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. Downloaded from Brill.com10/05/2021 09:04:58AM via free access Jansen, Smets & Baas - Vestures in woody plants 349 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). Downloaded from Brill.com10/05/2021 09:04:58AM via free access 350 IAWA Journal, Vol. 19 (4),1998 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)