IAWA Journal, Vol. 19 (1),1998: 35-42

VESTURED PITS IN SOME WOODY by Steven Jansen & Erik Smets Botanical Institute, Laboratory of Systematics, K. U. Leuven, Kard. Mercierlaan 92, B-3001 Heverlee, Belgium

SUMMARY

Vestured pits are reported for the first time in representatives of four genera of Gentianaceae, namely Lisianthius, Macrocarpaea, Symbol­ anthus and Tachiadenus. All vestures observed were small to very small and occur at the roof of the pit chamber near the outer pit aperture. Some also show sparsely vestured inner pit apertures. The logani­ aceous genera and Fagraea, often included in Gentiana­ ceae, were also investigated. Key words: Vestured pits, Gentianaceae, , .

INTRODUCTION

Vestured pits are known to occur in many woody . They are defined as pits with the pit cavity and/or aperture wholly or partly lined with projections from the sec­ ondary cell wall (IAWA Committee 1989). Bailey (1933) examined 2660 species of 979 genera belonging to 152 families. He found vestured pits in about 25 families. Other reports on vestured pits since Bailey' s classical work are, e. g. Gnetum (Scurfield et al. 1970; Parameswaran & Liese 1974; Carlquist 1994, 1996a, 1996b; Carlquist & Robinson 1995), Proteaceae (ButterfieId & Meylan 1974); Crypteroniaceae (Van Vliet 1975); Boraginaceae (Miller 1977), Cistaceae (Baas & Werker 1981) and Styracaceae (Machado et al. 1997). Until now the feature has been reported in about 50 dicotyle­ donous families characterising taxa such as Fabaceae, Euphorbiaceae, Dipterocarpa­ ceae and all Myrtales. Vestured pits are also present in many families of the Gentianales: Apocynaceae (Bailey 1933; Ohtani et al. 1983; Jing et al. 1988; Nair & Mohan Ram 1989),Asclepi­ adaceae (Record 1925; Bailey 1933), Dialypetalanthaceae (Piesschaert et al. 1997), Loganiaceae (Bailey 1933; Meylan & Butterfield 1974), and (Bailey 1933; Koek-Noorman 1969; Meylan & ButterfieId 1974) but the character has not been re­ ported in Gentianaceae. Carlquist (1984, 1992) noted that the absence of vestured pits in Gentianaceae can be an artefact caused by the very few investigations that have been made. Moreover Gentianaceae are a predominantly herbaceous family compris­ ing few genera which are shrubby or rarely small , e. g. Macrocarpaea, Lisianthius, Symbolanthus, Chorisepalum, Exacum, Tachiadenus, Chironia and Orphium. The loganiaceous tribe Potalieae which comprises Potalia, Anthocleista and Fa­ graea according to Leeuwenberg and Leenhouts (1980), has been included in the

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Gentianaceae by several authors (Bureau 1856; Fosberg & Sachet 1974,1980; Struwe et al. 1994). This transfer has also been supported by Downie and Palmer (1992) and Olmstead et al. (1993) on the basis of molecular data. Mennega (1980), however, found that wood anatomy does not support inclusion of the tribe in the Gentianaceae and she suggested a rather isolated position within the Loganiaceae. We must also add that Leeuwenberg (1997) disagreed with splitting the Loganiaceae and kept the tribe Potalieae within Loganiaceae. While preparing a review manuscript on vesturing and in addition to our ongoing wood anatomical study of the Rubiaceae, we investigated wood of some shrubby Gentianaceae and specimens ofthe genera Anthocleista, Fagraea andNuxia. The aim of our study was to find out whether vestured pits were truly absent or whether their reported absence was only due to the lack of detailed scanning electron microscopical investigations.

