IAWA Journal, Vol. 26 (I), 2005: 79-92

WOOD ANATOMY OF ()

R. D. Heady 1 & P. D. Evans2

SUMMARY

The anatomy of the Western Australian species Actinostrobus are­ narius (Cupressaceae) is described for the first time and its features are compared with those of the two other species in the genus: A. acuminatus and A. pyramidalis. Mature heartwood in A. arenarius is light-brown in colour and has an air-dry density of0.56 g/cm3. Average tracheid length is 4.3 mm. A very prominent warty layer, with individual warts commonly greater than one micron in height and large enough to be visible to light microscopy, lines the inner walls of tracheids. Callitroid thickening is commonly present in narrow (latewood) tracheids, but is absent from wide ones (earlywood). Axial parenchyma cells with dark-red resinous inc1usions are tangentially zonate in earlywood. Bordered pitting in early­ wood and latewood is uniseriate. Pit borders are circular and there is a raised torus. Average ray height is low. Cross-field pitting is cupressoid and the number of pits per cross field ranges from two to five, with a mean of 3.1. Average ray heights, ray frequencies, ray volumes, and numbers of pits present in cross fields are higher in A. arenarius than in A. pyra­ midalis, thus supporting the c1assification of A. arenarius as aseparate species within Actinostrobus. Veins of distorted xylem cells, similar in appearance to 'frost rings' occur sporadically in the sterns of a11 three species. If such rings are confined to Actinostrobus, then the combination of a very prominent warty layer, and the common occurrence of frost rings could provide a means of separating Actinostrobus from . Validation of this scheme requires further research to determine if such rings commonly occur in Callitris. Key words: , A. acuminatus, A. pyramidalis, wood anatomy, callitroid thickening, warty layer, frost ring.

INTRODUCTION

Trees belonging to the genus Actinostrobus are small multi-stemmed endemie to the south-western corner ofWesternAustralia. The contemporary 'Flora of ' (Hill 1998) lists three species in the genus: A. acuminatus, A. arenarius and A. pyrami­ dalis. The most-recently recognised species, A. arenarius, was formerly taxonomically inc1uded with A. pyramidalis, but was dec1ared a species in its own right by Gardner

I) ANU Electron Microscopy Unit, RSBS, and School ofResources, Environment and Society (SRES). The Australian National University, Canberra, ACT 0200, Australia. 2) Department of Wood Science, University of British Columbia, Vancouver, Canada.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 80 IAWA Journal, Vol. 26 (1), 2005

(1964) mainly on the basis of its cones, "the fertile scales of which are larger than those of A. pyramidalis and have erect and somewhat acute, not in-curved apices." The wood anatomy of A. arenarius has not previously been described. Descriptions of the wood anatomy of A. acuminatus and A. pyramidalis have been carried out by Baker and Smith (1910), Patton (1927), Peirce (1937), Prince (1938), Phillips (1948), and Greguss (1955). All of these accounts, however, were based on very 1imited numbers of wood sampies, mainly non-vouchered, or on twig or branch-wood specimens. For example, Patton (1927) had no sampies of A. acuminatus and does not state whether his A. pyramidalis sampies were stern or branch-wood. Peirce (1937) used one sampie each of A. acuminatus and A. pyramidalis. Prince (1938) gives no indica­ tion of his sampling procedure. Phillips (1948) had access only to twig material of A. acuminatus and had no specimens of A. pyramidalis. Greguss (1955) used "a specimen corning from a branch 6 years old", had "no material for comparative purposes" and ad­ mits that his description "requires to be supplemented" because of sampling limitations. This may explain why reports of callitroid thickening within the genus are contradic­ tory. Callitroid thickening is reported to be present in A. acuminatus (Kleeberg 1885; Phillips 1948; Barefoot & Hankins 1982) whereas Baker and Smith (1910), Peirce (1937), Prince (1938), and Greguss (1955) make no mention of its presence in their studies, and Patton (1927) reported it to be "absent". There is clearly a need for a com­ prehensive examination of the wood anatomy of Actinostrobus including that of the undescribed species, A. arenarius, in order to resolve this discrepancy. More importantly a complete description of the wood anatomy of Actinostrobus would complement re­ cent molecular phylogenetic studies of the ofthe Cupressaceae (Gadek et al. 2000; Pye et al. 2003). These studies have confirmed the close association between Actinostrobus and Callitris (Gadek et al. 2000), and have suggested a particularly close relationship between Actinostrobus and the Western Australian Callitris species, C. drummondii (Pye et al. 2003). The aims of this study were: 1) to describe the wood anatomy of A. arenarius for the first time and comment on the taxonomic significance of findings; 2) to compare the wood anatomy of A. acuminatus, A. arenarius and A. pyramidalis, and to determine whether anatornical differences between the three species (if any) support the classi­ fication of A. arenarius as aseparate species; and 3) to fully describe certain features of the wood anatomy of A. acuminatus and A. pyramidalis that have received little at­ tention in previous studies.

