IAWA Journal, Vol. 19 (4),1998: 347-382

VESTURES IN WOODY PLANTS: A REVIEW by

Steven Jansen I, Erik Smets l & Pieter Baas2

SUMMARY

Vestures are defined as mostly branched or irregularly shaped pro­ tuberances on the inner surface of the secondary wall of wood incIud­ ing the surface of the wall lining the pit cavity. Based on a survey of literature, vestures in softwoods and hardwoods are discussed. Data on the chemical composition, ontogeny and possible functions are limited and partly contradictory. A preliminary list of dicotyledonous families is given in which vestures have been reported to occur. No general mor­ phological cIassification of the different types of vestures (and 'warts') has been accepted at present. The taxonomie and diagnostic value of this polyphyletic character can be considerable but should be evaluated for each individual taxonomie group. It is not cIear whether all types of vestures and warts are homologous; both structures remain poorly un­ derstood. Key words: Vestures, warts, wood anatomy, development, chemistry, sys­ tematics, hardwoods, softwoods.

INTRODUCTION

Progress in systematic botany depends substantially on a critical study of characters. Character research intends to define characters and character states on the basis of an accurate interpretation of character homology, which is an essential prerequisite for the reconstruction of phylogenetic relationships. The scoring of character states de­ pends on standardised methods of data accumulation and knowledge of the total range of structural variation as derived from comprehensive studies of a taxon. It is com­ mon knowledge that much morphologie al and anatomical work remains to be done in angiosperms to understand homologies for macromorphological, microscopic, and ultrastructural features. In addition to the interpretation of the homologous or homoplasious nature of fea­ tures, the definition of characters and character states poses many problems. Since the homologous nature of vestures and warts remains enigmatic, terminological ques­ tions also exist for vestures and warts. Vestures are minute protuberances on the sec­ ondary wall that are frequently associated with pits; vessel walls, perforations or heli­ cal thickenings can also be vestured (Bailey 1933; Butterfieid & Meylan 1980; Metcalfe & Chalk 1983; Carlquist 1988a). The term warts is commonly applied to minute, un-

1) Botanical Institute, Laboratory of Plant Systematics, K. U. Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Belgium. 2) Rijksherbarium /Hortus Botanicus, P. O. Box 9514, 2300 RA Leiden, The Netherlands.

Downloaded from Brill.com10/05/2021 09:04:58AM via free access 348 IAWA Journal, VoL 19 (4),1998 branched protuberances on the lumen surface oftracheids in gymnosperms (e.g., Liese & Johann 1954; Liese 1965), and on the wall ofvessel elements and fibres of dicoty­ ledons (Meylan & Butterfieid 1974; Parharn & Baird 1974; Ohtani 1979; Ohtani et al. 1983). In general vestures are branched and more complicated in shape than warts. Vestures are up to c. 1 f.Ull in diameter at their base and up to c. 3 f.Ull in height. Occasionally vestures with widely expanded branches reach up to c. 5 f.Ull in width (Ohtani & Ishida 1976). The size of warts usually ranges from 50 nm to 800 nm (Liese 1965; Ohtani & Fujikawa 1971; Ohtani 1979). Accordingly, the larger branched projections on the pit chamber wall or pit apert ure have been termed 'vestures', while the smaller unbranched ones on the inner surface of vessel wall have been termed 'warts' since they are almost similar in size and shape to warts on the tracheid wall of gymno­ sperms. Vestures in an intervessel pit and warts on the lumen surface of the vessel element are illustrated in Figure 1. Since warts and vestures are con­ sidered to be homologous on the basis of their morphology (contin­ uous transitions occur from the < larger branched protuberances to the smaller unbranched ones), on- warts togeny and chemical composition, the terms warts and warty layer have been considered redundant and replaced by vestures and ves- tured layer by Ohtani et al. (1984a). Although the similarity between -'1tJm warts and vestures was indicated earlier by other wood anatomists Fig. l. Schematic representation ofvestured intervessel (Cöte & Day 1962; Scurfield & pit and vestured vessel wall ('warts'). - P-M = pri­ Silva 1970; Scurfield et al. 1970; mary wall and middle lamella; S = secondary wall; Meylan & Butterfieid 1974; Ohtani Ch = pit chamber; Ca = pit canal; PA = pit aperture. & Ishida 1976; Van Vliet 1978), some authors retain a nomenclatural distinction, using 'vestures' for protuberances associated with pits in dicoty Iedons and 'warts' for protuberances on tracheid walls in gymnosperms or vessel or fibre walls in angiosperms (e. g., Castro 1988; Heady et a1. 1994; Dute et al. 1996). Ohtani (1985) for ex am pie uses the terms 'warts' and 'warty layer' for the description of the lumen and trabeculae surface of Abies sachalinensis. According to such terminology, the homology between both structures is only partial. It is obvious that changing of terminology causes difficulties and misunderstandings. Moreover, some authors use the term 'vesturing' to indicate both vestures and warts. In this paper 'vestures' are defined as mostly branched or irregularly shaped pro­ tuberances on the secondary inner wall including the walllayer lining the pit cavity. 'Vestured pits' are defined as pits having vestures while 'vestured walls' are walls with vestures.

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Since Bailey's (1932,1933) pioneer work on vestured pits and especially since the use of the scanning electron microscope in wood anatomical studies, there have been numerous reports on vestures. Most of these reports, however, only cover a limited number of taxa and do not deal with different aspects of the feature. During ongoing research on wood anatomical features of Rubiaceae, we learned more about the vari­ ation of vestures in this family. In order to gain general knowledge of this character literature for both hardwoods and softwoods was reviewed. Gregory's (1994) 'Bibli­ ography of Systematic Wood Anatomy of Dicotyledons' was very helpful in locating relevant papers. Apart from a short historical survey, this paper focuses on the follow­ ing aspects: chemical composition, pseudovestures, ontogeny, possible functions, rni­ cromorphology, useful models for classifying vesture types, distribution, and taxo­ nomic significance. Some parts of this paper were presented at the first biennial conference of the Systematics Association in Oxford (Jansen & Smets 1997).

HISTORICAL SURVEY

Since the late nineteenth century so-called cribriform pits have been known to occur in such families as Fabaceae and Myrtaceae. An early extended account of these struc­ tures was made by Jönsson (1892; Fig. 2). In a review of the eady work Record (1925) reported pits that exhibit a dotted appearance in members of 20 dicotyledonous families. The dots were thought to be minute perforations in the pit membrane, vary­ ing in number and distinctness, and appeared similar to the sieve-plate perforations in phloem. They were called 'sieve-like' or 'cribriform bordered pits' because it was as­ sumed that protoplasmic connections passed through the numerous small openings in the immature vessel members. Other records include Dutailly (1874), Heiden (1893), and Moll and Janssonius (1906-1936). • --•

Fig. 2. Drawings of 'sieve-like' or 'cribriform bordered pits' (from Jönsson 1892).

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Fig. 3. Light microscopicaI drawings ofvestured pits (from Bailey 1933).

Bailey (1932, 1933) demonstrated that the sieve-like appearance is not due to per­ forations of the pit membrane, but the result of minute outgrowths from the free sur­ face of the secondary cell wall (Fig. 3). In his c1assical and thorough light-micro­ scopic study Bailey (1933) exarnined 2660 species of 979 genera belonging to 152 families. He introduced the terms 'vestures' and 'vestured pit'. Small particles on the inside ofthe pit chamber of Pinus species were first reported by Kobayashi and U tsumi (1951) and by Liese (1951) using transmission electron microscopy. However, there are earlier reports of vessels and fibres having a 'granu­ lar appearance'; Müller (1890: 37) described trabeculae that show irregular, small, pock- or wart-like, shallow excrescences. Bailey (1933) also observed 'vestures' that occurred frequentlyon the inner surface of the secondary walls of vessels. Subse­ quently more papers revealed the presence of this structure in tracheids of gymno­ sperms (e.g., Liese & Johann 1954; Liese 1957, 1965; Wardrop & Davies 1962; Ohtani & Fujikawa 1971; Roig 1992; Heady et al. 1994). Because of the partic1e- or wart­ like appearance, the term 'warts' or 'warty layer' was applied. The introduction of the electron microscope in botanical research facilitated ultra­ structural research and provided a wealth of information resulting in a number of papers that shed more light on the origin and nature of warts (e.g., Cronshaw 1965; Scurfield & Silva 1969; Scurfield 1972; Baird et al. 1974a) and vestures (e.g., Schmid & Machado 1964; Schmid 1965; Scurfield & Silva 1970; Scurfield et al. 1970). While Cöte and Day (1962) suggested that warts and vestures are similar in nature and have a common origin, Schmid and Machado (1964) and Schmid (1965) stated that they are analogous structures because vestures are formed by the living cytoplasm while warts are composed of the dead protoplast. The distinction between vestures and warts has been maintained until their homologous nature was inferred on the basis of their morphology, chernical composition and common origin. Therefore, Ohtani et al. (1984a) proposed to abandon the terms 'warts' and 'warty layer' (see the Intro­ duction).

