IAWA Journal, Vol. 21 (2), 2000: 213–235 WOOD ANATOMY OF ACALYPHOIDEAE (EUPHORBIACEAE) by W. John Hayden & Sheila M. Hayden Department of Biology, University of Richmond, Richmond, VA, 23173, USA SUMMARY Via LM and SEM, we studied wood structure of 51 genera representing 19 tribes of Acalyphoideae, the largest subfamily of Euphorbiaceae. Many acalyphoid woods possess the following features: growth rings indistinct or weakly defined; pores evenly distributed; simple perfora- tion plates (but admixture of irregular scalariform plates common); al- ternate intervessel pits; vessel-ray pits larger than intervessel pits, circu- lar to elongate and alternate to irregular; thin to moderately thick-walled non-septate fibre-tracheids or libriform wood fibres; parenchyma dis- tribution diffuse, diffuse-in-aggregates, and scanty paratracheal, some- times in thin-tangential bands; heterocellular rays seldom more than 3 cells wide; and prismatic crystals in parenchyma and/or ray cells. Within this syndrome, a number of other wood characters also occur but at lower frequency. For the most part, the unusual features have not proven systematically informative at the tribal level. Presence of lysi- genous radial canals, however, supports recognition of tribe Alchorneae. Wood data do not support the segregation of Peraceae and Pandaceae from subfamily Acalyphoideae. Key words: Acalyphoideae, Euphorbiaceae, Pandaceae, Peraceae, wood anatomy. INTRODUCTION Acalyphoideae is the largest and most complex of the five subfamilies of the Euphorbiaceae. Its diversity can be summarized succinctly via statistics from Websterʼs (1994) classification: 20 tribes, 116 genera, and c. 2,000 species that are found through- out the world but are especially abundant in the tropics. Within the family, Acalyph- oideae consists of those plants that have uniovulate locules but lack the characteristic pollen, latex, and indumentum features that define Crotonoideae and Euphorbioideae (Webster 1994). Thus, Acalyphoideae appears to be a paraphyletic assemblage. In- cluded within the ranks of Acalyphoideae are several genera of uncertain taxonomic placement. For example, Pera has been segregated as family Peraceae (Airy Shaw 1965; Radcliffe-Smith 1987), the genera of tribe Galearieae have been placed in Pandaceae (Cronquist 1981; Radcliffe-Smith 1987; Takhtajan 1997), and Dicoelia has been included in Pandaceae (Webster 1987) or, sometimes, in Euphorbiaceae sub- family Phyllanthoideae (e.g., Pax & Hoffmann 1931; Mennega 1987). Downloaded from Brill.com10/07/2021 08:57:34AM via free access 214 IAWA Journal, Vol. 21 (2), 2000 Approximately 86 percent of acalyphoid genera can be characterized as woody. Although a large number of publications contain some information on wood structure of various members of Acalyphoideae (see Appendix), most of these consider a small number of genera and no general summary of wood anatomical diversity for the sub- family exists. This paper, therefore, attempts to fill this gap based on readily available materials from collections at the Smithsonian Institution (USw) and University of Utrecht (Uw). This paper joins papers on Phyllanthoideae (Mennega 1987), Oldfield- ioideae (Hayden 1994), and Euphorbioideae (Mennega, in preparation) as a contribu- tion towards the elucidation of the anatomy and systematics of Euphorbiaceae. MATERIALS AND METHODS Wood specimens of Acalyphoideae examined here are listed in the Appendix. This also includes a guide to previous wood anatomical literature for each genus. We pre- pared microscope slides from 110 specimens and examined 46 more via slides loaned from USw and Uw. Materials studied thus represent a total of 19 tribes, 51 genera, and 110 species. Wood blocks were rehydrated by boiling in tap water with a few drops of Aerosol OT solution, rinsed, and sectioned on a sledge microtome. Sections were stained in Harrisʼ hematoxylin and counterstained in safranin. Macerations were prepared by treatment in equal parts of 10 percent nitric and 10 percent chromic acids, followed by several rinses in water, staining in safranin, dehydration in tert- butyl alcohol, and clearing in toluene. Photomicrographs were prepared from Kodak Technical Pan film developed in Kodak HC110 developer at dilution F. For study with SEM, wood sections approximately 1 mm thick were cut from air-dried wood blocks, affixed to specimen stubs, sputter-coated with a gold-palladium mixture, and studied with a Hitachi S-2300 SEM. Scanning electron micrographs were prepared from Kodak Tri-X film developed in Kodak HC110 developer at dilution B. RESULTS AND DISCUSSION Wood anatomy of Acalyphoideae Growth rings — Growth rings, when detectable, are weakly defined by variation in fibre wall thickness or, sometimes, by the presence of