MATERIALS AND METHODS

Wood sampies were obtained by incremental coring of growing wild in their natural habitat in flat, sandy scrub, with no over-storey, some occurring as remnant vegetation on roadside verges (Fig. 1). Seven core sampies, each taken from a different , were obtained for each of the three Actinostrobus species. In addition, several billet sections of the trunk wood of each species were obtained for assessment of wood colour, den­ sity, and appearance of growth rings. Figure 2 shows the approximate geographical locations of the sampled trees.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy 0/ Actinostrobus (Cupressaceae) 81

Fig. 1. Actinostrobus arenarius growing on a roadside verge near Badgingarra, . The white guide-post is approximately one metre high.

Specimens were observed using light microscopy (LM) and scanning electron mi­ croscopy (SEM). Light microscope sections (approximately 20-50 !olm thick) were rnanually cut from water-soaked wood sampies using a single-edged razor blade. Sec­ tions were observed unstained or stained with safranin (to stain lignin, cherry-red), fast green (to stain cellulose green), or Sudan 4 (to stain fats and resins red) (lane 1970). AZeiss Axioskop microscope with halo­ gen illumination was used to examine specimens. Digital images of selected x =A. orelloril/S wood features were captured using a 0= A. aCl/millow.\ 'Spot' digital camera system (Diagnos­ p =A. pyramid(lfis lics Instruments Inc.). Plane surfaces for SEM were cut, prepared, and viewed by SEM as desöribed previously (Heady & Evans 2000).

Fig. 2. Map showing the approximate geo­ graphicallocations of the sampled trees.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 82 IAWA Journal, Vol. 26 (1), 2005

The densities of irregularly shaped stem-wood samples were determined using an Archimedian method (ASTM 1983) after soxhlet extraction of samples with acetone for 24 hours. Tracheid length was measured optically using the method of Ladell (1959). Ray heights, ray frequencies, ray volumes, and wart sizes were determined from pre­ recorded SEM images on a Macintosh G3 computer using an image analysis program (NIH Image, National Institute of Health, USA) (Evans et al. 1994). Mean ray heights, frequencies, and volumes were calculated from measurements of all rays present in one square millimetre areas of tangential longitudinal surfaces (TLS) in each of the seven samples for each species, (300-400 rays per species). The number of cross-field pits occurring in two cross fields in 10 rays within each of the seven samples was also quantified for each species. Analysis of variance was used to determine the significance of differences in ray height and cross-field pit numbers between species. To ensure that the data conformed to the assumptions of analysis of variance, i.e. normality with constant variance, diagnostic checks were carried out on the data before final analysis. As a result of such checks ray height data was transformed into naturallogarithms and analysed as logarithm of ray height. Statistical computation was carried out using Gen­ stat (Program 5, Release 3.1 Lawes Rothamstead Experimental Station, UK). Results are presented graphically and aleast significant bar can be used to explore statistically significant (p < 0.05) differences between individual species means.