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CHEMICAL COMPOSITION

Most investigators who studied the chemical composition of vestures (e,g" CottS & Day 1962; Schmid 1965; Scurfield & Silva 1970; Baird et al. 1974b; Mori et al. 1980; Ohtani et al. 1984a) found that vestures are very resistant to chemical treatment and largely consist of lignin. It has been suggested, however, that the lignin is somewhat different from the lignin elsewhere in the cell wall because it appears to be more condensed. The other components of vestures are hemicellulose and a small quantity of pectin; vestures do not contain cellulose (Mori et al. 1980; Ohtani et al. 1984a). The interior of vestures appears homogeneous in TEM photographs and is more e1ec­ tron dense than the secondary wall. Vestures are weIl preserved in some archeological material apparently due to their high lignin concentration. Donaldson and Singh (1990) found that in wood of a c. 1000-years-old Polynesian canoe the secondary wall of fibres, vessels and paren­ chyma cells was extensive1y degraded but the vestures and compound midd1e lamella remained relatively intact. The warty 1ayer also exhibits partial resistance to wood destruction by fungal attack (Liese & Schmid 1962; Liese 1964, 1965). According to these authors, fungi of the brown rot group which hydrolyse only the polysaccharides of the cell wall do not appear to be able to digest the warts. In contrast, white rot and also some soft rot species can dissolve both elements. Engels and Brice (1985) showed that in barley straw the lignified cell walls covered with a warty layer are resistant to rumen micro-organisms. Simi1arly Singh et al. (1987,1993) reported that tunnelling bacteria can degrade all areas in Alstonia scholaris while vestures remained intact. The latter authors, however, conc1uded that the primary reason for the resistance of vestures to degradation by tunnelling bacteria is the much smaller size of vestures (maximum 0.3 j.llIl in width) compared with the size of the tunnelling bacteria and probably not the high lignin content. This should be tested using suitable wood substrates with vestures larger in diameter. The preservation of vestures in permineralised wood is somewhat more problem­ atic because it is often difficult to distinguish between actual structures and mineral deposits (e.g. Wheeler & Baas 1992). Unless fossil wood is extremely weIl preserved it ean be very difficult to establish the presence of vestures. Giraud and Lejal-Nicol (1989), for instance, eould not determine whether vestured pits are present or absent in Cassinium dongolense from the Cretaceous of northem Sudan. The accompanying illustrations ofvestured pits mentioned in descriptions offossil wood (e.g. Yang et al. 1992) usually do not permit an independent evaluation. The presence of vestures was carefully assessed with both LM and SEM in a weIl preserved Paleocene wood iden­ tified as Caesalpinioxylon moragjonesiae (Crawley 1988). Vestures are also 1ikely in an Eocene legurne from Wyoming (Wheeler & Baas 1992). Contrary to the observations above, Ranjani and Krishnamurthy (1988) and Castro (1991) reported that vestures of some members of the Leguminosae are free of lignin and are mainly composed of carboxylated polysaccharides such as pectins and hemicelluloses. Therefore the true chemie al eomposition seems not yet fully c1ari­ fied.

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PSEUDOVESTURES

Bailey (1933) was the first to warn against the misinterpretation of pits that appeared to be vestured by extraneous or coagulated material that accumulates in the pits of mature tracheary cells probably during post mortem changes or during the transfor­ mation of sapwood into heartwood. He noted that these deposits occur sporadically and are extremely irregular, contrary to true vestures that occur in every intervessel pit. He found that 13 families do have nonvestured pits, although they were reported by other investigators to have 'cribriform structures'. Similarly Baas (1972), Wheeler (1981), Gale (1982) and Quirk and Miller (1985) warn against interpreting various deposits in pit chambers as vestures. Pseudovestures are soluble in mild solvents and are not an integral part of the cell wall. Exley et al. (1974) and Gale (1982) found that sodium hypochlorite (20%) or commercial household bleach is effective in cleaning the wood of encrusting debris without degrading the vestures. Therefore, most investigators use this bleaching agent to remove deposits that might be called vestures.

ONTOGENY

As mentioned above, Bailey (1933) considered vestures to be outgrowths from the secondary wall. After studying living cells in differentiating xylem he found that vestures are formed by the cytoplasm during the later stages of the development of the tracheary elements. Later, several investigators, for instance Wardrop et al. (1963), confirmed the cell wall nature of vestures by electron microscopy. In the latest state of cell wall differentiation, the distribution of cytoplasmic com­ ponents (ER, dictyosomes, mitochondria and so on) is thought to determine the distri­ bution, shape and size of vestures (Cronshaw 1965; Wardrop 1965; Ohtani & Ishida 1976). Since the cytoplasmic components in maturing cells are sometimes more con­ centrated at the cell corners, and also in pits, the formation of vestures is predomi­ nantly localised in these areas (Liese 1965; Ohtani & Fujikawa 1971). Scurfield and Silva (1969, 1970) suggested that both vestures and warts are outgrowths from the inner secondary wall layer: they are regarded as "replica of the plasma membrane surface, the warts corresponding to invaginations in the latter through which wall materials were being actively secreted at the time the cell died" (Scurfield & Silva 1970: 319). Vestures are thereby considered as enlarged warts that conglomerate in the pits, and whether warts or vestures are formed is probably related to duration of protoplast activity in pits. This process is possibly enhanced by the occurrence of intercellular connections, or by pit canals that retard withdrawal or breakdown of the protoplast. An association of the deposition of vestures with invaginations in the plasma membrane was also mentioned by Mori et al. (1979). Ohtani and Ishida (1976) sug­ gested that the activity of the protoplast is prolonged in depressions in the cell wall which results in the formation of larger branched protuberances. The complexity of vestures is supposed to be associated with regions with a small radius of curvature such as pit apertures, pit chambers and pronounced helical thickenings (Ohtani et al. 1984a). These regions provide favourable sites where excess of wall material from

