Wood Anatomy of Myrciaria, Neomitranthes, Plinia and Siphoneugena Species (Myrteae, Myrtaceae)

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Santos IAWAet al. –Journal Wood anatomy 34 (3), 2013:of selected 313–323 Myrtaceae 313

WOOD ANATOMY OF MYRCIARIA, NEOMITRANTHES, PLINIA AND SIPHONEUGENA SPECIES (MYRTEAE, MYRTACEAE)

Gabriel U.C.A. Santos1,*, Cátia H. Callado2, Marcelo da Costa Souza3 and Cecilia G. Costa4 1 Colégio Pedro II, CSCII, Campo de São Cristóvão 177, 20921-440 São Cristóvão, Rio de Janeiro, RJ, Brazil 2Universidade do Estado do Rio de Janeiro, Departamento de Biologia Vegetal, Instituto de Biologia Roberto Alcantara Gomes, Rua São Francisco Xavier 524, PHLC - sala 224, 20550-900 Maracanã, Rio de Janeiro, RJ, Brazil 3Museu Nacional / UFRJ, Departamento de Botânica, Quinta da Boa Vista, 20940-040 São Cristóvão, Rio de Janeiro, RJ, Brazil 4Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Laboratório de Botânica Estrutural, Rua Pacheco Leão 915, 22460-030 Jardim Botânico, Rio de Janeiro, RJ, Brazil *Corresponding author; e-mail: [email protected]

abstract Myrciaria, Neomitranthes, Plinia and Siphoneugena are closely related genera whose circumscriptions are controversial. The distinctions between Myrciaria vs. Plinia, and Neomitranthes vs. Siphoneugena, have been based on a few fruit characters. The wood anatomy of 24 species of these genera was examined to determine if wood anatomical features could help delimit the genera. It was determined the four genera cannot reliably be separated by wood anatomy alone. Characteristics seen in all four genera are: growth rings usually poorly-defined; diffuse porous; exclusively solitary vessels, usually circular to oval in outline; simple perforation plates; vessel-ray pits alternate and distinctly bordered; fibers with distinctly bordered pits in radial and tangential walls, usually very thick- walled; vasicentric tracheids typically absent; scanty paratracheal parenchyma, sometimes unilateral, and diffuse to diffuse-in-aggregates; chambered crystal- liferous axial parenchyma in many species, usually both prismatic and smaller crystals; rays 1–4-seriate, uniseriate rays composed of upright/square cells, multiseriate rays with procumbent body cells and 1 to many marginal rows of upright/square cells; disjunctive ray parenchyma cells usually present. Key words: Comparative wood anatomy, generic boundaries, South American Myrteae, Plinia group.

INTRODUCTION

Myrtaceae has 132 genera and 5671 species, of which 49 genera and c. 2500 species are in the tribe Myrteae (Lucas et al. 2007). The Myrteae comprises trees or occasionally shrubs and has a Pantropical distribution (Lucas et al. 2007), with high species diversity occurring along the eastern coast of Brazil, the Guayana Highlands and the Caribbean (McVaugh 1968). Although the family is considered well-delimited and