RESULTS

Physical and macroscopic characteristics of the wood ofActinostrobus arenarius Longitudinal surfaces of dry, freshly-cut heartwood are light-brown, barely discem­ ible from the dark cream colour of the sapwood. There are no colour streaks. Growth rings on smooth transverse surfaces are discemible to the naked eye. Persistent branch traces extending through 5-15 growth rings were noted. Wood does not have a distinct odour or taste. Its air-dry density is 0.56 g/cm3 and its basic density is 0.53 g/cm3.

Microscopic characteristics ofthe wood ofActinostrobus arenarius Boundaries of growth rings are 'distinct' due to an abrupt change in the radial diam­ eter oftracheid lumina at the latewood-earlywood interface (Fig. 3). Latewood is 'incon­ spicuous' according to the definition of Phillips (1948) since it occupies less than one­ quarter of the width of the growth ring (Fig. 3). Earlywood tracheids are thin-walled and rectangular in outline in transverse section (TS). Average tracheid length is 4.3 mm. Transition from earlywood to latewood is 'abrupt' (Fig. 3). Resin canals are absent. Axial parenchyma cells, filled with a dark-red resinous substance, are common. The arrangement of parenchyma cells is tangentially zonate; tending to be grouped into lines parallel to growth-ring boundaries in the earlywood (Fig. 4). The trans verse walls ofaxial parenchyma cells are smooth (unpitted) and entire. Tracheid pitting on radial walls ofboth earlywood and latewood is uniseriate, rarely partially biseriate and opposite. Bordered pitting does not occur on tangential walls. Pit apertures are circular. A torus is present and is well defined, having a dense central area with a convex lens shape (Fig. 5). The torus is not scalloped, but there are (rare) occurrences of extensions to the torus.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy of Actinostrobus (Cupressaceae) 83

Fig. 3-6. Wood anatomy features of Actinostrobus arenarius. - 3: TS showing growth rings. - 4: LM image ofTS showing axial parenchyma (dark coloured) in earlywood dose to growth ring boundary. - 5: Bordered pit showing a well-defined, convex-Jens-shaped, torus. - 6: Callitroid thickening (arrows) present in narrow tracheids on the left and absent from wide tracheids on the right. - Scale bars in 3 & 4 = 200 !!m; in 5 =5 !!m; in 6 = 50 !!m.

Callitroid thickening is often present, but is always confined to narrow (Iatewood), rather than wide (earlywood) tracheids (Fig. 6). Two basic types of callitroid thickening occur. The most cornmon type consists of two bars, one on either side of the pit aperture, and with both bars extending completely across the radial wall of the tracheid from one side to the other. In the second type of callitroid thickening, two bars are present, but they extend only partially across the radial wall of the tracheid. A very prominent warty layer, with both large and small-sized warts, lines the inner walls of tracheids (Fig. 7-9). Individual warts are large enough to be visible to LM (Fig. 8). The large warts are tubular in shape with rounded tops (Fig. 9) and are greater than one micron in height. The largest wart measured during our studies was 1.69 f-tm in height and measured 0.64 f-tm across its base. Large warts commonly have small hemi­ spherical protrusions (nodules) on their surfaces (Fig. 9). Warts are, in general, discrete entities although pairs ofthe tallest warts are occasionally anastomosed (Fig. 9). Small hemispherical warts, approximately 20 nm in diameter, are interspersed between the larger ones. Organic deposits and helical thickenings in tracheids are absent.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 84 IAWA Journal, Vol. 26 (I), 2005

Fig. 7-9. The warty layer of Actinostrobus arenarius. - 7: TS showing very prominent warty layer lining the inner walls of tracheids. - 8: LM image of RLS showing warty layer. - 9: Sec­ ti on of tracheid wall viewed at 55° showing nodules (n) and anastomosed warts (a). - Scale bars in 7 & 8 = 10 11m; in 9 = 111m.