MATERIAL AND METHODS

All wood sampies of Gentianales were taken from BR herbarium specimens. The diameter of the twigs does not exceed 1 cm. The specimens examined are listed be­ low with reference to their origin and collector. A radial and/or tangential surface was obtained by cutting with a sliding microtome or by splitting the wood. Both methods showed vessel pits in such a way that the pit membrane and underlying pit chamber were visible. In order to eliminate the presence of pseudovestures, the sam­ pIes were treated with household bleach (15 % sodium hypochlorite) for one hour to rernove extraneous or coagulated material from the pit chamber (Exley et al. 1974; Gale 1982). All sampies were coated with gold and examined with a Jeol JSM-6400 scanning electron microscope. An accelerating voltage of 27 kV was used to make photographs. At least ten pits were measured to record their horizontal pit diameter.

List 0/ material studied - Gilg, Congo, Upemba, Robyns 3599; A. vogelii Planeh., Iocality unknown, C. de Briey 230. - Fagraea sp., Iocality unknown, Von Martius. - Lisianthius nigrescens Griseb., Mexico, collector unknown; L. nigrescens Griseb., Mexico, Orizaba, M. Bourgeau 2565; L. seemanii (Griseb.) O. Kuntze, Costa Rica, Santa Bar­ bara, H. Pittier & Th. Durand 1670. - Macrocarpaea obtusifolia Griseb., Brazil, collector un­ known; Macrocarpaea sp., Iocality unknown, Linden 164. - Nuxia congesta R. Br. ex Fresen., Congo, Virunga, J. Lebrun 4905. - Symbolanthus pulcherrimus Gilg, Costa Rica, Aho deI Pal­ mital, H. Pittier & Th. Durand 4018; Symbolanthus sp., locality unknown, Von Martius. - Tachiadenus longiflorus Griseb., Madagascar, Antananarivo, L.J. Dorr 3681.

RESULTS

Since vessels in Tachiadenus longiflorus are solitary and embedded in a tissue mainly consisting of fibre-tracheids, most pits of this species observed by SEM must be ves­ seI to fibre-tracheid pits. For the other species studied, however, vessel grouping is not known and therefore it is sometimes impossible to determine the pit type.

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Fig. 1-6. Vessel pits of Anthocleista and Fagraea species. - 1: Anthocleista vogelii, branched vestures viewed from the outer surface. - 2: A. vogelii, non-vestured inner pit apertures. - 3: A. grandiflora, vestured intervessel pits viewed from the outer surface. - 4: A. grandiflora, detail of few branched and very small unbranched vestures near the outer pit aperture. - 5: A. gran­ diflora, non-vestured vessel-ray pits. - 6: Fagraea sp., non-vestured vessel pits.

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Fig. 7-12. Vessel pits of Lisianthius and Macrocarpaea species. -7: Lisianthius nigrescens, vestured pits viewed from the outer surface. - 8: L. seemanii, vestured outer pit apertures. - 9: L. seemanii, vestured pit chambers. - 10: L. seemanii, inner pit apertures sparsely vestured. - 11: Macrocarpaea obtusifolia, vestured pits viewed from the outer surface. - 12: M. obtusi­ folia, inner pit apertures sparsely vestured.

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Fig. 13-16. Vestured vessel pits of Symbolanthus and Tachiadenus, viewed from the outer sur­ face. - 13 & 14: Symbolanthus pulcherrimus, vestures sparsely present. - 15: Symbolanthus sp. - 16: Tachiadenus longijlorus.

All vessel pits are alternate and bordered to distinctly bordered. The diameter of all gentianaceous vessel pits and Nuxia congesta is minute: on average 3 or up to 4 f.Ull large. Small sized pits occur in Anthocleista (on average 5 /lm in A. vogelii, Fig. 1, and about 6.5 /lm inA. grandij1ora, Fig. 3,4,5), while medium sized pits are found in Fagraea (on average 7.5 /lm, Fig. 6). With the exception of Fagraea (Fig. 6) and Nuxia congesta, all sampies investi­ gated show vestured pits (Fig. 1, 3,4, 7-16) although the vestures are sometimes sparsely present (e.g. Fig. 14). The vestures in specimens with minute pits could only be seen with the scanning electron microscope and not with the light microscope (even when using an oil immersion objective). In Anthocleista grandiflora most pits are vestured (Fig. 3, 4); however, we observed few vessel elements with non-vestured pits (Fig. 5). As far as we could see, these pits are vessel-ray pits.

