IAWA Journal, Vol. 26 (1), 2005: 1-68 WOOD ANATOMY OF THE SUBFAMILY EUPHORBIOIDEAE A comparison with subfamilies Crotonoideae and Acalyphoideae and the implications for the circumscription of the Euphorbiaceae Alberta M. W. Mennega Nationaal Herbarium Nederland, Utrecht University branch, Heidelberglaan 2, 3584 es Utrecht, The Netherlands SUMMARY The wood anatomy was studied of 82 species from 34 out of 54 genera in the subfamily Euphorbioideae, covering all five tribes recognized in this subfamily. In general the woods show a great deal of similarity. They are charac­ terized by a relative paucity of vessels, often arranged in short to long, dumbbell-shaped or twin, radial multiples, and by medium-sized to large intervessel pits; fibres often have gelatinous walls; parenchyma apotracheal in short, wavy, narrow bands and diffuse-in-aggregates; mostly uni- or only locally biseriate rays, strongly heterocellular (except Hippomane, Hura and Pachystroma). Cell contents, either silica or crystals, or both together, are nearly always present and often useful in distinguishing between genera. Radiallaticifers were noticed in most genera, though they are scarce and difficult to trace. The laticifers are generally not surrounded by special cells, except in some genera of the subtribe Euphorbiinae where radiallaticifers are comparatively frequent and conspicuous. Three ofthe five tribes show a great deal of conformity in their anatomy. Stomatocalyceae, however, stand apart from the rest by the combination of the scarcity of vessels, and mostly biseriate, vertically fused and very tall rays. Within Euphorbieae the subtribe Euphorbiinae shows a greater vari­ ation than average, notably in vessel pitting, the frequent presence of two­ celled parenchyma strands, and in size and frequency of the laticifers. Data from surveys of the two other subfamilies of the uniovulate eu­ phorbs, Acalyphoideae and Crotonoideae are compared and their relation­ ships are discussed. The comparison of Euphorbioideae, Acalyphoideae, and Crotonoideae shows a great anatomical conforrnity with only a marked difference in the presence of laticifers: scarce in Acalyphoideae and Cro­ tonoideae but nearly always present and often frequent in Euphorbioideae. All in all, wood anatomy supports a narrower family concept of Euphor­ biaceae, inc1uding only Acalyphoideae, Crotonoideae, and Euphorbioideae, while exc1uding Phyllanthoideae and Oldfieldioideae, as has recently been advocated by several authors. In Table 2 (p. 6-7), informative features are summarized. Key words: Wood structure, Euphorbioideae, Acalyphoideae, Crotonoi­ deae, crystals, latex tubes, lysigenous cavities, silica. Downloaded from Brill.com10/09/2021 12:24:23AM via free access 2 IAWA Journal, Vol. 26 (1), 2005 INTRODUCTION Ever since Prof. G.L. Webster aroused my interest in the wood structure ofthe diverse family of the Euphorbiaceae, I have been studying its wood anatomy on a worldwide scale, taking his concept of the family as a base (Webster 1975). He recognized five subfamilies: Phyllanthoideae and Oldfieldioideae comprising the biovulate genera, and Acalyphoideae, Crotonoideae, and Euphorbioideae comprising the uniovulate genera. Wood structure proved to be greatly variable in the biovulate subfamilies as appeared from studies ofPhyllanthoideae (Mennega 1987) and Oldfieldioideae (Hayden 1994), in contrast to the more uniform structure of the three uniovulate subfamilies. Of the latter, Acalyphoideae was studied by Hayden and Hayden (2000). Moreover, a wood atlas has been published recently of end-grain photographs at low magnification covering all subfamilies and roughly half of the total number of genera. This atlas is intended to aid hand-lens inspection (Westra & Koek-Noorman 2004). The present contribution completes the wood anatomical picture ofthe Euphorbiaceae by presenting an extensive treatment of the subfamily Euphorbioideae, and an overview of the Crotonoideae. This paper is an amended version of an unpublished contribution presented at the International conference on the Systematics of the Euphorbiaceae at the Missouri Botanical Garden, St. Louis, in 1989. That account was based on Webster's generic con­ cepts (1987). However, papers by H.