Downloaded from Brill.com10/08/2021 06:52:18AM via free access 314 IAWA Journal 34 (3), 2013 easily recognizable in the field, the circumscription of its genera and species has been debated since the 19th century (Landrum & Kawasaki 1997; Lucas et al. 2005). One of the reasons for this confusion in generic boundaries is that many genera are distinguished by a single or relatively few, often cryptic characters, such as the degree of fusion in the calyx and in the embryo (Landrum & Kawasaki 1997; Salywon & Landrum 2007). Generic boundaries within Myrteae have attracted attention in past decades. Lucas et al. (2005, 2007) carried out molecular phylogenetic studies to clarify relationships within the tribe. They concluded that the traditional three subtribe system based on embryology and proposed by Berg (1855–56, 1857–59) is artificial, with subtribes Myr- ciinae and Eugeniinae being polyphyletic. The Plinia group is one of the well-supported monophyletic informal groups proposed by Lucas et al. (2007). It comprises four genera: Myrciaria, Neomitranthes, Plinia and Siphoneugena. Myrciaria O. Berg has 25 species (Govaerts et al. 2012) that occur from northern Argentina to Mexico and the Caribbean (Landrum & Kawasaki 1997). It is closely related to Plinia L., a genus dis- tributed from Brazil and Peru to the West Indies and Cuba (Barrie 2004). The distinction between Myrciaria and Plinia is controversial, since only the persistence of the calyx in the fruit distinguishes them, which has led some authors (e.g. Legrand & Klein 1978) to consider Plinia species as Myrciaria. Plinia is considered artificial by some authors (e.g. Landrum & Kawasaki 1997); Barrie (2004) states that the range of the esti- mates of the number of species of Plinia (6–40 species) indicates its poor generic limits. Another indication is the controversial placement of species known as “jaboticabas”, a small group of eight species treated either as Myrciaria (e.g. Landrum & Kawasaki 1997) or Plinia (e.g. Govaerts et al. 2012). Those species will be treated here as Plinia. Neomitranthes Kausel ex D. Legrand comprises 14 species from the Brazilian Atlantic Domain (Souza 2009). It is closely related to Siphoneugena O.Berg, a small genus of 9 species ranging from southern Brazil to the Antilles (Sobral & Proença 2006). The distinction between them is also obscure, the principal difference being hypanthium morphology (circumscissile below the staminal ring in Siphoneugena and above in Neomitranthes) (Landrum & Kawasaki 1997). Due to these controversies about the generic limits within the Plinia group, the present study was undertaken to determine whether wood anatomical characters might be useful for distinguishing the genera.

MATERIALS AND METHODS

Wood samples of 19 species were obtained either from field expeditions or from various institutional wood collections, data on five species were obtained from the literature (Table 1). In the field, all samples were taken at breast height, either cut with a saw or sampled with an increment borer. Transverse, radial and tangential sections 20–25 µm thick were cut using a sliding microtome. Sections were bleached in 2–3% sodium hypochlorite, stained in 1% Astra blue and then in 1% safranin in 50% ethanol, dehydrated, and mounted in synthetic resin. Macerations were prepared using Frank- lin’s method, as modified by Kraus and Arduin (1997). Terminology, definitions and measurements follow recommendations of an IAWA Committee (1989). Measurements were taken using Image Pro-Plus 4.0.

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Table 1. Specimens details.

Genus / Species Registration number Specimen origin

Myrciaria O. Berg M. disticha O. Berg RBw 8638 Linhares (ES), Brazil RBw 9022 Santa Teresa (ES), Brazil M. ferruginea O. Berg BOTw 854, BCTw 7939 Linhares (ES), Brazil M. floribunda(H. West ex Willd.) RBw 8598, RBw 8599, Quissamã (RJ), Brazil O. Berg RBw 8604 M. glazioviana (Kiaersk.) G.M. Barroso RBw 8755, RBw 8966, Rio de Janeiro (RJ), Brazil ex Sobral RBw 8989 M. guaquiea (Kiaersk.) Mattos & RBw 8754 Niterói (RJ), Brazil Legrand M. strigipes O. Berg BOTw 853 Linhares (ES), Brazil RBw 9024, RBw 9025 São Mateus (ES), Brazil Neomitranthes D. Legrand N. cordifolia (D. Legrand) D. Legrand RBw 8262 Sombrio (SC), Brazil N. glomerata (D. Legrand) D. Legrand RBw 8263 Palhoça (SC), Brazil N. obscura (DC.) N. Silveira RBw 8402 Rio de Janeiro (RJ), Brazil RBw 9023 Santa Teresa (ES), Brazil N. sp. (species unassigned) RBw 8639 Linhares (ES), Brazil Plinia Plum. ex L. P. cauliflora(Mart.) Kausel RBw 8751 Rio de Janeiro (RJ), Brazil P. costata Amsh. Tw 37774, Tw 37797 Nickerie, Suriname P. edulis (Vell.) Sobral RBw 8721, RBw 8749 Rio de Janeiro (RJ), Brazil P. ilhensis G.M. Barroso RBw 8753 Niterói (RJ), Brazil P. oblongata (Mattos) Mattos RBw 8981, RBw 8982 Santa Teresa (ES), Brazil P. peruviana (Poir.) Govaerts RBw 8722, RBw 8723 Rio de Janeiro (RJ), Brazil P. renatiana G.M. Barroso & RBw 9020, RBw 9021 Santa Teresa (ES), Brazil A. L. Peixoto BCTw 18482 Linhares (ES), Brazil Siphoneugena O. Berg S. kiaerskoviana (Burret) Kausel RBw 7307, RBw 7538 Nova Friburgo (RJ), Brazil S. reitzii D. Legrand RBw 8283 São Joaquim (SC), Brazil

