IAWA Journal, Vol. 30 (3), 2009: 247–276 WOOD ANATOMY OF CAESALPINIA s.s., COULTERIA, ERYTHROSTEMON, GUILANDINA, LIBIDIBIA, MEZONEURON, POINCIANELLA, POMARIA AND TARA (LEGUMINOSAE, CAESALPINIOIDEAE, CAESALPINIEAE) Peter Gasson, Kate Warner and Gwilym Lewis Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, United Kingdom SUMMARY Caesalpinia s.l. traditionally comprised c. 140 species in the New and Old World tropics, and contained a maximum of 25 generic synonyms. The genus in its broad- est sense has been shown to be polyphyletic in molecular studies, and most species have now been assigned to reinstated segregate genera: Caesalpinia s.s. (c. 25 spp.), Coulteria (10 spp.), Erythrostemon (13 spp.), Guilandina (c. 7 spp.), Libidibia (8 spp.), Mezoneuron (c. 26 spp.), Poincianella (c. 35 spp.), Pomaria (16 spp.) and Tara (3 spp.). About 15 Asian taxa remain unassigned pending more data, especially DNA sequences. In this paper we describe the wood anatomy of these nine segregate genera, outlining the features that consistently help define some of them. We have examined the wood of 27 species representing all the woody segregate genera and found wood descriptions of three more species in the literature. Most species lack well defined growth rings, vessels are solitary and in radial multiples, intervessel pitting is alternate and vestured, fibres are mainly non-septate, axial parenchyma is aliform to confluent and irregularly storied, and the rays are mainly 1–2-seriate, mostly non-storied, and of varying height. Prismatic crystals are in chambered axial parenchyma cells in all except Erythrostemon gilliesii (Hook.) Link, and in ray cells in many species. Libidibia is well defined, with storied axial parenchyma, narrow short storied homocellular rays and lacking crystals in ray cells. Tara is also well defined with non-storied heterocellular rays and some ray cells containing crystals. The other genera are less consistent in wood characters. In Caesalpinia s.s. the rays are not storied, and most species lack crystals in ray cells. Coulteria has some species with storied rays and all have homocellular rays and crystals in ray cells. Poincianella is particularly poorly defined from a wood anatomical point of view, perhaps indicating that it can be further segregated. A few Poincianella species have septate fibres, which are otherwise seen only inLibidibia corymbosa. Mezoneuron has non-storied, heterocellular rays. The two species of Guilandina we examined have wide vessels and heterocellular rays containing crystals. Only two species of Erythrostemon were examined and E. gilliesii was unusual in having ring porous wood and very wide rays (but the sample was cultivated at Kew, and we do not know its porosity in its native range). Caesalpinia decapetala (Roth) Alston (originally described as Reichardia decapetala Roth) and Caesalpinia sappan L. from the Old World have not been reassigned to a segregate genus. Pomaria is mainly herbaceous and we have included some information on it. Key words: Caesalpinia s.s., Coulteria, Erythrostemon, Guilandina, Libidibia, Mezoneuron, Poincianella, Tara, Pomaria, wood anatomy. Downloaded from Brill.com10/11/2021 11:10:06AM via free access 248 IAWA Journal, Vol. 30 (3), 2009 INTRODUCTION Caesalpinia s.l. traditionally comprised c. 140 species in the New and Old World trop- ics, and contained 25 generic synonyms (Lewis 2005). The genus in its broadest sense has been shown to be polyphyletic in morphological and molecular studies (Lewis & Schrire 1995; Simpson & Miao 1997; Lewis 1998; Simpson 1998, 1999; Simpson & Lewis 2003, Simpson et al. 2003), and most species have now been assigned to rein- stated segregate genera, whose names and/or status differ from the group names used in Lewis (1998) as follows: Caesalpinia s.s. (c. 25 spp.), Coulteria (10 spp., Brasilettia group in Lewis (1998)), Erythrostemon (13 spp., part of Erythrostemon/Poincianella group in Lewis (1998)), Guilandina (c. 7 spp., subgenus Guilandina), Libidibia (8 spp., Libidibia group), Mezoneuron (c. 26 spp, subgenus Mezoneuron), Poincianella (c. 35 spp., part of Erythrostemon/Poincianella group), Tara (3 spp., Russellodendron group in Lewis (1998)). About 15 Asian taxa remain unassigned pending further analysis, especially of molecular data. Pomaria was once largely included in Hoffmannseggia but is now considered more closely related to Caesalpinia s.l. based on molecular studies by Simpson et al. (2003). Some species of Caesalpinia s.l. (e.g. Poincianella pannosa and P. exostemma) have considerable morphological variation in their foliage, leaflet size, shape and indumentum, which has led to a proliferation of species names now included in synonymy. In this paper we describe the wood anatomy of the genus in its broadest