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The vestures always occur at the roof of the pit chamber, near the outer pit aper­ ture. While few larger vestures are often branched, forked and irregular in shape (e.g. Fig. 1, 3,4), most vestures are very small, unbranched, and dotted, conical or rod­ shaped (e.g. Fig. 7, 9,15,16). Inner pit apertures are usually not vestured (Fig. 2). In Lisianthius nigrescens, L. seemanii (Fig. 10), Macrocarpaea obtusifolia (Fig. 12) and Tachiadenus longiflorus the inner pit apertures are also sparsely vestured. Vestures on the inner vessel walls were not present in the material investigated nor did we observe vestured fibre pits. Vessel-ray pits appear to be similar to intervessel pits in size and shape throughout the ray cello Only one vestured simple perforation plate was found in Lisianthius seemanii and Symbolanthus sp. Note that, apart from vestures, the wood of Anthocleista and Fagraea shows small prismatic crystals in axial parenchyma cells.

DISCUSSION AND CONCLUSION

This is the first report on the occurrence of vestured pits in the secondary xylem of Lisianthius, Macrocarpaea, Symbolanthus and Tachiadenus ofthe Gentianaceae. This study demonstrates that vestured pits are possibly present in all woody Gentianaceae and in more families than is presently known because the absence of vestures can simply be caused by a lack of investigations with the scanning electron microscope. The observation of some non-vestured pits in Anthocleista grandiflora (Fig. 5) rnight be explained by the fact that occurrence and morphological variation of vestures in pits of vessel walls varies in many cases according to pit types (intervessel pits, vessel-ray pits, vessel-axial parenchyma pits, vessel-wood fibre pits) as demonstrated by Ohtani and Ishida (1976). We presume that the vessel-ray pits in Anthocleista grandiflora are non-vestured while other pit types are clearly vestured. One should note, however, that during SEM investigation it is often difficult to determine which type of vessel pit is observed. A more detailed scanning electron microscopical study of all woody Gentianaceae would be necessary to evaluate the diagnostic value at and below the family level. The Loganiaceae are usually listed among the families with vestured pits (Bailey 1933; Metcalfe & Chalk 1983). However, Mennega (1980) showed that many excep­ tions exist: Gelsemium, Logania, Retzia, and all genera of the Buddlejeae do not have vestured pits. The specimens of Fagraea (Potalieae) andNuxia congesta (Buddlejeae) studied here show non-vestured pits. The reports on the presence (not illustrated) of vestured pits in Nuxia and Buddleja (Coulaud 1989) are in conflict with this. It ap­ pears that vestured pits are an unusual feature in the wood of Loganiaceae because in most families the character is thought to be absent or present in all members. As already stated above, wood anatomical features of the Potalieae do not support their inclusion in the Gentianaceae. Anthocleista, Fagraea and Potalia have the fol­ lowing characters in common in which they differ from woody Gentianaceae: rather wide intervessel pits, almost exclusively uniseriate rays, mainly composed of upright/ square ray cells, and abundant banded parenchyma (Mennega 1980; Coulaud 1989).

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Moreover, identical crystals were found in these two genera and not in the gentiana­ ceous wood sampies. Other records of the occurrence of crystals in wood of Logania­ ceae are from Coclaell (1941: Strychnos), Chattaway (1956: Strychnos and Nuxia), Mennega (1980: crystal sand in Neuburgia and rhombic crystals in Strychnos), and Coulaud (1989: Strychnos, Bonyunia and Neuburgia).

ACKNOWLEDGEMENTS

The director of the National Botanic Garden of Belgium (BR) is acknow1edged for the permission to execute anatomical studies on herbarium material. This research was supported by grants from the Fund for Scientific Research - Flanders (F.W.O., Belgium): project number 2.0038.91 (scan­ ning electron microscope) and project number G.0143.95 (general research).

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