RESULTS We found that wood anatomy of the four genera is quite homogenous and so present a general description for them. Summaries of the qualitative and quantitative features that varied among species are in Tables 2 and 3, respectively. There is the possibility that some individual species can be recognized by their wood anatomy, but more samples need to be studied to verify this. Growth rings – Usually poorly marked, rarely absent, described as distinct in P. martinellii (Barros & Callado 1997) and P. rivularis (Santos 2012). Usually marked by radially-flattened, thick-walled fibers and lower frequency of axial parenchyma; some species also show lower frequency of vessels (Fig. 1A, D).

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Table 2. Summary of qualitative features that varied among Myrciaria, Neomitranthes, Plinia and Siphoneugena woods. Data are from direct observation, except when noted (1Santos 2012; 2Marchori & Muñiz 1987; 3Barros & Callado 1997; 4Paula et al. 2000). SVO = solitary vessel outline (A = angular, CO = circular to oval); DHV = deposits in heartwood vessels (C = common, O = occasional, A = absent/not observed); FWT = fiber wall thickness (T = thin to thick, VT = very thick); RMP = rays with multiseriate portions as wide as uniseriate portions (Y = yes, N = no); crystals (PC = in chambered axial parenchyma cells, E = crystals in enlarged axial parenchyma cells, T = two sizes of crystals in the same chambered cell, A = absent/not observed); vitreous silica (P = present in axial parenchyma cells; A = absent/not observed); * = unknown.

Species Samples SVO DHV FWT Ray width RMP Crystals Vitreous silica

M. cuspidata1 1 CO O t 1; 2 O A A M. disticha 2 CO C VT 1; 2 O t A M. ferruginea 2 CO O VT 1; 2 N A A M. floribunda 3 CO C t 1; 2–3 N A A M. glazioviana 3 CO A t 1; 2 N A A M. guaquiea 2 CO A VT 1; 2 N A A M. strigipes 2 CO A VT 1; 2 Y A A M. tenella2 2 CO A t 1; 2–3 N A A

N. cordifolia 1 CO-A A VT 1; 2 O PC A N. glomerata 1 CO A VT 1; 2 O PC A N. obscura 2 CO A VT 1; 2 N PC A N. sp 1 CO A VT 1; 2 O t A

P. cauliflora 1 CO-A A t 1; 2 N t A P. costata 2 CO A VT 1; 2 N A A P. edulis 2 CO A VT 1; 2–3 N A A P. ilhensis 1 CO O VT 1 Y E A P. martinellii3 2 CO A t 1; 2–3 O PC P P. oblongata 2 CO-A A t 1; 2 O PC A P. peruviana 2 CO-A O t 1; 2 O t A P. renatiana 3 CO O VT 1; 3–4 N A A P. rivularis1 1 CO A VT 1; 3 N t A

S. densiflora4 1 * A t 1; 2–3 O A A S. kiaerskoviana 2 CO A t/VT 1; 2–3 N t A S. reitzii 1 A A VT 1; 3–4 N t A

Vessels – All species diffuse-porous (Fig. 1A–E). Vessels predominantly solitary (> 90%), only rarely tending to a diagonal to radial arrangement. Vessel outline mostly circular to oval, in some species a tendency to an angular outline (Table 2). Perforation plates simple. Intervessel pits rarely observed (since most species have all or almost all vessels solitary), alternate; vessel-ray pits similar to intervessel pits (Fig. 1G–I); vesturing, assumed to be present as is characteristic of the Myrtaceae, not obvious with light microscopy, except in M. tenella and P. martinellii. A few species with occasional