Downloaded from Brill.com10/05/2021 09:04:58AM via free access Jansen, Smets & Baas - Vestures in woody plants 353 the protoplast is deposited onto the secondary wall. Furthermore, Wu et al. (1988) noted that the development of vestures possibly depends on the morphology of pits: in Syzygium and Terminalia vestures occur in prominently bordered pits having smaller apertures but they are absent in the slightly bordered pits with larger apertures. Evidence for the deposition of vestures prior to the death of the protoplast was shown by Kucera et al. (1977). These authors reported the absence of vestures from the depression between the borders in vestured perforation plates and concluded that those vestures are deposited prior to the removal of the perforation partition by en­ zymes. Remarkably, observations of vestured pits in the diffuse-porous wood of Syzygium cumini by Nair (1989) revealed that vestures are absent in the vessels near the cambium, while pits located in vessels a few layers away from the cambium are completely filled with large and branched vestures. Nevertheless, the possibility that vestures in Syzygium develop subsequent to the lysis of cytoplasm (after differentia­ tion ofvessel members) as suggested by Nair (1989) seems very doubtful. Ohtani et al. (1984a) and Ohtani (1987) suggested that vestures are formed by an oversupply of wall material (lignin) from the protoplast at the final stage of the sec­ ondary cell wall formation. Since vestures are observed in vessel members, fibres, and also in the highly lignified parenchyma cells of several bamboo species, it was suggested that vestures develop at about the time cell wall lignification is completed (Parameswaran & Liese 1977). Moreover, the lignification process is supposed to be aprerequisite for the development of vestures. Vestures have never been observed in tension wood fibres with an inner nonlignified cell wall layer. The presence of vestures in lignified parenchyma cells of Lasianthus japonicus was found to be closely associ­ ated with reticulate thickenings (Ohtani 1986). The origin of the warty layer has been the subject of a number of investigations. Liese and Ledbetter (1963) and Liese (1965) were of the opinion that warts consist solely of components of dead protoplasmic material trapped between remnants of the plasmalemma and the tonoplast, and which is cemented to the wall in the last stages of cell differentiation. The dying protoplast thereby forms the warty layer. Wardrop and Davies (1962) suggested that warts consist in part of a 10calised cell wall thicken­ ing. Cronshaw (1965), however, showed that warts develop external to the plasma membrane and are deposited by the living cytoplasm (by dictyosome derived parti­ cles or by the endoplasmic reticulum) prior to its degeneration. Their formation is different from the formation of the primary or secondary wall. This view has been supported by Kutscha (1968), Scurfield and Silva (1970), Scurfield et al. (1970), Baird et al. (1974a), and Takiya et al. (1976). Warts found by Liese and Ledbetter (1963) in herbaceous plants such as Plantago were not regarded by Cronshaw (1965) as true warts because they are only degenerating organelles or lipid droplets. Unlike other investigators, Schmid and Machado (1964) and Schmid (1965) con­ cluded that vestures and warts are basically different in origin. According to them, vestures are formed after complete formation of the cell wall from substances that pass through the plasma membrane and attach to the .cell wall. These substances are possibly derived from the Golgi vesicles. The attached bodies differ from the cell wall by their nonfibrillar and amorphous content and their greater density. The warty

Downloaded from Brill.com10/05/2021 09:04:58AM via free access 354 IAWA Journal, Vol. 19 (4), 1998 layer, however, is formed by the plasma membrane and the tonoplast which occasion­ ally includes den se particles. When this warty layer covers vestures, 'warted vestures' are formed. Accordingly, vestures and warts are interpreted as two analogous struc­ tures: vestures originating first from the living cytoplasm, warts being remnants of the dead protoplast. However, other investigators concluded that warts cannot consist of cytoplasmic remains trapped between dried membranes (Cronshaw 1965; Kutscha 1968; Baird et al. 1974a). A membrane covering vestures was interpreted by Wardrop et al. (1963) as denatured membranous elements of the cytoplasm. Scurfield and Silva (1969, 1970) observed a membrane or celliining that generally covered the lumen of most vessels and tracheids whether vestures are present or not. Several questions remain unanswered. Why are vestures formed? Is the formation an unusual activity of the cytoplasm before it disappears or is the formation due to an oversupply of wall material (lignin)? To what extent is their formation different from that of the rest of the cell wall? More studies are needed to fully clarify the origin of vestures; there is no detailed modem study on the ontogeny and ultrastructure of vestures or warts.

HYPOTHESES ON POSSIBLE FUNCTIONS

Bailey (1933) concluded that vestured pits are confined to tracheary elements be­ cause in vessel-parenchyma pits, vestures are present in the pit chambers of the vessel but absent in the parenchymatous cell. Although the few reports of vestures in cells without a conducting function (Ohtani 1986, 1987; Hong & Killmann 1992) might suggest otherwise, vestures are thought to have a function closely associated with that of tracheary elements (Carlquist 1988a). Several authors suggested that diffusion of water, preservatives or pulping liquids, and adhesion and fixation of chemicals may be affected by the presence of vestured pits because pits are important structures in regulating the flow of liquid, and gases in the living tree (Liese 1965; Scurfield et al. 1970; Nair & Mohan Ram 1989). Zweypfenning (1978) suggested that vestures may decrease the risk of pit mem­ brane rupture caused by pressure drops between adjacent vessel elements after air emboli sm. Pit membrane aspiration in angiosperms may be safer in vestured pit-pairs because the vestures prevent excessive deflection of the pit membrane. However, littIe is known about the strength of pit membranes in angiosperms and we need to understand what pressure drops cause pit aspiration and rupturing of the pit mem­ brane in bordered pits. Vestured pits are not concentrated in taxa that have high nega­ tive pressure in their xylem (e.g., very tall trees or woody plants in xeric habitats). According to Zweypfenning's hypothesis, vestured pits could be of adaptive signifi­ cance in these plants. This hypothesis only explains the possible function of vestures associated with the pit chamber, involving the pit membrane. However, it does not explain the function of vestured walls. Carlquist (1982a) stated that functional hypotheses on vestures are difficult to verify because experimental data are lacking and hence little evidence other than systematic distribution and occurrence within cell types is available. Three alternative possible

Downloaded from Brill.com10/05/2021 09:04:58AM via free access Jansen, Smets & Baas - Vestures in woody plants 355 functions were proposed by Carlquist (1982a, 1988a) considering kind ofvessel wall sculpturing: (1) a lower resistance to water flow, (2) a mechanism for eliminating air cavitations in vessels and tracheids and restoring normal water columns, and (3) by means of an increased surface area and increased hydration a mechanism for with­ standing higher water tensions and preventing formation of air embolisms. Carlquist (1982a, 1982b) found most support for the last hypothesis by examples from system­ atic and ecological distribution of wall relief in conducting cells. It explains why conifers in both dry and cold climates would benefit from avestured wall facing the lumen in tracheids. Tracheids in Winteraceae show vestures only in those species inhabiting areas that experience frost (PateI1974; Carlquist 1988a, b, 1989a) but ves­ tures are absent in lowland tropical species (Carlquist 1983, 1988b, 1989a). Further­ more the presence ofvestured walls in latewood vessels but the absence in earlywood vessels (Fagus and Sassafras; Parharn & Baird 1974) and the variation in vesture size between earlywood and latewood (Ohtani & Fujikawa 1971; Verhoff & Knigge 1976) represent an interesting correlation because water tensions would be higher in latewood than in earlywood. A similar function has been suggested for functional aspects of helical sculpturing and other forms of relief within vessels (Carlquist 1982a, b; Dute et al. 1996). The presence of vestured pits in tracheoid cells of legurne seeds mayaiso be related to the development of high water tensions (Carlquist 1988). Baas et al. (1983) objected to Carlquist's (1982a, b) hypothesis that a bordered pit chamber already offers such a strong compartmentalisation that embolisms are most unlikely to be initiated here irrespective of presence or absence of vestures. More­ over, they found that Carlquist's interpretation seems in conflict with the frequently observed tendency that spiral thickenings are restricted or more pronounced in nar­ row vessels and vessel tips where bonding of water is least needed. Zimmermann (1983) concluded that it is not a simple matter to establish valid correlations between pit structure and habitat such as suggested by Zweypfenning (1978). He stressed that there are at least three additional factors which prevent tear­ ing of the pit membrane: the mechanical properties of the pit membrane, and the variation in depth and size of pits among species. According to hirn, scalariform per­ foration plates, spiral thickenings and vestures may have the function to catch bub­ bles when the ice in the vessels thaws at the end of the winter in cool temperate climates. Small bubbles will dissolve faster and this prevents coalescence of bubbles and vapour blockage. In recent decades plant anatomists have stressed the importance of ecological wood anatomy, e. g. Baas (1990), Baas and Schweingruber (1987), Barajas Morales (1985), Carlquist (1975a), Carlquist and Hoekman (1985), and Van der Graaff and Baas (1974). This resulted in critical comparisons between environmental variables and various wood anatomical characters. Heady et al. (1994) found that tracheids of Callitris showed vestures that could be categorised into two types. The species investigated from high rainfall environments show small and hemispherical vestures whereas large nodulated vestures occur in the species from dry habitats. Since large complex vestures provide more surface area than small hemispherical ones, these results were inter­ preted as a support for Carlquist's (1982a, b) hypothesis.

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One cannot exclude the possibility that vestures simply have no function and should be regarded as an oversupply of wall material from the protoplast. Anyway, we still walk on thin ice regarding the adaptative value of vestures. We should be cautious with our speculations because structural features may have more than one function and some functions may depend on several factors so that ecological correlations become complex.

