Systematic and Ecological Wood Anatomy of the Erythroxylaceae
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IAWA Bulletin n.s., Vol. 6 (4), 1985 365 SYSTEMATIC AND ECOLOGICAL WOOD ANATOMY OF THE ERYTHROXYLACEAE by Phillip M. Rury Bailey-Wetmore Laboratory of Plant Anatomy & Morphology, Harvard University Herbaria, Cambridge, MA 02138, U.S.A. Summary Introduction The wood anatomy of 67 species of Ery The Erythroxylaceae constitute a pantropi throxylum, Nectaropetalum and Pinacopodium cal, woody dicotyledonous family of 200-250 was analysed from an ecological, systematic species of trees and shrubs, the vast majority be and evolutionary perspective. Wood anatomy longing to the genus Erythroxylum P. Browne. variation within the pantropical genus Ery Erythroxylum exhibits maximum diversity in throxylum is explicable largely in relation to the neotropics, with at least 150 species rang ecological factors and correlative differences in ing from Mexico and the West Indies south plant architecture, leaf size and duration and ward to Bolivia, N. Argentina, Brazil and Uru foliar anatomy. Wood anatomy ranges between guay. Thirty species of Erythroxylum are en primitively mesomorphic and either meso- or demic to Africa and adjacent islands, with at xeromorphically specialised. Wood inclusion least fourteen species in southern Asia and the type and leaf structural features are strongly Malayan archipelago, with three species each in interrelated, thus reflecting both taxonomic Australia and the Pacific proper. The other affinities and ecological profiles of the species. genera are the monotypicAneulophus africanus The most wood anatomically variable infra Benth., endemic to equatorial West Africa, generic taxa within Erythroxylum are the New Nectaropetalum Engl., with some nine species World sections Archerythroxylum and Rhabdo in tropical and southern Africa or Madagascar, phyllum, which include architecturally diverse, and Pinacopodium Exell & Mendonr;a, with deciduous and evergreen species. Due to the two species restricted to tropical Africa. intergrading ranges of wood anatomical varia Species of Erythroxylum occupy a wide tion among consectional and/or sympatric range of habitats, including lowland and mon Erythroxylum species, attempts to identify tane rainforests from sea level to an altitude of wood samples to the species level are ill-advised 2,000 metres. Some species of Erythroxylum in the absence of complementary ecological, and Nectaropetalum occur in savannas, open geographic and leaf structural data. The wood dry forest and other arid sites on a wide range anatomical uniformity of the cultivated cocas of granitic, sandy, serpentine or calcareous and their closest wild relatives of sect. Archery soils. Both paleo tropical and neotropical spe throxylum implies their shared mesophytic an cies of Erythroxylum reveal an interesting de cestry, whereas chemical, genetic and leaf gree of habital diversity, and include prostrate structural differences reflect the long term hu shrubs of xeric habitats, rosette shrubs and man selection, isolation and cultivation of Ery small trees of moist and wet forests, and tall throxylum within ecologically disparate regions canopy trees in everwet rainforests. According of South America. Wood (and leaf) anatomy of to Payens (1958), Malesian species of Erythro the drought sensitive E. coca var. coca is the xylum are confined to the substage of the most primitive and mesomorphic of the culti primary rainforest up to an altitude of 1,600 vated cocas, whereas both drought tolerant metres, avoiding areas subject to a dry season. varieties of E. novogranatense are more wood (and leaf) anatomically specialised. The closest Taxonomic history affinities of the Erythroxylaceae to other fami The genus Erythroxylum was first described lies of the Geraniales-Linales-Malpighiales al by Patrick Brown in his 'Civil and Natural His liance occur among the most wood anatomical tory of Jamaica' (1756). Subsequently, Linnaeus ly primitive, mesomorphic and putatively basal, (1759) included the genus in his ~Systema Na evergreen taxa within each family. turae' using the spelling Erythroxylon, which Key words: Erythroxylaceae, Erythroxylum, has since been used by some authors (e.g., Mar cultivated coca, systematic and ecophyletic tius, 1843; Machado, 1972). Plowman (1976) wood anatomy. pointed out this inconsistency and established Downloaded from Brill.com10/03/2021 08:38:44PM via free access 366 IAWA Bulletin n.s., Vol. 6 (4),1985 Erythroxylum as the correct spelling, based on ties of the Erythroxylaceae with other dicoty its priority of publication. ledonous families. In order to translate this Most early authors, including Reiche (1896) growing database into the standardised, com and Schulz (1907, 1931), limited the family