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* * -40-61 * 8-16.3-24 Ray width 6.5-10.4-14.8 9.5-18.3-32.4 9.5-27.7-53.4 8.3-15.7-21.3 9.5-15.7-22.2 9.5-18.4-29.5 9.3-15.5-23.3 6.3-13.0-22.5 11.3-15.5-23.2 11.8-30.6-42.2 20.5-26.4-37.4 12.7-16.9-22.2 14.8-19.9-26.0 13.9-32.4-53.3 17.6-25.7-35.5 13.9-19.7-28.9 10.2-15.2-20.3 20.0-27.7-40.4 12.6-17.3-22.5 10.5-16.1-24.2

m; Flu = fiber lumen µ Ray height 57-267-609 92-183-283 40-241-520 50-239-700 42-203-767 117-235-439 115-238-376 117-245-678 117-319-786 167-368-646 152-276-533 129-258-559 101-383-718 138-251-457 161-282-538 138-282-668 491-520-549 120-323-771 168-403-637 123-227-324 205-364-696 174-373-839 94.3-210-331 142-421-1047 2000). All values represent

et al. *

RF 5-15- 7-11-16 9-13-16 5-15-21 9-14-18 9-13-16 9-16-19 9-17-27 7-12-18 5-10-13 11-14-19 16-19-23 14-19-24 10-13-16 13-19-24 15-21-26 12-18-21 13-19-27 19-21-25 10-14-17 15-18-22 26-29-32 23-28-33 16-21-277 Paula 4

* 4-6 5-8 6-8 3-6 4-6 3-9 4-6 3-7 4-6 5-8 4-8 3-8 4-6 4-7 3-4 4-6 3-9 3-5 3-8 3-7 7-11 5-14 4-14 APS

* * * * FLu m); fiber length, fiber diameter = 2-6.1-24 µ 1.3-3.1-5.7 3.2-6.1-8.6 1.4-2.7-4.8 1.8-3.6-9.5 1.7-3.7-5.3 3.3-4.8-7.5 1.6-4.2-8.5 2.4-4.8-6.5 2.2-4.5-7.3 2.1-4.2-8.2 1.3-2.4-7.6 3.7-6.0-9.8 2.4-5.5-9.8 1.5-2.7-5.1 2.2-3.1-5.2 1.6-4.2-8.5 3.4-5.8-8.1 2.2-3.5-7.9 2.2-4.1-7.7

* woods. Barros & Callado 1997; 3 -17.0- * 14-22.1-95 10-13-17.5 8.7-11.4-15 7.4-13.8-19.8 Fiber diameter 11.2-16.8-22.8 11.4-16.6-22.7 11.7-16.2-20.4 11.8-18.6-27.6 11.6-16.8-22.2 11.2-15.9-20.9 11.3-15.9-20.0 11.8-16.0-20.7 11.4-16.2-20.6 14.4-17.8-22.4 12.6-19.7-27.2 12.0-18.3-25.0 15.4-19.6-23.8 13.7-16.5-20.8 12.0-16.2-21.1 12.7-19.5-26.5 15.6-18.3-20.3 14.4-19.2-27.6 16.2-18.8-22.5

= unknown. Sp = number VFr of = samples; vessel frequency (vessels/mm²);

* * Siphoneugena = vessel wall thickness ( T and Fiber length 1110-1320- 650-937-1190 534-919-1654 665-972-1330 645-974-1421 524-863-1249 600-953-1470 801-965-1316 520-799-1314 851-1104-1598 749-1130-1419 691-1121-1382 741-1108-1415 630-1013-1439 849-1532-2047 578-1023-1438 774-1050-1418 765-1271-1806 729-1012-1406 759-1006-1314 980-1316-1550 856-1277-1704 810-1012-1360 1109-1272-1645 m); VW

µ Marchori & Muñiz 1987;