MICROMORPHOLOGY AND CHARACTERISATION

Since the observations of Bailey (1933), several types of vestures have been pro­ posed on the basis of their micromorphology. Although Bailey (1933) did not list distinct types, his descriptions and diagrammatic representations suggest the follow­ ing categories: massive, coralloid, papillary and filamentous. Using electron micro­ scopy, Cöte and Day (1962) were the first to define different morphological catego­ ries of vestured pits. Because there was considerable variation within one species and since Bailey's categories ofvestures overlap, Cöte and Day (1962) as weIl as Schmid (1965) concluded that only two types can be easily recognised: branched and un­ branched vestures. Scurfield et al. (1970) believed that any classification of vestured pits on the basis of their morphology should include both their form in pit chambers and in pit aper­ tures. They suggested to classify vestured pits into four groups: filamentous, bead­ like, massive coralloid and massive foliate. However, intra- and interspecific varia­ tion in the structure of vestures was found to make the taxonomie significance of these vesture types of dubious value.

..-l).lm .../\.. /L Jl 5f ~ Sc 2 3 4 5 6

~ }f 7 8 9 10 11 ~rrWW 12 13 14 15 Fig. 4. Types of vestures (reprinted from Res. Bull. Coll. Exp. For. Hokkaido Univ. 33: 418, Ohtani & Ishida 1976, by permission of the Hokkaido University Forests Publisher).

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A c

B D Fig. 5. Drawings of transverse seetions of bordered pits. A: type A; B: type B, form I; C: type B, form 2; D: type B, form 3 (reprinted from Aeta Bot. Neerl. 27: 275, Van Vliet 1978, by permission of Blaekwell Seienee Publishers).

Van Vliet (1975) reported that some of the variation in papers on vestured pits is probably due to the fact that the nature of the pit pairs is not taken into account. Distinct differences in morphology of vestures among the pit types (i.e., intervessel pits; vessel-ray parenchyma pits, vessel-axial parenchyma pits and vessel-fibre pits) have been demonstrated by Ohtani and Ishida (1976) and Ohtani (1983). For instance in some woods the filamentous type can occur in the larger vessel-axial parenchyma pits but grade into small bead-like vestures in the smaller intervessel pits in the same cell. Ohtani and Ishida (1976) proposed 15 different types (Fig. 4) based on shape. Although their observations are very detailed, the use of these types is not practical since they intergrade. Moreover, one vestured pit mostly has a combination of many different types of individual protuberances. Nevertheless, Ohtani and Ishida (1976) concluded that the shape of vestures can be regarded as a common feature within a genus. Van Vliet (1978, 1979, 1981) recognised two major types of vestured pits in the Myrtales (Fig. 5): type A, in which the vestures are attached to all parts of the roof of the pit chamber and branch into a compact mass of vestures of nearly equal thickness, completely filling the pit chamber; and type B, in which a ring of trunk-like vestures is attached to the roof of the pit chamber, nearby the pit canal, pointing into the pit chamber and dichotomising to various extents into thinner branches. Considering the relative thickness of the trunks and the degree of branching of the vestures, three forms, BI, B2 and B3 are recognised in type B. These types are main1y based on observations of Combretaceae and related taxa in the Myrtales (Van Vliet 1978).

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A B c o

E F G H

Fig. 6. Drawings of transverse sections of bordered pits. A: type 1; B: type 2 (i); C: type 2 (ii); D: type 2 (iii); E: type 3 (i); F: type 3 (ii); G: type 4; H: type 5; v = vestures (reprinted frorn Bot. J. Linn. Soc. 100: 334, Nair & Mohan Ram 1989, by permission ofthe Academic Press).

Another classifieation system of vestured pits was proposed by Nair and Mohan Ram (1989; Fig. 6) based on observations of 66 taxa belonging to ten families. They distinguished 5 different vesture types: type 1 eorresponds with type A of Van Vliet (1978); type 2 with 3 subtypes in whieh vestures are attaehed to the pit ehamber wall and partly fill the pit ehamber; type 3 has two forms with small vestures not projeet­ ing into the pit ehamber; type 4 shows small vestures randomly distributed on the pit ehamber wall away from the outer pit aperture; and vestures in type 5 are absent or rarely present in the pit ehamber but spread over the inner pit aperture. Vestured pits of type 2 were found to be very eommon and those of type 3 and 4 very rare. Gener­ ally, specifie types of vestured pits were present throughout the vessels in a partieular speeies. Although these types are based on more divergent taxa than those of Van Vliet (1978), this typifieation has not been adopted by other authors and thus the taxonomie value or relevanee has not been tested for other plant groups. In addition to the morphology of vestured pits, numerous aeeounts on vesture morphology in softwood traeheids, and to a lesser extent vestured walls in hardwoods are reported in the literature. They are deseribed as spherieal, rounded eone, eonieal or eomplex (Cronshaw 1965; Liese 1965; Harada & Cöte 1985; Heady et al. 1994). The average diameter of 'warts' is between 100 and 500 nm, rarely up to 1 /1ill in diameter, and the average height between 500 nm up to 1 /1ill (Liese 1957; Ohtani

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1979,1983). Within one species the appearance and size (diameter at the base) varies to some extent and even between neighbouring cells remarkab1e differences exist. As for vestured pits, vestures associated with walls can be divided by shape into two main types: unbranched and branched (Ohtani et al. 1983). Heady et al. (1994) categorised vestures in the tracheids of Cypress pine (Callitris) into two types: large, nodulated vestures and small, hemispherica1 vestures. Nodules were described as hemispherical or tubular in shape having a smaller diameter than the diameter of the main trunk of the vesture and they occurred at varying positions on the vesture surface. The nodulated vestures resemble the branched vestures in hardwoods (as reported by Ohtani & Ishida 1976; Van Vliet 1978; Ohtani 1979; Ohtani et al. 1983; Harada & Cöte 1985; Castro 1988), aIthough in Callitris, the branches were usually found to be reduced in size to a bud-like, nodular form. They reported also anastomosing of vestures at their tops. Furthermore, Heady et al. (1994) found that mixed populations of the two vesture types occur. Note that Carlquist (1988a, 1989b) proposed the term 'verrucae' for vesture-like or wart-like structures observed in Cercidium (Fabaceae) because in this genus the excrescences that occur on vessel walls are much larger than usual vestures. More­ over, the shape of 'verrucae' tends to be angular or irregular and sometimes they are fused into lateral striae. In our opinion a new term such as 'verrucae' should not be created for protuberances that resemble vestures, even if they differ in size or shape. The very large variation in vesture size and shape has been demonstrated repeatedly. A more decisive argumentation to define a new character is based on the chemical composition or ontogeny. Moreover, Carlquist (1989b) noticed a continuum between vestures and 'verrucae' since he describes the vessel wall sculpture in Cercidium macrum as having 'small wart-like verrucae'. Parameswaran and Gomes (1981) and Baas and Zhang (1986) observed bud-like protrusions on the vessel wall of helical thickenings associated with vessel pits in Ligustrum. Although the size and shape of these structures do not suggest an immediate homology with vestures, both structures are comparable with each other. Similarly, Castro (1988, 1991) reported conspicuous vestures, which resemble 'verrucae', on helical thickenings in some species of Prosopis. A certain similarity can also be mentioned for the "swollen, rim-like extension of the pit canal and/or the secondary wall into the celllumen" present in some species of Cercidium (Schmid & Liese 1972; Carlquist 1989b); the structures were collectively termed 'crateriform pits'. In conclusion, classifying vestures is difficult due to the large number of interme­ diate forms. One may doubt whether a reliable general characterisation can be devel­ oped for vestures. It is hoped that a classification can be achieved after more SEM and rEM observations reveal their diversity.