to puter-coded format recommended by the two genera, Erythroxylum and Aneulophus. IAWA Committee (1981), a future paper on However, Stapf and Boodle (1909) concluded wood identification in the family will follow that Nectaropetalum should be included, due the study of additional specimens. to its similarity to Erythroxylum in both stem and leaf anatomy. A similar conclusion was Material and Methods reached by Oltmann (1968) on the basis of pol Woods from 140 specimens of 67 species len morphology. Normand and Cavayo (1951) and three genera were obtained from various advocated the inclusion of the new genus Pina xylaria and the collections of W. C. Evans, T. copodium Exell & Mendonya within the family Plowman and J. Schunke V. Wood of the rare, on the wood anatomical grounds and most monotypic Aneulophus africanus was not avail modern authors (e.g., Melchior, 1964; Hutchin able. Wood specimens and voucher information son, 1967, 1969, 1973) now agree that Aneulo are listed in Rury (1982), but are excluded for phus, Erythroxylum, Nectaropetalum and Pina the sake of brevity. Xylaria abbreviations are copodium form the family Erythroxylaceae. those recommended by Stern (1978) and her A long-standing taxonomic problem has been barium citations follow Holmgren and Keuken the resolution of infrageneric relationships of (1974). Ery throxylum. Schulz (1907, 1931) divided Specific gravity was estimated by dividing the genus into 19 sections, primarily on the the dry weight (g) of each sectioning block by basis of stipular and floral morphology. Pay ens the volume (ml) of water it displaced in a 50 ml (1958), however, noted that since Schulz'mono graduated cylinder. At the suggestion of Dr. graph, 'many species have become connected Regis B. Miller (pers. comm.), a moisture con by intergrades and consequently must be tent of 6% was assumed for all dried wood united.' Similar conclusions were reached by samples, and these specific gravity values were Plowman (pers. comm.) who noted that Schulz' then converted to basic specific gravity using sections 'are largely artificial and will have to the graphs provided by Miller (1981). Wood be submerged.' In addition extensive field stud macerations were made with hot (50°C) Jef ies of Erythroxylum throughout its neotropical frey's solution and thin sections were cut on a range have revealed a series of polymorphic sledge microtome. A few of the air-dried wood species complexes (Plowman, pers. comm.). The samples also were prepared for scanning elec interrelationships of these groups and their con tron microscopy using conventional techniques. stituent species are further obscured by prob Wood anatomical variation was statistically lems of synonymy, broad distributional ranges analysed with an analysis of variance (ANDY A) and related clinal morphological variation. 'package program' in a Tektronix 4051 com As noted by Tomlinson (1977), the resolu puter. Tracheary element dimensions are based tion of such complex problems in plant system on 50 measurements per wood specimen and atics requires a collaborative, integrated ap pore densities (vessel frequencies) were calcula proach. Fortunately, Plowman (1979, 1982, ted from ten counts per specimen. Solitary 1984a, b) has clarified the botanical identities pores and radial or tangential pairs were count of coca leaves grown commercially in South ed as single units, whereas radial multiples of America. as the sole natural source of the me three or more pores were scored as three or dicinal alkaloid cocaine and certain flavours more units, so as to accurately reflect relative used in the manufacture of Coca-Cola®. Plow conductive areas among specimens with com man's continuing taxonomic studies of Ery parable pore diameter. throxylum have provided accurately identified In order to permit general ecological inter wood samples, herbarium vouchers and perti pretations of wood anatomical variation, only nent ecological data for both wild and culti data from positively identified specimens of vated, tropical American species. Accordingly, known ecological origin were used to calculate this study was designed to: 1) provide a com species means. Paleotropical wood specimens prehensive wood anatomical circumscription were assumed to have been accurately identi for the Erythroxylaceae; 2) interpret wood fied and were excluded from calculations of anatomical variation from an ecological and species means only in the event of dubious evolutionary perspective: 3) elucidate the infra identity or incomplete documentation. Spec familial relationships of the Erythroxylaceae, imens were analysed in alphabetical sequence including the probable evolutionary origins of according to the infrageneric classification of cultivated coca and 4) further clarify the affini- Erythroxylum by Schulz