Ray height is low (Table 1). Rays are uniseriate (Fig. 10) and rarely partially biseri­ ate. Cross-field pitting is cupressoid (Fig. 11). The number of pits per cross field ranges from two to five, with a mean of 3.1 (Table 1). End walls and horizontal walls of ray parenchyma cells are smooth (Fig. 11). Callitroid thickening occurs on some cross-field pits, mainly in cross fields of the narrow (latewood), rather than the wide (earlywood) tracheids (Fig. 12). Ray tracheids and indentures are absent.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy 0/ Actinostrobus (Cupressaceae) 85

Table I. Wood anatomy characteristics far each of the three species of Actinostrobus.

Characteristics A. arenarius A. acuminatus A. pyramidalis

I Air-dry density 0.56 0.60 0.58 2 Basic density 0.53 0.56 0.54 3 Ray height 24 -108 - 287 23 - 104 - 364 22 - 84 - 220 4 Ray height 1- 5.6 - 15 1- 5.1- 18 1- 3.9 -11 5 Ray frequency 50.1 47.5 42.9 6 Ray volume 9.8 8.7 6.4 7 Pits present in cross field 2 - 3.1 - 5 1 - 2.6 - 5 1 - 2.4 - 4

Individual rows indicate the following: 1) Extracled air-dry density of wood in g/cm3. 2) Basic density of wood in g/cm3 3) Ray height in micrometres (~m). 4) Ray height in terms of number of cells. 5) Ray frequency in rays/mm2. 6) Ray volume (percent). 7) Number of pits per cross field (in earlywood). Minimums, means and maximums are represented using the format: [minimum - mean - maximum].

Fig. 10-13. Features of Actinostrobus arenarius. - 10: TLS showing rays. - 11: RLS showing a ray five cells in height with cupressoid cross-field pits and smooth cell walls. - 12: Callitroid thiekening (et) of cross-field pits. - 13: Trabecula (t) spanning three traeheids. - Scale bars in 10 =200 Ilm; in 11 & 13 = 20 Ilm; in 12 =50 Ilm.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 86 IAWA Journal, Vol. 26 (l), 2005

Fig. 14-19. Veins of distorted xylem cells in Actinostrobus arenarius. - 14: TS showing two veins (arrows) each measuring approximately 0.2 mm radially. - 15: TLS showing vein (right of centre) extending more than 1.5 mm axially. - 16: RLS showing vein (vertical, centre of image) intenupting adjoining ray (centre right). - 17: TS showing ray continuity intenupted by vein whereas ray continuity on the left beyond end of vein is normal. - 18: TLS showing warty layer present on inner walls of some cells of vein. - 19: RLS showing pits in cells of vein on the left (arrow) resembling the bordered pits in tracheids on the right. - Scale bars in 14 = 1 mrn; in 15 = 500 11m; in 16 & 18 = 100 11m; in 17 = 200 11m; in 19 = 50 11m.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy of Actinostrobus (Cupressaceae) 87

Fig. 20-25. Features of the wood of Actinostrobus acuminatus and A. pyramidalis. - 20 & 21. A. acuminatus. - 20: RLS showing (on the left) axial vein, callitroid thickening (at centre), and a single axial parenchyma cell (right of centre). - 21: Close-up view of warty layer. - 22-25. A. pyramidalis. - 22: TS viewed at 25° showing axial vein at the centre of image. Growth direc­ tion was from the bottom of the image towards the top. Note the disruption of orderliness of tracheid rows in the upper part of the image. - 23: Callitroid thickening in narrow tracheids on the left but absence of thickening from the wider tracheid (right of centre). - 24: Close-up view of warty layer. - 25: Pitting in cross fields of a ray showing 1, 2, 3, and 4 pits per cross field. - Scale bars in 20 & 22 = 50 !-lm; in 21 = 1 !-lm; in 23 & 25 = 20 !-lm; in 24 = 2 !-lm.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 88 IAWA Journal, Vol. 26 (1), 2005