DISTRIBUTION AND TAXONOMIC SIGNIFICANCE

Apart from few exceptions in the genus Pinus (Frey-Wyssling 1957) vestures are potentially present on tracheid walls of all gymnosperms (Liese 1957, 1965; Cronshaw 1965). The concentration of vestures often is variable between taxa or even within the

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same wood sampie. Ohtani and Fujikawa (1971) for instance, distinguished five dif­ ferent types in coniferous woods according to the number of vestures per unit area on the tracheid wall within an annual ring. As already mentioned, vestures also have been observed in monocotyledons, viz., bamboo species (Parameswaran & Liese 1977) and palms (Hong & Killmann 1992). Liese (1965) mentioned that in gymnosperms the variability and size of vestures reduces its value for purposes of identification. However, the alm ost complete ab­ sence of vestures in certain species and genera, as weIl as the predominance of smaller or larger vestures could be used to some advantage. For hardwoods, vestures have been reported in nearly 50 dicotyledonous families. Their presence in the vessels and tracheids of Gnetum (Scurfield et al. 1970; Parameswaran & Liese 1974; Carlquist 1994, 1995a, 1996a, b; Carlquist & Robinson 1995) has been interpreted as an additional argument for the close affinities of Gnetum with the angiosperms. Vestures are apparently absent on pits of tracheary elements of Welwitschia (Carlquist 1995b); the prominent bead-like protuberances on a tracheary element pit membrane in Welwitschia shown by Parameswaran and Liese (1974) must be pseudovestures rather than vestures. True vestures are thought to be absent on pit membranes. Vestures are distributed in all wood cell types although there is only one report of observations in septate wood fibres (Ohtani 1987) and two reports in wood paren­ chyma (Ohtani 1986; Hong & Killmann 1992). They are not only associated with pits but have been found to occur on helical thickenings of vessel walls (Ohtani & Ishida 1976; Ohtani et al. 1983, 1984b; Castro 1988, 1991), on remnant pit membranes of scalariform perforation plates (Butterfieid & Meylan 1974a), on the rim of simple perforation plates (Kucera et al. 1977; Rudall 1982; Vales 1983; Ohtani 1984; Fig. 22,23), and on trabeculae (Müller 1890; Meylan & Butterfieid 1973; Ohtani 1985). Our observations in Rubiaceae show that vestured perforations are frequently small, unusual and irregular (Fig. 22), demonstrating to some extent the homology between pits and vestures. It is not clear why in one wood sampie both vestured and nonvestured perforations are found. There is even one report of vestured pits outside the second­ ary xylem, namely in tracheoid cells of seeds of Fabaceae (Lersten 1982). Vestured pits are also observed in spiral tracheids of a fruit stalk of Conostomium quadrangulare (S. Dessein: personal communication). Hence, the presence of vestures is clearly not restricted to secondary xylem. Machado et al. (1997) observed vestured pits only in wood of roots and not in sterns of Styrax camporum (Styracaceae). In three species of Eucalyptus, Foster (1967) found no traces of vestures in vessel-ray pits through which tyloses developed nor were remnants of such structures found adhering to the outer surface of tyloses. En­ zymes secreted by the ray cell protoplast are thought to break down the pit membrane and the vestures in the pit chamber. Scurfield and Silva (1970) and Scurfield et al. (1970) confirmed this belief. A list of dicotyledonous families that have been reported to show vestures is given in Table 1 (pages 362-366). It is based on the list ofMetcalfe and Chalk (1983) and Carlquist (1982a, 1988a), and supplemented with recent records (e.g., Styracaceae:

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Machado et al. 1997; Dialypetalanthaceae: Piesschaert et al. 1997; Gentianaceae: Jansen & Smets 1998). Relevant references (except Carlquist 1982a, 1988a and Met­ calfe & Chalk 1983) are added for all families. In case of nonvestured taxa, only papers that explicitly comment on the absence of the feature are cited. These are our conclusions:

1. The following families that were reported by Record (1925) to show 'cribriform pits' lack vestures: Asteraceae, Clusiaceae, Hamamelidaceae, Hippocastanaceae and Scrophulariaceae. In contrast with data of Bailey (1933) vestures are absent in Malpighiaceae and Ochnaceae. Other families such as Coriariaceae and Coryno­ carpaceae, which are both included in the list of Metcalfe and Chalk (1983) and Carlquist (1988a), also do not show vestures; for Coriariaceae the absence of the character is confirmed by Suzuki and Yoda (1986). 2. Whether or not vestures are present in families such as Araliaceae, Capparidaceae, Chloranthaceae, Eupomatiaceae, or P1atanaceae should be checked by scanning electron microscopy. One may doubt whether the reports of vestured pits in Lau­ raceae by Moll and Janssonius (1906-1936) and Richter (1981) are true vestures. Castro (1985) found numerous pectocellulosic, nonlignified excrescences on the vessel-parenchyma pit membranes in some Lauraceae which are not artefacts but obviously different from pit vestures. These structures can be mi staken for vestures in the light microscope. 3. Vestures certainly will be found in more dicotyledonous families because the ab­ sence in several taxa is probably caused by a lack of investigations. When the intervessel pits are large and the vestures are coarse (e. g., in pits of 9-11 JlIIl in Terminalia, Van Vliet 1979), vestures are relatively easy to see with an oil-immer­ sion objective of a light microscope or even at lower magnification. But when the intervessel pits are minute (~4 JlIIl, e.g. in Rubiaceae), it is rather difficult or even impossible with the light microscope to see whether vestured pits are present or not. In these cases, only scanning electron microscopy provides decisive proof. For SEM observations it is necessary that during preparation of the wood specimen the pit field is sometimes split longitudinally to illustrate the structure clearly (see Fig.8-13). 4. Although vestures are often considered to characterise whole families and even orders such as Myrtales, Gentianales and Fabales, the list in Table 1 demonstrates that many exceptions exist. From the 52 families that are found to show vestured representatives, circa 23 families are thought to be entirely vestured. It is not im­ possible that within these families taxa without vestures can be found. Recently, for instance, J ansen et al. (in press) observed the absence of vestures in two Rubia­ ceae species. In the 29 remaining families the presence of vestures is restricted to some taxa. We presume that vestured and nonvestured representatives co-occur more frequently than hitherto known. Considering these remarks, the list in Table 1 has to be interpreted with caution and can only be regarded as preliminary.

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Table 1. List of dicotyledonous families (c1assification follows Mabberley 1997) that show representatives with vestured pits (VP) or vestured walls (VW) in their wood. Families printed in bold italic show genuine vestures; the presence of vestures is doubtful in fami­ lies printed in regular font style; SJ = personal observations of Steven Jansen.

Family Vestures present Vestures absent Aceraceae Acer (Ohtani 1979, 1983): VW

Apocynaceae 11 genera (Ing1e & DadswellI953a); Parsonsia (Ohtani et al. 1983); Nerium (Fahn et al. 1986); Alstonia (Wu et al. 1988; Sidiyasa & Baas 1998); 3 genera (Nair & Mohan Ram 1989); Dictyo- phleba (Fig. 18); Gonioma, Malouetia, Tabernaemontana (Fig. 23; SJ): VP + VW Aquifoliaceae Ilex chiapensis: VW?, Ilex cymosa: Ilex (Baas 1973; Ohtani & VP? (Baas 1973); Ilex (Ohtani 1979): Ishida 1976; Ohtani 1983) VW Araliaceae Pseudopanax (Ohtani et al. 1983; Pseudopanax, ScheLffera Butterfieid et al. 1984): VW (Meylan & Butterfieid 1974); 5 genera (Ohtani & Ishida 1976); ScheLffera (Ohtani et al. 1983)

Asclepiadaceae Calotropis, Periploca (Fahn et al. 1986), Asclepias, Calotropis (Fig. 10), Cryptostegia, Dregea (SI): VP + VW

Boraginaceae Echium, Rochefortia, Pteleocarpa, Auxemma, Cordia, Ehretia, partially in Bourreria & Heliotropium Heliotropium, Patagonula, (Miller 1977); Lepidocordia, Pteleo- Saccellium, Tournefortia carpa (Gottwald 1982); rare in Cordia (Miller 1977); Auxemma, Cor- (Barajas Morales 1981; Gottwald 1983; dia, Patagonula (Gottwald Nair & Mohan Ram (1989): VP 1983)

Brassicaceae Schouwia, Hemicrambe (Kowal & Cutler 1975); Zilla spinoza (Fahn et al. 1986): VP Buddlejaceae Nuxia, Buddleja (Coulaud 1989): VP Androya, Buddleja, Gompho- stigma, Nuxia, Peltanthera (Mennega 1980); Nuxia (Jansen & Smets 1998)

Capparidaceae 8 genera (Bailey 1933): VP Oceanopapaver (Schmid et al. 1984)

