and arrow poison, latex causes conjunctivitis, or a severe contact dermatitis.Bark is used for skin ailments, and headaches.The fragrant woodblocks are an insect repellent. 62Smoke is inhaled for treatment of respiratory infections. 28,55xic tetracyclic triterpenic cucurbitacins have been extracted from root bark of Sclerocroton cornutus from West and Central Africa. 56spected of being poisonous, the clear latex is used as an antiseptic against toothache and coughs.The fruits were formerly used to make a black ink and are used for tanning. 56nnins and alkaloids have been extracted from the whole plant.Bark extracts have moderate antimicrobial activity against Campylobacter jejuni which causes food poisoning. 57nsidered very poisonous and a very drastic purgative, the clear latex is added to arrow poison and used as bird lime. 57irakiopsis elliptica has very few, large to very large vessels in radial lines. 1,31Charcoal reference material, SJL 67, (Figure 1f) vessels are wider than 100 µm, at a frequency of fewer than 10 vessels per mm 2 , and are arranged in short radial lines.Silica bodies occur as grains or small dark dots in Asian Sapium species. 41In our reference material, the silica bodies are inconspicuous, prismatic crystals are absent from ray cells with occasional crystals observed in the parenchyma and tyloses commonly occurring in vessels. 1,31irostachys and Sclerocroton archaeological charcoal Spirostachys africana was identified in charcoal from Sibudu from MOD square C6a and from SPCA squares B4b and D5c.Specimens MOD C6a 39 and SPCA 62 have as many as 110 vessels per mm 2 , small (20-30 µm) to medium (50-100 µm) in size and arranged in radial multiples >4 (long radial lines); rays are uniseriate, frequent and heterocellular, with mixed procumbent, square, upright cells.Prismatic crystals occur in ray cells and shine under polarised light (Figure 2a-c).

Summary of the characteristic diagnostic features of each species
The detailed anatomical study of reference material enables the identification of these taxa based on the occurrence of crystals in Spirostachys africana and silica bodies in Sclerocroton integerrimus and Shirakiopsis elliptica ray cells 1 as well as on vessel size classes and frequency of vessels.These diagnostic characteristics are compared in Table 2.
The vessel size of Spirostachys, Sclerocroton and Shirakiopsis increases proportionally as vessel frequency decreases, from Spirostachys africana, with the smallest and most numerous vessels, to Sclerocroton integerrimus, then to Shirakiopsis elliptica with the largest and fewest vessels.

A comparison of anatomical features
No clear differentiation in anatomical features among these three taxa under investigation could be found, thus necessitating this study.There is some variation in vessel width and frequency, ray cell type, the absence or presence of tyloses in vessels, of laticifers in rays and of gum or resin deposits in vessels among different published accounts. 1,30,31,33,49,59lative abundance of crystals may vary.As wood is inherently variable, some features are well defined in some samples, but poorly defined or absent in other samples of the same species. 35There are no quantitative criteria for 'common' in the list of the International Association of Wood Anatomists.Comments on relative frequency are therefore added to descriptions. 35e crystals of calcium oxalate are birefringent under polarised light; however, some cell walls, especially lignified cell walls, are also birefringent (Anonymous reviewer, 2014, personal observation, written communication, July 03 tangential longitudinal section in which the cell walls are cut away.The outline of these crystals is visible, differentiating these crystals from ray cell walls in the radial longitudinal section.Under non-polarised light, the crystals in the inferred reference material match those seen in SJL 103 and those usually seen in wood 35 and charcoal 44 .The crystals seen in archaeological specimens of Spirostachys africana match those found in reference material SJL 103 ray cells observed in radial and tangential longitudinal sections at high magnification. The Spirostachys africana crystals are magnified to 500x the original size and they are clearly visible.In SEM studies of charcoal, energy dispersive x-ray spectrometry analysis capabilities may be used to distinguish between crystals of calcium oxalate and silica, such as the crystals found in Searsia undulata (Namaqua kuni-bush), Cassine peragua (spoon-wood) and Gymnosporia buxifolia (spike-thorn) from archaeological charcoal at Diepkloof Rock Shelter. 44e variation in anatomical features between the charcoal and fresh wood or between charcoal made from modern wood and archaeological charcoal are because of the natural variation occurring in biological material affected by the sample origin (twig or trunk) or habitat. 49uantitative variation may be a result of the shrinkage and distortion which occurs during the formation of charcoal. 36,38 have supplemented the charcoal wood anatomy descriptions with those from fresh woods from the InsideWood database as more detail usually is visible in fresh wood.Comparative sizes rather than measurements are used in anthracology because the anatomy may be distorted by shrinkage, vitrification, diagenesis, and fragmentation and powdering. 36,38,41