There are occasional occurrences of trabeculae, wh ich are circular in cross section, 5-10 !Am in diameter, and are raised above the inner wall of the tracheid. The surfaces of trabecula are heavily warted (Fig. 13). Axial veins of distorted xylem cells (Fig. 14-19) occur sporadically throughout the stern. The radial and tangential widths of these veins range from approximately 0.05 to 0.2 mm and from 0.2 to 5 mm, respectively. All extend several mm axially (Fig. 15). The largest extended through more than 45 mm ofthe trunk. The veins are aligned parallel to the growth rings, but all of them extend through only a few degrees of the stern circumference. Veins occur at various radial positions within growth rings. In one sampie we noted that veins occurred in the same radial position within a particular growth ring at four different locations around the stern. Where veins occur, ray continu­ ity is usually interrupted (Fig. 16) or rays become laterally displaced (Fig. 17) and the arrangement of tracheids on the outer side of the stern becomes disorderly (Fig. 17). Tracheid arrangement and ray continuity beyond the tangential extremes of the veins is normal (Fig. 17). There is no 'false' growth ring associated with the vein. Individual cells in the veins tend to be wider than the surrounding tracheids (Fig. 18 & 19) and they often contain starch granules (Fig. 18). The thickness of the walls of cells in veins is similar to that of adjacent tracheids (Fig. 18). The inner surfaces of walls are usually smooth, but are occasionally warted (Fig. 18). Cells in veins often contain structures resembling the bordered pits in adjacent tracheids (Fig. 19) or the cross-field pits of rays.

Comparison ofthe wood anatomy ofthe three Actinostrobus species Callitroid thickening is present in all three species (Fig. 6,20 & 23), but is always confined to pits in narrow (latewood) rather than wide (earlywood) tracheids. No differ­ ence in the morphology or frequency of occurrence of callitroid thickening was found between species. The axial veins of distorted xylem cells described in A. arenarius (above) were also commonly found in A. acuminatus and A. pyramidalis (Fig. 20 & 22). Warts occur in a range of sizes in all three species, but the largest ones are always tubular in shape, have rounded tops, often have nodular protrusions on their surfaces and are sometimes anastomosed. Wart size and shape (Fig. 9, 21 & 24) is similar in all three species. Mean ray height was 84 pm (3.9 cells) in A. pyramidalis, 104 !Am (5.1 cells) in A. acuminatus and 108 !Am (5.6 cells). in A. arenarius (Table 1). The average number of pits present in cross fields, based on observation of 140 cross fields in each species, ranged from 2.4 in A. pyramidalis to 3.1 in A. arenarius (Table 1). Table 1 also shows the air-dry and basic density of the wood of each of the three species. Analysis of varlance of ray height and cross-field pit numbers in seven sampies ob­ tained from separate trees for each species revealed a statistically significant (p < 0.001) effect of species on ray height and numbers of cross-field pits. There was a statistically significant difference (p < 0.05) in the height of rays in A. arenarius and A. acuminatus compared to that of A. pyramidalis (Fig. 26). Differences in the numbers of pits present in the cross fields of individual species (Fig. 11 & 25) were also statistically significant (p < 0.05) (Fig. 27).

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy of Actinostrobus (Cupressaceae) 89

4.6 3.50 LSD I LSD I 4.5 5 3.00 ~ 2.50 _ 4.4 .n ~ E" .<: 2.00 Oll " ] 4.3 .s.." 1.50 e ""

4.0 0.00 A. aren A. acum A.pyrm A. aren A. acum A.pyrm Species Species Fig. 26. Variation in ray height for the three Fig. 27. Variation in number of pits present in Actinostrobus species. LSD = least significant cross-fields for the three Actinostrobus species. difference (p < 0.05). LSD = least significant difference (p < 0.05).