Chloranthaceae Ascarina lucida (Ohtani et al. 1983): Ascarina (Meylan & Butter- VW field 1974; Carlquist 1990)

Cistaceae Cistus, Fumana (Baas & Werker 1981); obscure vestures in Cistus (Fahn et al. 1986): VP

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(Table 1 continued) Family Vestures present Vestures absent Combretaceae numerous genera (Rao 1972; Van Vliet 1978,1979; Carreras & Vales 1986; Wu et al. 1988; Nair & Mohan Ram 1989; Alfonso & Richter 1991): VP + VW Cornaceae Cornus (Ohtani 1979); Kaliphora Griselinia (Meylan & Butter- (Carlquist 1989c): VP + VW field 1974; Ohtani et al. 1983); Cornus (Ohtani 1979; SJ); 10 genera (Noshiro & Baas 1998) Crypteroniaceae Alzatea, Axinandra, Crypteronia, Dac- tylocladus (Van Vliet 1975); Alzatea (Baas 1979): VP + VW Cyrillaceae Clethra (Ohtani 1979, 1983): VP + VW Dialypetalanthaceae (Piesschaert et al. 1997): VP Dipterocarpaceae 13 genera (Gottwald & Parameswaran 1966; Brazier 1979): VP Elaeagnaceae Elaeagnus, Hippophae, Shepherdia (SJ): VP Ericaceae Lyonia, Enkianthus (Ohtani 1979); Pieris (Ohtani 1979); Pieris, Enkianthus (Ohtani 1983): VP + VW Lyonia, Vaccinium (Ohtani 1983); Arbutus (SJ) Euphorbiaceae Aleurites, Sapium (Ohtani 1979; 1983); Aleurites, Mal/otus, Sapium Bridelia (Mennega 1987); Cleistan- (Ohtani & Ishida 1976); Mal- thus (Wu et al. 1988); Bridelia, occur- lotus (Ohtani 1979); 42 genera rence rare in Phyllanthus (Nair & (Mennega 1987); 5 genera Mohan Ram 1989): VP + VW (Nair & Mohan Ram 1989) Eupomatiaceae Eupomatia bennettii (Woodland 1982): Eupomatia laurina (Wood1and VP 1982; Carlquist 1992) Fabaceae numerous taxa (e.g., Schmid & 14 genera (Quirk & Miller Machado 1964; Schmid 1965; Meylan 1983, 1985); Bauhinia (Nair & Butterfieid 1974; Ohtani & Ishida & Mohan Ram 1989); note 1976; Ohtani 1979; Cassens 1980; that all species without ves- Baretta-Kuipers 1981; Ohtani 1983; tures belong to the tribe Cas- Ohtani et al. 1983, 1984b; Fahn et al. sieae or Cercideae from sub- 1986; Wu et al. 1988; Castro 1988, family Caesalpinioideae 1991; Car1quist 1989b; Fujii & Baas 1989; Nair & Mohan Ram 1989; Den Outer & Van Veenendaal 1992; Heenan 1997): VP + VW Fagaceae Fagus, Castanopsis (parham & Baird Nothofagus (Meylan & Butter- 1974); Fagus, Quercus, Castanea, field 1974; Gale 1982; Ohtani Castanopsis (Ohtani 1979, 1983): et al. 1983); Fagus, Quercus, VP+VW Castanea, Castanopsis (Ohta- ni & Ishida 1976); Quercus (Ohtani 1979) Gelsemiaceae Mostuea (Mennega 1980): VP Gelsemium (Mennega 1980)

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(Table 1 continued) Family Vestures present Vestures absent Geniostomaceae Geniostoma (Meylan & Butterfieid 1974,1978); Geniostoma, Labordia (Mennega 1980): VP + VW Gentianaceae Anthocleista, Fagraea, Potalia (Men- nega 1980); 5 genera (Jansen & Smets 1998); Tapeinostemon (Fig. 11; SJ): VP Grossulariaceae Ixerba (Meylan & Butterfieid 1978); Carpodetus, Ixerba, Quin- Ixerba, Quintinia (Ohtani et al. 1983); tinia (Meylan & Butterfieid Grevea, Montinia (Carlquist 1989c): 1974) VP+VW Illiciaceae Illicium (Ohtani 1979): VW Illicium (Ohtani 1979) Lamiaceae Clerodendrum, Gmelina, Vitex Vitex (Meylan & Butterfie1d (Mathew & Shah 1983): VP 1974; Ohtani et al. 1983); Cle- rodendrum (Ohtani & Ishida 1976; Ohtani 1983) Gmelina (Nair & Mohan Ram 1989) Lauraceae Sassafras albidum (parham & Baird Beilschmiedia, Litsea (Meylan 1974): VW; Aiouea, Aniba, Eusider- & Butterfieid 1974; Patel oxylon, Licaria, Dehaasia, Notha- 1987); 5 genera (Ohtani & phoebe, Ocotea, Persea (Richter Ishida 1976); 5 genera (Ohta- 1981): VP ni 1983); Ocotea, Persea (SJ) Lythraceae numerous genera (Ohtani & Ishida 1976; Baas & Zweypfenning 1979; Ohtani 1979,1983; Graham et al. 1986, 1987; Baas 1986; Nair & Mohan Ram 1989): VP + VW Magnoliaceae Liriodendron (Ohtani 1989): VW Michelia, Magnolia (Ohtani 1979); 5 genera (Chen et al. 1993) Melastomataceae numerous genera (Van Vliet 1978; Koek-Noorman et al. 1979; terWelle & Koek-Noorman 1981; Van Vliet 1981; terWelle & Detienne 1993): VP+VW Meliaceae VP only in certain vessel members Melia, Cedrela (Ohtani & Ishi- of Soymidafebrifuga (Nair & Mohan da 1976); Dysoxylum (Meylan Ram 1989) & Butterfieid 1974; Ohtani et al. 1983); Melia, Cedrela (Ohtani 1983); Soymida (SJ) Moraceae Streblus (Ohtani et al. 1983): VW Morus, Broussonetia, Ficus (Ohtani 1979; ter Welle et al. 1986a, b); Artocarpus, Ficus (Nair & Mohan Ram 1989) Myrtaceae numerous genera (e. g. Ingle & Dads- weIl 1953b; Meylan & Butterfieid 1J,

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(Table 1 continued) Farnily Vestures present Vestures absent (Myrtaceae continued) 1974; Butterfieid & Meylan 1974a; Baas 1977; Ohtani et a1. 1983; Fahn et a1. 1986; Wu et a1. 1988; Nair & Mohan Rarn 1989; Nair 1989; Dias- Lerne et a1. 1995): VP + VW Oleaceae Ligustrum (Ohtani & Ishida 1976; Nestegis (Meylan & Butter- Ohtani 1983); Fraxinus (Wheeler field 1974; Ohtani et a1. 1983); 1981); Chionanthus, Fraxinus, Ligus- Osmanthus, Syringa, Fraxinus trum, Olea (weakly vestured), Syringa (Ohtani & Ishida 1976); Os- (Baas & Zhang 1986); Schrebera manthus, Syringa, Fraxinus (Nair 1987; Nair & Mohan Rarn 1989); (Ohtani 1983); 9 genera (Baas 11 genera (Baas et a1. 1988): VP & Zhang 1986); 20 genera (Baas et a1. 1988) Oliniaceae (Mujica &Cutler 1974); Olinia (SJ): VP

Onagraceae Fuchsia (Meylan & Butterfieid 1974; Oenothera, Calylophus (Carl- Ohtani et a1. 1983); 12 genera (Carl- quist 1975b, 1982a) quist 1975a); Epilobium, Fuchsia (Carlquist 1977); 5 genera (Carlquist 1982a): VP+ VW

Penaeaceae 6 genera (Carlquist & Debuhr 1977): VP Platanaceae Platanus occidentalis (parharn & Platanus kerrii (Wheeler Baird 1974): VW 1995) Polygonaceae Muehlenbeckia (Kucera et a1. 1977; Coccoloba (SJ) Ohtani et a1. 1984b); Brunnichia, Tri- plaris (SJ): VP