Conclusion
The charcoal anatomy of Spirostachys africana, Sclerocroton integerrimus and Shirakiopsis elliptica enables these species to be distinguished by vessel arrangement, size and frequency, as well as by the presence or absence of crystals or silica bodies in ray cells.
Spirostachys africana has narrow, frequent vessels; prismatic crystals are present in ray cells.Sclerocroton integerrimus has wider, less frequent vessels.Of the three species under comparison, Shirakiopsis elliptica has the widest and least frequent vessels.Silica bodies are present in ray cells of Sclerocroton integerrimus and in Shirakiopsis elliptica as small grains and dots while prismatic crystals are absent from ray cells.The silica bodies of Sclerocroton integerrimus are aggregates of irregularly shaped silicon dioxide particles which often fill the entire cell lumen and appear opaque under polarised light.The silica bodies of Shirakiopsis elliptica appear as grains or small, dark dots.
Spirostachys africana was identified amongst hearth charcoal of the SPCA layer in squares B4b and D5c, with an age of approximately 58 ka; and in charcoal of the MOD layer in square C6a, with an age of approximately 49 ka.This find confirmed the use of Spirostachys africana wood at Sibudu rock shelter.Sclerocroton integerrimus charcoal occurred in SPCA in squares B4b, B4c and D5a and in MOD in square E3d.Shirakiopsis elliptica charcoal was found in SPCA B4c and in MOD in square C6a.

Sclerocroton integerrimus, Shirakiopsis elliptica and poisonous
Spirostachys africana wood was deliberately burned by people at Sibudu who utilised natural resources.Sclerocroton integerrimus timber is a hard, heavy, durable wood.Shirakiopsis elliptica timber is soft, light, and suitable for making implements.Spirostachys africana wood is a hard, durable wood, with poisonous properties.
Many of the present day uses of these woods were not applicable during the Middle Stone Age, but these species may have been selected for making wooden implements and for firewood.Spirostachys africana wood is a skin irritant and it seems unlikely that this wood would have been worked by hand to make implements.Nor does it seem likely that the poisonous wood was used for domestic fires to cook food.It seems more likely that Spirostachys was deliberately selected for its toxic or insecticidal properties, perhaps so that its smoke would fumigate insects from the camp in Sibudu.

Figure 1 :
Figure 1: Diagnostic characteristics of charcoal reference material: (a-c) Spirostachys africana (SJL 103), (d) Spirostachys africana (NDO), (e) Sclerocroton integerrimus (SJL 88) and (f) Shirakiopsis elliptica (SJL 67).(a) In transverse section, Spirostachys africana has many small vessels (V) in long lines.Vessels are occasionally in pairs.The shiny cell contents may be resin 2 or gum 30 .These fibres (F) are thin-walled and regular.(b) The radial longitudinal section has crystals labelled (C) in the ray cells, which shine under polarised light.Ray cells (R) are mixed; the procumbent cells are as high as the square cells and occasionally there are upright cells in the margins.The rays are low.(c) The tangential longitudinal section has frequent, uniseriate rays.The prismatic crystals of calcium oxalate in ray cells which distinguish Spirostachys shine under polarised light.Vessels with alternate inter-vessel pits occur and the vessel walls are birefringent under polarised light.The insert shows these ray crystals at a lower magnification.(d) Inferred Spirostachys africana reference material from Ndondondwane, KwaZulu-Natal (NDO) has prismatic, rhombic, crystals in the ray cells which shine under non-polarised light, in radial longitudinal section.(e) In Sclerocroton integerrimus reference material, SJL 88, there are silica bodies labelled (S) in the ray cells.These are spheroidal or irregularly shaped particles which are opaque under polarised light.The ray cells are heterocellular, mixed procumbent, square and upright in radial longitudinal section.The cell walls of the vessels, rays and fibres are birefringent in polarised light.(f) In Shirakiopsis elliptica reference material, SJL 67, the silica bodies (S) in ray cells are granular, dark spots.Rays are heterocellular with upright and square cells seen in radial longitudinal section.These inter-vessel pits are alternate.

Figure 2 :
Figure 2: Diagnostic characteristics of archaeological charcoal: (a-c) Spirostachys africana, (d) Shirakiopsis elliptica and (e,f) Sclerocroton integerrimus.(a) In Spirostachys africana, SPCA B4b 62, there are prismatic crystals (C) in the procumbent ray cells (R), under non-polarised light.(b) These appear shiny under polarised light in radial longitudinal section, matching those of the Spirostachys africana SJL 103 reference material.The vessel (V), fibre (F) and ray cell (R) walls are also birefringent under polarised light.(c) In Spirostachys africana, SPCA D5c 51, tangential longitudinal section, the ray cell walls are cut away and the crystals underneath are present and shiny, matching those of the Spirostachys africana SJL 103 reference material when magnified 500x.(d) In Shirakiopsis elliptica archaeological material, MOD C6a 46, silica bodies (S) are present as grains and dots in ray cells and appear opaque under both polarised and non-polarised light.Rays are heterocellular, with mixed upright, square and procumbent cells, in radial longitudinal section.(e) In Sclerocroton integerrimus archaeological charcoal, SPCA B4b 66, the silica bodies in the ray cells are spheroidal or irregularly shaped and opaque in non-polarised light in radial longitudinal section and in both polarised (f) and nonpolarised light in tangential longitudinal section.

Table 2 :
Comparing the wood anatomy, environment and uses of Spirostachys, Sclerocroton and Shirakiopsis (Euphorbiaceae)