DISCUSSION

The wood anatomy of A. arenarius has been described for the first time. In general, A. arenarius possesses all the anatomical features common to Actinostrobus and expected of a member of the Cupressaceae. Ray height, ray frequency, ray volume and numbers of pits present in cross fields, however, are higher in A. arenarius than in A. pyramidalis (Table 1) thus providing support for Gardner's (1964) separation of A. pyramidalis into two species (A. arenarius and A. pyramidalis). In general the of all three species of Actinostrobus are anatomically similar, and no qualitative differences were found that would enable the woods of the three species to be separated. This study resolved the discrepancy that exists in the literature as to whether or not callitroid thickening occurs in all Actinostrobus species. Our findings c1early show that callitroid thickening is common throughout the genus. Callitroid thickening in Actino­ strobus was more common in narrow than in wide tracheids, and was also present in cross fields. The morphology of callitroid thickening in Actinostrobus was similar to that found in Callitris (Heady & Evans 2000), and this supports the c10se relationship between Actinostrobus and Callitris that has been strengthened by recent chemical ( biflavone) and molecular phylogenetic studies (Gadek & Quinn 1985; Gadek et al. 2000; Pye et al. 2003). There are two types of callitroid thickening in Actinostrobus. In one type there is a raised bar on either side of the pit aperture, both of which extend completely across the radial wall of the tracheid, while in the other type bars are present, but extend only partially across the radial wall. In our description of the anatomy of callitroid thickening in Callitris (Heady & Evans 2000) these two forms ofthickening were c1assified as Type 2 and Type 1, respectively. Callitroid thickening consisting of three or four bars, which were termed Types 3 and 4, respectively, for Callitris, were not observed in Actinostrobus. The veins of distorted xylem cells found in all three species of Actinostrobus here ap­ pear similar to the illustration in Baker and Smith (1910) that is annotated "traumatic

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 90 IAWA Journal, Vol. 26 (I), 2005 resin duct in A. pyramidalis." However, we do not consider these veins to be traumatic resin ducts. None of them were hollow or duct-like, and staining with Sudan 4 failed to indicate presence of resin. A photomicrograph of a transverse section of A. pyramidalis in Prince (1938) clearly shows a vein of large distorted cells orientated tangentially to a growth ring. The description that accompanies the photomicrograph suggests that Prince thought that the veins were composed of parenchyma cells as he wrote, "Growth rings bordered by thin late wood which tends to be obscured by scattering wood parenchyma." It is doubtful, however, whether the veins are composed of paren­ chyma in the normal sense as we observed that they possessed structures resembling bordered pits (Fig. 19). Therefore we have referred to the vein 's constituent cells simply as distorted xylem cells and further suggest below that they are a traumatic response to freezing. Evidence for the latter is that the veins closely resemble 'frost rings' in conifers as described by Glock (1951) and Glerum and Farrar (1966). In the regions in which Actinostrobus grows, air temperatures can go below freezing point at night and rise above 0 oe during the day. Thus it is possible that the veins are formed by temporary freezing of xylem mother cells in the cambium. On resumption of normal ray and tracheid formation after the period of abnormal cell development, surviving cambial initials are out of alignment, hence the displaced rays and misaligned tracheids on the outer side ofthe vein (Fig. 15). Displacement ofray alignment is reported to be a characteristic feature of frost rings in conifers (Harris 1934; Glerum & Farrar 1966). Banks (1982) has pointed out that susceptibility to cambial frost damage (in eucalypts) can be inftuenced by stern size: small sterns (as occur in Actinostrobus) have lower thermal mass than larger ones and are therefore more susceptible to damage. Banks (1982) has also postulated that trees can be expected to be frost hardy in spring and autumn as long as sufficiently low temperatures (around freezing) often occur and that once this temperature regime is broken by higher temperatures, then protection would be lost and frost damage would occur if freezing temperatures were to re-occur. This may explain the sporadic nature of the rings in Actinostrobus. We also suggest that freezing of the cambium in Actinostrobus occurs only in regions of the stern which are more exposed to frost due to the presence of narrow longitudinal cracks in the . This could explain why the veins usually extend for only short distances tangentially. According to Day and Peace (1934) lack of water can also cause abnormal growth of a type similar to that of a frost ring. However, since false growth rings were not found in the sterns, as might be expected due to the occurrence of drought, we think it more likely that the veins were caused by freezing of the vascular cambium. Individual warts in the warty layers lining the inner tracheid walls of all three Ac­ tinostrobus species were very large, making it possible to see warts using LM, which is not possible in almost all other genera. The largest warts were commonly greater than 1.3 11m in height (the maximum observed was 1.69 11m) and therefore they are the tallest warts of all conifer genera. They far exceed wart heights of 0.5 to 1 11m in "some [coniferous] species" reported by Liese (1965). This explains why the warty layers of A. pyramidalis were used by Wardrop et al. (1959) in an early study of the structure of warts in softwoods. Our finding of nodules on warts and the anastomosing of pairs of warts in Actinostrobus accords with similar findings for the morphology of warts in Callitris (Heady et al. 1994). Interestingly, the largest warts that we have