boundary parenchyma. Vessels — Vessels are evenly distributed radially and, hence, diffuse-porous when growth rings are present. There are two cases of unusual large-scale vessel distribu- tion: in Necepsia vessels are organized in alternating radial files of wood with and wood without vessels (Fig. 1) and, in Podadenia, vessels are organized into radial files separated by broad aggregate rays (Fig. 2). At small scales, vessels are most fre- quently grouped in a mixture of solitary cells or small radial multiples and/or clusters of 2–6 cells (Fig. 1–10, 12). Predominantly solitary vessels were noted in Botryophora (Fig. 3), Cheilosa malayana, Conceveiba guianensis, C. simulata, Megistostigma, Microdesmis, and Omphalea (Fig. 4). Pore outlines are routinely circular to elliptical but distinctly angular in Dicoelia (Fig. 5) and somewhat so in Microdesmis. Perfora- tions on vessel elements are generally simple (Fig. 13). Perforations are exclusively Downloaded from Brill.com10/07/2021 08:57:34AM via free access Hayden & Hayden — Wood anatomy of Acalyphoideae 215 Fig. 1–3. Transverse sections of acalyphoid woods. – 1: Necepsia afzelii, Cooper Y. 13726, vessels grouped in radial files. – 2:Podadenia sp., Krukoff 4074, aggregate ray. – 3: Botryophora geniculata, Boeea 5494, pith flecks. — Scale bars = 500 μm. Downloaded from Brill.com10/07/2021 08:57:34AM via free access 216 IAWA Journal, Vol. 21 (2), 2000 Fig. 4–12. Transverse sections of acalyphoid woods. – 4: Megistostigma malaccense, Boeea 1389, lianous stem with large, solitary vessels and thin-walled fibres. – 5: Dicoelia sp., Boeea 7794, vessels with angular outline. – 6: Caryodendron grandifolium, Krukoff 5553, paren- Downloaded from Brill.com10/07/2021 08:57:34AM via free access Hayden & Hayden — Wood anatomy of Acalyphoideae 217 scalariform in Microdesmis and Panda. In some genera or particular species, simple perforations occur mixed with scalariform and/or irregular perforations; such mixed perforations occur in some species of Acalypha, Adenophaedra, Agrostistachys, Apar- isthmium (Williams 1936), Bernardia tamanduana (Fig. 15), Botryophora, Caryoden- dron grandifolium, Claoxylon (Fig. 16), Cleidion, Cnesmone (Metcalfe & Chalk 1950), Coccoceras (Fig. 14), Conceveiba krukoffii, C. guianensis, Dicoelia, Discoclaoxylon (Normand 1955), Galearia, Macaranga zenkeri, some species of Mallotus (Metcalfe & Chalk 1950), Mareya, Mercurialis (Metcalfe & Chalk 1950), Pogonophora (Metcalfe & Chalk 1950), and Tragia (Metcalfe & Chalk 1950). The frequency of per- forated ray cells in acalyphoid woods and their propensity for perforations of vari- able and irregular form (see below) demand great care in distinguishing perforation features for ordinary vessel elements as opposed to perforated ray cells. Intervessel pits are circular to elliptical or sometimes angular (polygonal) if crowded, alternate (Fig. 18), and most frequently 5–12 μm in vertical diameter; Dechamps (1979) re- ported intervessel pit diameters of 15 μm for Aparisthmium, but our material has a range of 7–10 μm. Vestured pits have been reported for vessels of Galearia and Panda (Forman et al. 1966) and initial observations via light microscopy suggested vesture- like structures in intervessel pits of Bernardia, Clutia, and Ricinus; SEM studies, how- ever, have failed to reveal true vestured pits in any of these woods. In Bernardia and Clutia, spherical wart-like structures located on the surface of the pit cavity are re- sponsible for the pseudovestures observed via LM. Confluent inner apertures were noted on intervessel pits of Adelia ricinella, Alchorneopsis, Conceveiba, Homonoia, and Octospermum. Intervessel pits are notably small (c. 2 μm) in Microdesmis and also in Claoxylon africanum and Homonoia riparia, but pits of other species of the latter two genera are much larger. Vessel-ray pits are circular to elongate and alter- nate to irregular; elongate pits may be oriented horizontally, vertically, or diagonally and they are characteristically larger than the intervessel pits (Fig. 13, 17, 18). Ves- sel elements are notably long in Coccoceras (c. 2 mm), notably short in Clutia (230– 340 μm), and notably wide in the liana, Megistostigma malaccense (up to 390 μm) (Fig. 4). Fibriform vessel elements were observed grouped with larger vessel ele- ments in Dicoelia and Clutia; in C. abyssinica, some fibriform vessel elements bear few-barred scalariform perforations as opposed to the simple perforations in ordinary vessels; in C. kilimandsharica, fibriform vessel elements possess helical thickenings. Otherwise, we observed helical thickenings only in vessels of Mallotus polyadenus and Microdesmis but they have also been reported for Cleidion, Pogonophora, and Trewia (Metcalfe & Chalk 1950); elongate inner apertures