sense, and outline the features (if any) that consistently define each segregate genus. Our major aim was to ascertain how closely the wood anatomy reflects the reclassification ofCaesalpinia s.l. into putatively monophyletic segregate genera. The wood anatomy of Caesalpinia s.l. is not simply of academic interest. Several species are well-known and of considerable economic importance. Caesalpinia echi- nata (currently tentatively placed in the Poincianella-Erythrostemon alliance, although proving to be molecularly distinct), locally known as pau-brasil (Brazil wood) and the wood after which the country Brazil was named, is an emblematic tree of the Atlantic forests of coastal Brazil and is the only wood used to make professional high-quality violin bows. There is a considerable literature on this species, which has recently been listed under Appendix 2 of CITES regulations as a timber not to be internationally traded. Another well-known species, Caesalpinia pulcherrima L. from Mexico and Guatemala, is widely cultivated in warm climates as an attractive ornamental and has various medicinal properties. Caesalpinia (Poincianella) pyramidalis Tul. is valued in the caatinga region of northeast Brazil as one of several species used for firewood and charcoal production, and a project is currently being carried out by Kew and the Associaçao Plantas do Nordeste (APNE) to ascertain the best management methods (coppicing or pollarding in the dry or wet season) to produce high quality fuel wood. It would be premature to publish all the new combinations necessary in the reinstated genera, mainly because there is still some doubt as to the correct generic allocation of some species, e.g. Caesalpinia echinata Lam. from Brazil, and 15 Old World taxa, mainly from Asia. These taxa cannot be placed with confidence until a comprehensive molecular phylogeny of Caesalpinia s.l. has been completed. Our observations on wood anatomy provide additional data testing species placement and generic relationships. Downloaded from Brill.com10/11/2021 11:10:06AM via free access Gasson, Warner & Lewis — Wood anatomy of Caesalpinia sensu lato 249 In this paper we use binomials in the segregate genera where these already exist in the literature or Caesalpinia binomials with their associated segregate genus in brackets where new combinations are still required in the segregate. Gasson et al. (2003) found some variation in the wood anatomy of Caesalpinia s.l. in their survey of Caesalpinioideae. They identified several wood characters which can be used for distinguishing between species and genera in the subfamily: storey- ing of vessels, axial parenchyma and rays, ray size and cell composition, presence or absence of prismatic crystals in ray cells, vestured intervessel pits, intervessel pit size, axial parenchyma patterns, presence or absence of septate fibres, fibre wall thickness, presence or absence of silica bodies and axial canals. The last two characters, silica bodies and axial canals, which are useful diagnostic features in some genera of Caesal- pinioideae are not found in Caesalpinia s.l. This study further develops the analysis of wood characters in Caesalpinia s.l. and shows that some characters support generic segregation, some do not, and some are equivocal. MATERIALS AND METHODS Caesalpinia species covering nine recently reinstated segregate genera (Lewis 2005) and two unplaced Old World species were examined in detail, and a brief description of Pomaria is also included. We obtained data on c. 46 species by direct observation (see Table 1 and the Appendix for details of the specimens) and on three additional species from the literature (see Table 1). Specimens were sectioned in their transverse, tangential and radial planes at 20–40 µm thick using a Reichert sliding microtome and stained in 1% Alcian blue and 1% Safranin in 50% ethanol. Sections were then taken through a dehydration process using ethanol, cleared in histoclear and the three planes were mounted onto microscope slides using Euparal. Information on habit (tree, shrub, liana etc.), habitat and major uses is taken from Lewis (2005). The majority of specimens were from branches and therefore juvenile, and the Appendix indicates the radius of each sample and which ones we consider to be mature. The wood anatomical characters, vessel diameter and intervessel pit size classes fol- low the categories given in Wheeler et al. (1989), and Table 1 is in a similar format to that for the Caesalpinioideae in Gasson et al. (2003). The Appendix lists the specimens examined. WOOD ANATOMY A general description of the wood anatomy of Caesalpinia s.l. is not given because the genus, as traditionally circumscribed, is polyphyletic. However, a brief summary of similarities and differences