Downloaded from Brill.com09/23/2021 02:39:40PM via free access Heady & Evans - Wood anatomy of Actinostrobus (Cupressaceae) 91 observed previously were in the Western Australian Callitris species C. drummondii, where warts were commonly I flm high (maximum 1.2 flm) (Heady 1997). Recently, Pye et al. (2003) performed a molecular phylogenetic analysis of 18S-26S rDNA inter­ nal transcribed spacer region sequences in Callitris and allied genera, including Actino­ strobus, and found that C. drummondii and Actinostrobus were sufficiently similar to be grouped in a polytomy. The similarity in wart size in Actinostrobus and C. drum­ mondii supports this grouping. A possible explanation for the very large warts in Actinostobus lies in the hypothesis of Zimmermann (1983). He proposed that warts have the function of "catch(ing) bubbles of air which are present in freshly-thawed xylem water". Zimmermann (1983) points out that, if these bubbles are allowed to coalesce into larger-sized bubbles, they become more difficult to dissolve back into the water. Several small bubbles have a much larger surface area than a single large bubble of equivalent total volume and are therefore more readily reabsorbed. Large bubbles in xylem water represent a danger to the tree as they have the potential to cause blockages ofthe tracheids when they expand as xylem pressure drops and transpiration re-commences. Large knobbly warts could capture small bubbles and keep them from coalescing as Zimmermann has suggested. Since Ac­ tinostrobus possesses very large knobbly warts, is subject to temperatures below 0 °C, does not have thick bark or an over-storey to cushion it from extreme temperatures, Zimmermann 's hypothesis is particularly attractive. The common presence offrost rings in Actinostrobus is further evidence that freezing conditions are extreme. Descriptions of the wood anatomy of the Actinostrobus genus need updating to reflect some of the findings described here. In particular, the universal presence of callitroid thickening, the lack of distinct heartwood colour, the occurrence of 1-5 cross-field pits rather than 2-4 as listed by Phillips (1948), and the common presence of frost rings. Genera within the Cupressaceae are regarded as difficult to separate (Phillips 1948). The presence of callitroid thickening is widely used, however, to separate Callitris from other genera in the family including Actinostrobus. Dur finding that callitroid thickening is found in all three species of Actinostrobus limits the use of this feature as a means of separating Actinostrobus from Callitris. However, if the 'frost rings' that we have ob­ served here are confined to Actinostrobus, then their presence in combination with the very large warts in Actinostrobus could provide a means of separating wood of the genus Actinostrobus from that of Callitris, but validation of this scheme requires further re­ search to determine if 'frost rings' commonly occur in Callitris.

ACKNOWLEDGEMENTS The authors thank the Western AustraIian Departrnent of Conservation and Land Management (CALM), the Dandaragan Shire Office for permission to gather the wood sampies used in this research and an anonymous referee for helpful comments and in particular for referring us to recent molecular phy­ logenetic studies of the Cupressaceae.