2 T

* VW 2-2,9-4 2-2.9-4 2.1-3.1-4.8 2.3-3.6-4.7 1.4-2.4-3.9 1.9-3.0-4.3 1.8-2.8-3.8 3.6-5.3-8.3 1.6-2.5-3.4 1.9-3.3-4.7 2.3-3.1-6.0 2.5-3.3-4.8 2.0-3.5-4.7 2.4-3.6-5.9 1.3-2.1-2.7 3.4-5.0-6.7 2.1-3.1-3.8 3.1-4.2-6.6 1.9-2.6-4.7 3.1-3.7-4.1 2.1-3.5-5.8 2.0-3.0-4.3 1.3-1.6-2.1

Santos 2012; 1

D T V 15-29-40 81-93-103 32.5-48-70 30-59.8-140 17.5-29.5-36 19.0-36.9-51.3 24.1-29.1-33.3 20.7-31.9-42.2 16.7-39.6-58.7 31.4-72.8-95.4 30.0-65.0-95.3 19.9-30.5-56.5 24.2-41.2-56.3 22.7-32.3-41.9 17.3-35.9-48.0 27.4-49.4-81.3 23.2-30.0-44.5 23.7-47.8-66.8 21.7-50.2-117.0 63.4-77.9-112.5 47.4-89.9-141.6 46.5-72.9-105.8 49.5-130.0-235.4 61.4-126.1-177.1

D = vessel tangential diameter (

Myrciaria, Neomitranthes, Plinia Myrciaria, T VEL m); V 211-533-833 350-514-730 216-476-662 390-602-875 338-567-862 540-674-890 340-515-750 288-512-724 365-541-758 370-640-902 271-431-657 310-535-888 403-645-951 481-602-751 193-473-781 250-346-400 330-535-680 270-439-620 316-679-953 306-438-821 270-468-670 126-656-1056 288-582-1055 431-755-1201 µ

VFr 0-5-11 7-13-17 21-28-35 26-38-54 34-50-95 25-27-36 24-38-49 13-15-18 16-29-54 85-95-112 62-85-123 75-89-100 20-61-123 63-114-169 88-107-135 81-131-181 76-101-139 110-152-238 107-118-139 112-177-240 198-237-275 136-159-184 160-171-208 198-233-264

1 2 1 2 1 3 2 2 1 3 2 3 2 2 2 1 2 1 1 1 2 2 1 2 Sp

1 4

sp m); APS = axial parenchyma strand (in number of cells); RF ray frequency (rays/mm);m); ray height, width = able 3. Quantitative features of µ P. martinellii P. P. ilhensis P. M. tenella P. edulis P. P. cauliflora P. costata P. S. reitzii M. glazioviana M. guaquiea M. strigipes N. P. renatiana P. rivularis P. S. kiaerskoviana S. densiflora M. floribunda N. obscura P. peruviana P. M. ferruginea N. glomerata P. oblongata P. T Data are from direct observation, except when noted ( Species M. cuspidata M. disticha minimum-mean-maximum, except for axial parenchyma strand (minimum-maximum). VEL = vessel element length ( N. cordifolia (

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Figure 1. For legends, see page 320.

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Figure 2. For legends, see page 320.

Downloaded from Brill.com10/08/2021 06:52:18AM via free access 320 IAWA Journal 34 (3), 2013 yellow to orange gum-like deposits in their vessels, abundant only in M. disticha and M. floribunda. Vessel frequency (vessels/mm2) 5 (P. renatiana) to 237 (P. oblongata), > 100 in many species. Mean tangential diameters from 29.1 µm (P. cauliflora) to 130.0 µm (S. kiaerskoviana), most species < 50 µm. Mean vessel element lengths 346 µm (S. densiflora) to 755 µm (P. martinellii) (Table 3). Fibers – All species with fiber-tracheids with distinctly bordered pits in both radial and tangential walls, in most species very thick-walled (Fig. 1A–C, E–F). Tracheids reported only in M. cuspidata and P. rivularis (Santos 2012). Average fiber length typically > 1000 µm, ranging from 799 (N. cordifolia) to 1532 (P. edulis) (Table 3). Axial parenchyma – All species with scanty paratracheal parenchyma, sometimes in a one-layered cap of unilateral paratracheal parenchyma (Fig. 1B–C). Apotracheal parenchyma diffuse to diffuse-in-aggregates (Fig. 1A–F), occasionally in narrow bands (1B). Strands of 3–14 cells (Table 3). Rays – All species with two distinct populations of rays as defined by cellular com- position (Fig. 2A-D): a) uniseriate rays, composed only of square/upright cells; and b) 1–4 cell wide rays comprised of procumbent body cells and one to several marginal rows of square/upright cells. Disjunctive ray parenchyma cells present. Rays typically numerous, ranging from 10 (P. martinellii) to 28 rays/mm (M. tenella) (Table 3). Crystals – Present in most species (Table 2). In some species, only one size of prismatic crystals in chambered axial parenchyma cells; in many species, two sizes of crystals in the same cell (prismatic plus smaller crystals, Fig. 2F, G). This latter feature difficult to assess because smaller crystals might be cryptically present among prismatic (larger) crystals. In P. ilhensis crystals occur in slightly inflated parenchyma cells (Fig. 2H). Silica – Vitreous silica in axial parenchyma cells reported only in P. martinellii (Santos 2012).