Proteaceae Toronia (Butterfieid & Meylan 1974b; Knightia (Meylan & Butter- Ohtani et a1. 1983); Garnieria (Lanyon field 1974; Ohtani et a1. 1983; 1979); Helicia (Ohtani 1979); Aci- PateI1992); Helicia (Ohtani donia, Pycnonia, Persoonia s. str. & Ishida 1976); 2 genera (Patel 1992): VP + VW, (Lanyon 1979); Grevillea (Nair & Mohan Rarn 1989) Punicaceae Punica (Bridgwater & Baas 1978; Fahn et a1. 1986): VP + VW Rhamnaceae Zizyphus (Ohtani 1979, 1983); un- Discaria (Meylan & Butter- cIear w hether true vestures or pseudo- field 1974; Ohtani et a1. 1983); vestures are present in 6 genera Zizyphus, Hovenia (Ohtani (Schirarend 1991): VP + VW & Ishida 1976); 10 genera (Schirarend 1991); Condalia, Karwinskia, Zizyphus (SJ)

Rhynchocalycaceae Rhynchocalyx (Van Vliet 1975): VP + VW

Rosaceae Spiraea (Zhang & Baas 1992); Prunus nurnerous taxa (Meylan & (Ohtani 1979): VP + VW Butterfieid 1974; Ohtani & Ishida 1976; Ohtani 1979, 1983; Zhang & Baas 1992)

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(Table 1 continued) Family Vestures present Vestures absent Rubiaceae nurnerous genera (Koek-Noorrnan Tarenna, Pavetta (Jansen et al. 1969; Meylan & Butterfieid 1974; in press) Rogers 1981, 1984; Rudall 1982; VaIes 1983; Ohtani 1984, 1986, 1987; Wu et al. 1988; Nair & Mohan Rarn 1989; Jansen et al. 1997a, b, in press); Theli- gon um (Ronse Decraene: personal cornrnunication): VP + VW (Fig. 8, 9, 12-17,19-22,24-27) Sabiaceae Meliosma (Ohtani 1979, 1983): VP + Meliosma (Ohtani 1979) VW Sonneratiaceae Duabanga, Sonneratia (Rao et al. 1987a, b); Duabanga (Wu et al. 1988): VP+VW Staphyleaceae Euscaphis (Ohtani 1979): VW Euscaphis (Ohtani 1983); Staphyllea (SJ) Strychnaceae Strychnos (Cockrell 1941); 7 genera (Mennega 1980); Bonyunia (Coulaud 1989): VP Styracaceae in root wood of Styrax (Machado et al. Styrax, Pterostyrax (Ohtani 1997): VP 1983); in stern wood of Styrax (Machado et al. 1997); Styrax (SJ) Symplocaceae Symplocos (Ohtani 1979, 1983): VP + Symplocos (Ohtani 1979, VW 1983; SJ) Theaceae Stewartia, Cleyera, Eurya (Ohtani 2 genera (Ohtani 1979); 1979); Eurya (Ohtani 1983): VP + VW 4 genera (Ohtani et al. 1983); 12 genera (Deng & Baas 1990); 6 genera (Deng & Baas 1991) Thymelaeaceae Daphne (Ohtani & Ishida 1976); Daphne (Ohtani 1983); Pime- Pimelea (Ohtani et al. 1984b); Thy- lea (Ohtani et al. 1983) melaea (Fahn et al. 1986); Aquilaria (Rao & Dayal 1992): VP Trochodendraceae Trochodendron (Ohtani 1979): VW Verbenaceae Tectona (Gottwald & Pararneswaran 4 genera (Mathew & Shah 1980); Citharexylum, Lantana, Tecto- 1983); Tectona (Nair & na (Mathew & Shah 1983): VP + VW Mohan Rarn 1989) Vochysiaceae 6 genera (Quirk 1980); Callisthene (SJ): VP Winteraceae Pseudowintera (PateI1974; Meylan & Pseudowintera (Meylan & Butterfieid 1982; Ohtani et al. 1983); Butterfieid 1974); Zygogonum Drimys (Carlquist 1988b, 1989a): VW (Carlquist 1983); Drimys (Carlquist 1988b, 1989a) Zygophyllaceae Balanites, vestigial vestures in Guaia- 17 genera (Sheahan & Cutler cum, Bulnesia (Pararneswaran & Con- 1993) rad 1982); Balanites (Fahn et al. 1986; Sheahan & Cutler 1993): VP

Downloaded from Brill.com10/05/2021 09:04:58AM via free access § Cf' (1) P 11_I C/) I ~ I POI.YGONAI.ES J Cf' I Ro tIi I I ~ /...... IlAI.SA.IIN',\..ESIIA\-SAMIN"'\..E~ Q ~ Cf' / '-... / ...... / NYMPHAEAI.ES . N'MP~ . ~ Cf'

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AALES \ via freeaccess 0\""' Fig. 7. The distribution of vestures plotted on Dahlgren's c1assification system of 1989. -J 368 IAWA Journal, Val. 19 (4), 1998

Fig. 8-15. Vestured pit chambers. - 8: Palicourea crocea (Tw 38180, Rubiaceae), vestures sparsely present. - 9: Feretia apodanthera (Tw 52597, Rubiaceae), small vestures present around pit canal. - 10: Calotropis procera (BR: R. Germain 2354, Asclepiadaceae). - 11: Ta­ peinostemon longiflorum (Tw 36659, Gentianaceae). - 12: Chimarrhis turbinata (Tw 25849,

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As previously done by Van Vliet and Baas (1984), we used Dahlgren's (1989) clas­ sification diagram to plot the distribution of vestures in dicotyledons (Fig. 7). In this diagram, the position of the orders in relation to each other is determined as far as possible by the degree of similarity, reflecting the supposed phylogenetic relation­ ships. The system is most useful to permit a quick and effective survey of the distribu­ tion of any character. It also offers a chance to predict a 'yet-unknown' character in a species of a family from known characters in the neighbouring families (Dahlgren 1980). Figure 7 clearly demonstrates that vestures have arisen independently a number of times or, in other words, that the character is polyphyletic within the dicotyledons. Note that we do not use the much cited and famous chloroplast DNA-tree of Chase et a1. (1993) for showing the distribution of vestures. Plotting the feature on this tree will give no additional information than that the feature has been evolved several times in xylem evolution. In our opinion, the mapping on a cladogram such as the Chase-tree is more useful to evaluate the distribution of character changes in selected clades (cf. Baas & Wheeler 1996). We presume that vestures are so homoplastic in xylem evolution that the potential for using vestures in phylogenetic reconstructions at a high taxonomic level is seriously reduced. Bailey (1933) found that vestured pits occur throughout, or are particularly charac­ teristic of certain taxonomic groups. From the 25 families having vestured pits, only 4 families, namely Euphorbiaceae, Fabaceae, Ochnaceae and Oleaceae, showed ves­ tured pits in certain but not a11 specimens examined. However, the presence of the character was found to be closely correlated with the systematic subdivision of these families except for the Oleaceae. Hence, Bailey (1933: 272) stated that vestured pits "are of considerable value both in the systematic study of woods and in discussions conceming the relationships and classification of specific groups of dicotyledons." He showed that two wood sampies of different families that very closely resemble each other, for instance those of Maclura pomifera and Robinia pseudoacacia, may be identified easily by the fact that vestured pits are present in one family (Fabaceae) but absent in the other one (Moraceae). Another proof to demonstrate the diagnostic value of vestured pits is shown by the first lead in the key to European woods by Jacquiot et a1. (1973) which is on presence or absence of vestured pits. Thus the oc­ currence of vestured pits remains of great general taxonomic interest because they help to identify taxa in such families as Rubiaceae, Fabaceae etc. (see Table 1). When we try to attribute some taxonomic value to the morphology of vestures, the problem is that different types of vestures can integrade as pointed out above. The diagnostic and systematic value of vesture types is therefore restricted. Several inves­ tigators concluded that the distribution of vesture types is not congruent with our views on any system below the family level, in e.g. Boraginaceae (Miller 1977),

~ Rubiaceae), vestures attached upside down to the pit membrane (scale bar = 1 JlIll). - 13-15: Coussarea vallis (Tw 39656, Rubiaceae). - 13: Large, branched vestures filling the pit cham­ ber. - 14 & 15: Lateral view of vestured pit showing pit canal and pit membrane.