REFERENCES ASTM. 1983. Standard test methods for specific gravity of wood and wood-base materials. An­ nual Book of ASTM Standards. Vol. 0409: 501-511.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access 92 IAWA Journal, Vol. 26 (I), 2005

Baker, RT. & H.G. Smith. 1910. AResearch on the Pines of Australia. W. Gullick, NSW Govt. Printer. Banks, J. C. G. 1982. The use of dendrochronology in the interpretation of the dynamics of the snow gum forest. PhD thesis. The Australian National University. Canberra. 246 pp. Barefoot, A. C. & F.w. Hankins. 1982. Identification of Modem and Tertiary Woods. Clarendon Press,Oxford. Day, W.R. & T.R Peace. 1934. The experimental production and the diagnosis of frost injury on forest trees. Oxford Forestry Mem. 16: 1-60. Evans, P.D., J.D.R Pirie, RB. Cunningham, c.F. Donnelly & KJ. Schmalzl. 1994. A quantita­ tive weathering study of wood surfaces modified by chromium VI and iron III compounds. Part 2. Image analysis of cell wall pit micro-checking. Holzforschung 48: 331-336. Gadek, P.A, D.L. Alpers, M.M. Heslewood & C.J. Quinn. 2000. Relationships within Cupres­ saceae sensu lato: a combined morphological and molecular approach. Amer. J. Bot. 87: 1044-1057. Gadek, P.A & c.J. Quinn. 1985. Biflavones of the Subfamily Cupressoideae, Cupressaceae. Phytochemistry. 24: 267-272. Gardner, C. A. 1964. Contributiones florae Australiae occidentalis 13. J. Roy. Soc. of Western Australia 47: 54. Glerum, C. & J. L. Farrar. 1966. Frost ring formation in the sterns of some coniferous species. Canad. J. Bot. 44: 879-886. Glock, W. S. 1951. Cambial frost injuries and multiple growth layers at Lubbock, Texas. Ecol­ ogy 32: 28-36. Greguss, P. 1955. Identification of living on the basis of xylotomy. Akademiai Kiad6, Budapest. Harris, H. A 1934. Frost ring formation in some winter-injured trees and . Amer. J. Bot. 21: 485-498. Heady, R D. 1997. The wood anatomy of Callitris Vent. (Cupressaceae): an SEM study. PhD thesis. The Australian National University. Canberra. 220 pp. Heady, R D., RB. Cunningham, C. F. Donnelly & P. D. Evans. 1994. Morphology of warts in the tracheids of pine (Callitris Vent.). IAWA J. 15: 265-281. Heady, R.D. & P.D. Evans. 2000. Callitroid (Callitrisoid) thickening in Callitris. IAWA J. 21: 293-319. Hili, K.D. 1998. Actinostrobus (Cupressaceae). In: A.E. Orchard (ed.), vol. 48. CSIRO Publishing, Melbourne. Jane, F. W. 1970. The Structure of Wood. Ed. 2. A&C Black, London. Kleeberg, A. 1885. Die Markstrahlen der Coniferen. Bot. Zeitung 43: 673-686. LadelI, 1. T. 1959. A new method of measuring tracheid length. Forestry 32: 124-125. Liese, W. 1965. The warty layer. In: W.A Cote (ed.), Cellular Ultrastructure ofWoody : 251-267. Syracuse University Press, New York. Patton, RT. 1927. Anatomy of Australian coniferous timbers. Proc. Roy. Soc. Vic. 40: 2-16. Peirce, A S. 1937. Systematic anatomy ofthe woods ofthe Cupressaceae. Trop. Woods 49: 5-21. PhilIips, E.W. 1. 1948. Identification of softwoods by their mieroscopic structure. Forest Products Research Bulletin 22. Her Majesty's Stationery Office, London. Prince, J. B. 1938. Stem-wood in the Gyrnnosperms. MSc thesis (For.), University ofNew Bruns­ wiek. 96 pp. Pye, M. G., P. A. Gadek & K J. Edwards. 2003. Divergence, diversity and species of the Austral­ asian Callitris (Cupressaceae) and allied genera: evidence from ITS sequence data. Austral. Syst. Bot. 16: 505-514. Wardrop, AB., W. Liese & G.W. Davies. 1959. The nature of the wart structure in conifer tra­ cheids. Holzforschung. 13: 115-120. Zimmerman, M. H. 1983. Xylem Structure and the Ascent of Sap. Springer-Verlag, New York.

Downloaded from Brill.com09/23/2021 02:39:40PM via free access