-J. Esser (1994,2001) dealing with the tribe Hip­ pomaneae offered new concepts on generic delimitations within this tribe, the largest of the subfamily. Esser's concepts being in closer agreement with wood anatomical features than Webster's classification (1994), the tribe Hippomaneae is treated here following the work ofEsser. In Webster's treatment (1994) the tribe Hippomaneae com­ prises 19 genera in 3 subtribes, whereas Esser (1994) recognized 36 genera and no sub­ tribes. However, in the recent elaborate overview of the subfamily by Radcliffe-Smith (2001), wherein Esser treated the tribe Hippomaneae, the tribe is split into two subtribes: Carumbiinae and Hippomaninae. MATERIAL AND METHODS The 34 genera studied are listed in Table 1. Of a number of genera no wood was available. For the greater part this concerns shrubby and monotypic genera. For two of these, data were taken from literature. Neither wood nor data were available of the following genera: Adenopeltis, Anomo­ stachys, Bonania, Conosapium, Dendrocousinsia, Ditrysinia, Endadenium, Hamilcoa, Microstachys, Monadenia, Senefeldera, and Spegazziniophytum. Data of the wood samples studied are recorded under the generic descriptions. Genera are treated alphabetically according to tribes and subtribes. Most samples are backed by herbarium vouchers and deposited in the collection of the Wood Anatomy section of the Nationaal Herbarium Nederland, Utrecht University branch. Others were pro­ vided by other institutes, cited in accordance with Stern's Index Xylariorum 3 (1988). Microscopic slides and macerations were prepared in the usual way. All slides are deposited in Utrecht (Uw). Density data were only occasionally available, depending on the size of the wood specimen, or records in the literature. Downloaded from Brill.com10/09/2021 12:24:23AM via free access Mennega - Wood anatomy of the Euphorbioideae (Euphorbiaceae) 3 Table I. Genera of the subfamily Euphorbioideae of wh ich wood was examined. Classification according to Radc1iffe-Smith's Genera Euphorbiacearum (200 I). Tribe 1. Stomatocalyceae (Müll. Arg.) G.L. Webster Subtribe Stomatocalycinae Pimelodendron Hassk. Plagiostyles Pierre Subtribe Hamilcoinae Nealchornea Huber Tribe 2. Hippomaneae A. Juss.ex Bartl. Subtribe Carumbiinae Homalanthus A.Juss. Subtribe Hippomaninae Actinostemon Mart. ex Klotzsch Balakata Esser Colliguaja Molina Dendrothrix Esser Excoecaria L. Falconeria Royle Grimmeodendron Urb. Gymnanthes Sw. Hippomane L. MabeaAubl. Maprounea Aubl. Neoshirakia Esser Pleradenophora Esser Pseudosenefeldera Esser Rhodothyrsus Esser Sapium Jacq. Sclerocroton Hochst. Sebastiania Spreng. Senefelderopsis Steyerrn. Shirakiopsis Esser Spirostachys Sonder Stillingia Garden ex L. Triadica Lour. Tribe 3. Pachystromateae (Pax & K.Hoffm.) Pax Pachystroma (Müll. Arg.) Pax Tribe 4. Hureae Dumort. Hura L. Tribe 5. Euphorbieae Blume Subtribe Anthosteminae Anthostema A. Juss. Dichostemma Pierre Subtribe Neoguillauminiinae Neoguillauminia Croizat Subtribe Euphorbiinae Chamaesyce Gray Elaeophorbia Stapf Euphorbia L. Pedilanthus Neck. ex Poit. Synadenium Boiss. Downloaded from Brill.com10/09/2021 12:24:23AM via free access 4 IAWA Journal, Vol. 26 (1), 2005 SURVEY OF THE WOOD CHARACTERS OF THE SUBFAMILY - Table 2 Physical properties Most woods are of medium density, yellowish brown or cream-coloured, and mostly without distinction between heart- and sapwood. Hard, dark brown, often yellowish­ ly streaked heartwood is present in Gymnanthes lucida, Hippomane maneineIla, Spiro­ stachys africana and S. venenifera. Low-density wood occurs in Hura and Euphorbia. Anatomical characters Growth rings - Nearly always present, but inconspicuous. Indicated by a few rows of radially compressed, sometimes thicker-walled latewood fibres. Vessels - Generally diffuse, but in Actinostemon, Gymnanthes p.p., Pseudosene­ jeldera and Rhodothyrsus a striking radial zonation of alternating strips with or devoid of vessels occurs (Fig. 8, 37). Usually the majority in radial multiples of 2 to 4, often dumbbell-shaped (Fig. 13) or in twin rows, also often in clusters. Frequency from few per sq. mm in Elaeophorbia, Hura, Sapium to numerous in species of Chamaesyce, Pseudosenejeldera, Spirostachys. For the greater part between 10-25 per sq. mm. Tan­ gential diameter very small to large, most frequently 100-200 f-lm; often rather vari­ able within a genus. Perforations almost exclusively simple, only in Maprounea part of the perforations scalariform. In juvenile wood of Euphorbia grandicornis Uhlarz and Kunschert (1976) noticed a rare scalariform perforation plate. Ray-vessel perforations (perforated ray cells) were observed in several genera (Fig. 35; see also Giraud 1983). Intervessel pitting generally alternate, the bordered pits 4-16 f-lm in tangential diameter, largest in Hura and Sapium. In Euphorbia from alternate to opposite and scalariform in the cactoid species. Vessel-ray pitting usually large, half-bordered, the shapes regular or variable. The pits in Euphorbia p.p. and in Hippomane are large, elongate to scalariform; pits of two types occur often in one cell. Thin-walled tyloses in species of Anthostema, Excoecaria, Hippomane, Hura, Mabea, Plagiostyles, Pseudosenejeldera, and Sapium. Dark resin in Spirostachys. Vascular tracheids occasionally present in all genera