Figure 1. – A–F: Transverse sections of Myrciaria and Plinia woods. Diffuse porosity, solitary vessels, very thick-walled fibers, diffuse to diffuse-in-aggregates apotracheal parenchyma, scanty, sometimes unilateral paratracheal parenchyma. – A: M. glazioviana. Growth ring boundaries marked by radially-flattened fibers (arrows). – B: M. guaquiea. – C: M. strigipes. Unilateral paratracheal parenchyma (arrow). – D: P. oblongata. – E: P. edulis. – F: P. renatiana. Indistinct growth ring boundary marked by a single row of radially-flattened fibers (arrow). – G–I: Radial sections. Alternate vessel-ray pits. – G: M. disticha. – H: M. ferruginea. – I: M. guaquiea. — Scale bars: A, E = 210 µm; B, C, D = 90 µm; F = 80 µm; G, H, I = 30 µm.

Figure 2. Longitudinal sections of Myrciaria, Plinia and Siphoneugena woods. – A–E: Tan- gential sections. Uniseriate rays composed of upright/square cells (thick arrows), 1–4-seriate rays composed of procumbent cells in the body and marginal rows of upright/square cells (thin arrows). – A: P. ilhensis. Exclusively uniseriate rays. – B: M. disticha. Uniseriate and biseriate rays. – C: P. edulis. Uniseriate and 2–3-seriate rays. – D: P. renatiana. Uniseriate rays and 3–4-seriate rays. – E: Radial section of P. renatiana. Rays composed of procumbent cells in the body and marginal rows of upright /square cells. – F–H: Crystals. – F: P. peruviana. – G: S. kiaerskoviana. – H: P. ilhensis. — Scale bars: A = 55 µm; B, C = 160 µm; D, E = 120 µm; F = 40 µm; G = 20 µm; H = 90 µm.