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Fig. 16. Oxyanthus unilocularis (Tw 22972, Rubiaceae), pit aperture sparsely vestured. - Fig. 17. Psychotria brachiata (Tw 49905, Rubiaceae), pi! apertures showing branched vestures. - Fig. 18. Dictyophleba lucida (BR: A. Sapin 673, Apocynaceae), vestures completely occ1ud­ ing the pit aperture of vessel-ray parenchyma pits. - Fig. 19-20. Didymosalpinx lanciloba (BR: J. Louis 9768, Rubiaceae). - 19: Detail of pit aperture and vestures. - 20: Vestured fibre pits viewed from the outer surface. - Fig. 21. Triainolepis africana (BR: J.B. Gillet & S.P.

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Fig. 24 & 25. Vestured vessel walls. - 24: Genipa americana (Tw 25580, Rubiaceae), vestured helical thickenings. - 25: Pentagonia macrophylla (Tw 43043, Rubiaceae), detail of large nodulated vestures. - Fig. 26. ArgocojJeopsis suhcordata (BR: J. Louis 3054, Rubiaceae). - Fig. 27. Calycosiphonia spathicalyx (BR: J. Dubois I, Rubiaceae).

Lythraeeae (Baas & Zweypfenning 1979), Cistaeeae (Baas & Werker 1981), Verbena­ eeae (Mathew & Shah 1983) and Oleaeeae (Baas et al. 1988). Also, Cassens (1980) did not find vesture types that eould be used to differentiate the many generie segre­ gates of Pithecellobium. On the other hand, Van Vliet (1978) found a eonsisteney of his vesture types within intervessel pits of Combretaeeae. He stated that the major types of vestures follow the subfamily classifieation ofthe Combretaeeae: typeA in Strephonematoideae and type B2 and B3 in Combretoideae. In other families of the Myrtales the distribution of his vesture types were rarely eongruent with the taxonomie classifieation (Van Vliet 1978; Van Vliet & Baas 1984). Furthennore, his vesture types eould be arranged into a gradual series going from typeA, via type BI to type B3. Van Vliet and Baas (1984) based this hypothetieal speeialisation trend within a number of Myrtales families

f- Kibuwa 19850, Rubiaceae), detail of vestured fibre pit viewed from the inner surface. - Fig. 22. Psychotria vasivensis (Tw 36695, Rubiaceae), small and vestured simple perfora­ tions. - Fig. 23. Tabernaemontana ventricosa (BR: A. Michelson 1074, Apocynaceae). vestured simple perforation (scale bar = 10 ).IIIl).

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(e.g., Combretaceae, Sonneratiaceae and Lythraceae) on the fact that type A mostly occurs in the representatives that have retained the highest number of primitive at­ tributes in their wood. Note that all Myrtales comprising Combretaceae, Lythraceae, Melastomataceae (incIuding Crypteroniaceae), Myrtaceae, Oliniaceae, Onagraceae, Penaeaceae, Punicaceae, Psiloxylaceae, and Sonneratiaceae are completely vestured (Van Vliet & Baas 1984). They also treated the Thymelaeaceae in the Myrtales and concIuded that the Rhizophoraceae and the Lecythidaceae should be excIuded from the core Myrtales because these two families lack vestured pits and internal phloem. Other taxa in which vesture morphology is congruent with taxonomic cIassifications are the genus Prosopis in Argentina (Castro 1988) and the tribe Pavetteae in the Rubia­ ceae (Jansen et al. in press). Ohtani and Fujikawa (1971), Ohtani (1979), Ohtani et al. (1983), ButterfieId et al. (1984) and Ready et al. (1994) concIuded that the shape, size, and density of distribu­ tion of vestured walls within a species is sufficiently characteristic to be used as an aid to wood identification. The study by Ohtani et al. (1983) revealed a correlation between vesture occurrence and fibre type. Vestures appear to be absent in Iibriform fibres (single report in Damnacanthus indicus, Ohtani 1987) but are confined to fibres with distinctIy bordered pits (fibre-tracheids). Apart from this, both vestured vessel and fibre walls occur randomly within the dicotyledons. In particular taxa, the variability in presence or absence of vestured pits contrasts strongly with its consistent presence in large assemblages, e.g. the Gentianales and Myrtales. Quirk and Miller (1983, 1985), for example, observed nonvestured pits in Koompassia and in three subtribes of the Fabaceae. If a single wood sampIe of a species, however, is found to be nonvestured while other related specimens are con­ sistently vestured, we should first doubt whether the wood sampIe is correctly identi­ fied or whether an error in the collection of wood specimens has been made. Our own observations on wood of Rubiaceae proved that specimens that were nonvestured were most Iikely misidentified. Subsequently, it is important to find out whether ab­ sence of vestures is constant for a taxon. The gradual variation of conspicuous presence, via vestigial presence to total ab­ sence of vestures in some taxa opens interesting possibilities to hypothesise on the phylesis of vestures. Fahn (1967) stated that vestures are found in phylogenetically more developed xylem and that vestured pits are considered to be advanced. On the basis of a very limited number of wood sampIes Parham and Baird (1974) thought scalariform perforation plates are more common in woods with vestures. Rowever, when a larger assemblage ofwoods is examined, the occurrence ofvestures and warts cannot be placed in any evolutionary context (Scurfield et al. 1970, Meylan & But­ terfield 1974). Although the presence of vestured pits may be an important character in determin­ ing affinities of fossil material (e.g., Srivastava 1994; Cevallos-Ferriz & Barajas Morales 1994), it is very often difficult to recognise vestured pits in fossil woods (see above) making their value as a diagnostic feature doubtful in these cases (e.g., ButterfieId & Meylan 1980; Wheeler & Baas 1992).

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In eonclusion, the great variation in loeation, size, and shape of vestures in some speeies makes the presenee of these struetures often of greater taxonomie signifieanee than their mieromorphology. Even if a better typifieation has been aehieved, eaeh taxon should be examined separately beeause in partieular taxa the eharaeter has sys­ tematie signifieanee while in other taxa no eongruenee with the taxonomie system ean be found. Finally, it is hoped that we willieam more about the possible influenee of environmental faetors on the morphology of vestures. This aspeet is also important to fully understand the true taxonomie signifieanee of vestures.

CONCLUSIONS

Vestures and warts are likely to be homologous features as proposed by several au­ thors (Cöte & Day 1962; Seurfield & Silva 1970; Seurfield et al. 1970; Meylan & Butterfieid 1974; Ohtani & Ishida 1976; Van Vliet 1978; Ohtani 1983; Ohtani et al. 1984a), even if they vary eonsiderably in shape, size and distribution. It is not clear, however, whether all types of vestures and warts are homologous. Ultrastruetural research by TEM making an in-depth study of the development (eell wall deposition, lignifieation) of vestures is clearly needed. The few previous studies on the ontogeny of vestures are somewhat restrieted and outdated. Moreover, literature on the ehemi­ eal eomposition and possible funetions are contradictory. The list of families in whieh vestures oeeur is only preliminary and should be interpreted with eaution. It should also be investigated to what extent vestures are eommon outside seeondary xylem. Another interesting question is in whieh taxa the eharaeter is apomorphie or plesio­ morphie or at what stages in phylogeny vestures have originated. Sinee numerous questions remain unanswered, we hope that this review will serve as a base for further diseussions and research on this topie.

ACKNOWLEDGEMENTS

We are grateful to Dr. E.A. Wheeler for helpful comments on the occurrence of vestures in fossil wood and to Prof. Dr. W. Liese for checking literature on warts. For sending valuable reprints, we would like to thank Dr. W.A. Cöte, Dr. P. Kitin, Dr. A.M.W. Mennega, Dr. J. Ohtani, and Dr. A. Takahashi. Dr. H. Beeckman (Royal Museum for Central Africa, Tervuren) and the director of the National Botanic Garden of Belgium are acknowledged for the supply of wood sampIes. Steven Jansen holds a scholarship of the Research Council of the K. U. Leuven. This research is supported by agrant from the Research Council of the K. U. Leuven (OT/97/23) and by grants from the Fund for Scientific Research - Flanders (F.W.O., Belgium): project numbers 2.0038.91 and G. 0143.95.

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