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DISCUSSION

All aforementioned features are consistent with previous descriptions of Myrtaceae woods (e.g. Metcalfe & Chalk 1950; Ingle & Dadswell 1953), except for some slight differences. First, Metcalfe and Chalk (1950) indicate that vasicentric tracheids are a typical feature of the family, but these were only observed in two species, M. cuspidata and P. rivularis (Santos 2012). Their absence, however, might not be uncommon in tribe Myrteae – e.g. Marques (2010) reported vasicentric tracheids in only 3 out of 8 Eugenia species studied. The occurrence of two populations of rays with distinct cell compositions, as seen in the species we studied, is not a feature described as such in Metcalfe and Chalk’s (1950) family description. This feature has been described before in Myrtaceae, e.g., Wagemann (1948), Ingle & Dadswell (1953), Ragonese (1977) and Barros et al. (2001). This character is common in the tribe Myrteae (Santos et al., in preparation). Although this feature was not recognized in Siphoneugena densiflora by Paula et al. (2000), it is clearly seen in their figure. We also observed it inP. martinellii (in slides from RBw), although Barros and Callado (1997) did not describe it; our observations of this feature also differ from Record & Hess (1943) for Myrciaria. Among the species studied, species complexes have been recognized on the basis of similarities in external morphology. Species in these complexes also have similar wood anatomy (Table 2 & 3). Myrciaria guaquiea, M. strigipes and M. glazioviana are in one complex and they have similar anatomy. The “jaboticabas” species analyzed (P. cauliflora, P. oblongata and P. peruviana) share similar features (narrow and very numerous vessels, with angular outline; 1–2-seriate rays). On the other hand, N. cordifolia, a species not considered part of this “jaboticabas” complex, is quite similar wood anatomically. Some wood characters may be diagnostic for some of the species: silica was only observed in P. martinellii; exclusively uniseriate rays and crystals in somewhat enlarged parenchyma cells was only observed in P. ilhensis (although only one sample of P. ilhensis was analyzed). However, these diagnostic features are few. Most of the qualitative features that varied among species are environmentally influenced to some degree (e.g. growth ring boundary distinctiveness – Evert 2006), subjective (e.g. rays with multiseriate portions as wide as uniseriate portions) or have some probability to be overlooked (e.g. mineral inclusions). Due to this homogeneity in wood anatomy, it is not possible to use wood characters to distinguish Myrciaria from Plinia, or Neomitranthes from Siphoneugena. In fact, it is not possible to separate any of the four genera. This homogeneity is another indication of their close relationship, as is the similarity in plant morphology. A similar situation for four genera of the subtribe Myrciinae was found by Dias-Leme et al. (1995), who concluded that wood anatomical characters could not segregate Calyptranthes, Gomide- sia, Marlierea and Myrcia, The wood anatomical data supported merging these genera into a single genus, as proposed earlier by McVaugh (1968). A recent molecular-based phylogeny (Lucas et al. 2011) supports those views, and inclusion of these genera in Myrcia is being proposed (Lucas & Sobral 2011).

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On the other hand, homogeneity may indicate that wood anatomy provides limited useful information for the systematics of the Plinia group, or even Myrteae. An analysis of wood anatomical data of other Myrtean genera described in literature – e.g. some Eugenia (Détienne & Jacquet 1993; Marques 2010) and some Myrcia (Barros et al. 2001) – shows that their wood structure is often very similar to that of Myrciaria, Neomitranthes, Plinia and Siphoneugena. Santos (2012) studied the wood anatomy of 26 species of southern Brazilian Myrtaceae and did not find any characters that could separate genera (except for Myrceugenia, based on pit morphology). Lucas et al. (2007), based on unpublished wood anatomical data, state that the type of perforation plates is possibly the only taxonomically useful character for distinguishing Myrteae genera. They found that most of Myrtean genera have exclusively simple perforation plates, except for five genera in which some scalariform perforation plates occur (Luma, Myr- ceugenia, Myrteola, Ugni and Neomyrtus), and two taxa with mixed simple, reticulate or scalariform perforation plates (Lophomyrtus and Blepharocalyx cruckshanksii) (Lucas et al. 2007). Schmid and Baas (1984) recorded scalariform perforations in 40 species belonging to seven genera in the family as a whole, six of them Myrtoideae and Tepualia belonging to the Leptospermoideae. A comprehensive wood anatomical survey of Myrteae is needed to clarify the sys- tematic importance of its wood anatomy, since the wood structure of many groups is poorly known. It seems clear, however, that within the Plinia group wood anatomy alone does not aid in delimiting genera.

ACKNOWLEDGEMENTS

The authors express their gratitude to FAPERJ, CNPq and CAPES for grants and fellowships; MN/ UFRJ and MBML for field expeditions; JBRJ and UERJ for laboratory structure; ICMBio for research licence; to Maria J. Miranda (BCTw), Carmen Marcati (BOTw), Neusa Tamaio (RBw), and Hans Beeckman (Tw) for wood samples; J.A.T. Glória (UERJ) and F. Santos (JBRJ) for technical support; and the many colleagues that helped in field expeditions, especially A.A.M. de Barros (UERJ), A.G. Oliveira and L.F.T. de Menezes (UFES), F.Z. Saiter (IFES), A.Z. Monico (ESFA), M.D.M. Vianna Filho (MN/UFRJ) and A.F.P. Machado (UEFS).

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