Timber Identification of Autranella, Baillonella and Tieghemella in The
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Deklerck et al. Plant Methods (2021) 17:64 https://doi.org/10.1186/s13007-021-00766-x Plant Methods RESEARCH Open Access Timber identifcation of Autranella, Baillonella and Tieghemella in the taxonomically challenging Sapotaceae family V. Deklerck1,2*† , E. Price3,4†, S. Vanden Abeele5, K. Lievens1, E. Espinoza4 and H. Beeckman1 Abstract Background: To enforce timber import laws and perform timber species identifcation, the identity of the botanical species must be well-defned. Since the Sapotaceae family is known as a taxonomically challenging family, we focus in this study on the four most valuable Sapotaceae timber species from tropical Africa: Autranella congolensis (De Wild.) A.Chev., Baillonella toxisperma Pierre, Tieghemella africana Pierre and Tieghemella heckelii (A.Chev.) Pierre ex Dubard. The wood anatomical characteristic fber lumen fraction and Direct Analysis in Real Time—Time of Flight Mass Spec- trometry (DART-TOFMS) were used to diferentiate the four species and to make inferences on species delineation and taxonomic identity. Results: We observed diferences in the fber lumen fraction measurements and discerned two groups: (1) A. con- golensis and B. toxisperma, and (2) T. africana and T. heckelii. In addition, all Mann–Whitney U comparisons and difer- ences in distributions (Kolmogorov–Smirnov) for the fber lumen fraction measurements were signifcant between all species. When permutating the data between species within those two groups, signifcant diferences were still found between the species within those groups. This could indicate that the fber lumen fraction is not diagnostic to discern the species. DART-TOFMS analysis showed that A. congolensis and B. toxisperma have distinct chemotypes, while T. heckelii and T. africana have remarkably similar chemotypes. Conclusions: Based on our observations of similar chemotype and weakly diferentiated fber lumen ratio, we sup- port an alternative taxonomic hypothesis that considers Tieghemella monotypic, because of the strong resemblance between T. heckelii and T. africana. Larger sample sizes and further research is required to develop methodology for the identifcation of these species. A taxonomic study utilizing molecular genetics would be benefcial to assess the status of the genus and the species limits. This could have implications towards their potential inclusion on CITES appendices if there is ever need for them to be listed. If Tieghemella africana and T. heckelii remain two distinct spe- cies, they should both be listed. Screening agents should be aware that the morphological and chemical diferences between T. africana and T. heckelii are minimal. Keywords: Sapotaceae, DART-TOFMS, Wood anatomy, Timber identifcation, Taxonomic identity Introduction Illegal logging and timber forensics It is estimated that 30 to 90% of timber from the tropics *Correspondence: [email protected] is illegally sourced [1–6]. In addition to ecological dam- †V. Deklerck and E. Price contributed equally to this work as frst authors 1 Service of Wood Biology, Royal Museum for Central Africa (RMCA), age, there are substantial economic and social problems Leuvensesteensweg 13, 3080 Tervuren, Belgium associated with timber poaching [4]. Tese issues have Full list of author information is available at the end of the article sparked an increased demand for timber identifcation © The Author(s) 2021. 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The Creative Commons Public Domain Dedication waiver (http:// creat iveco mmons. org/ publi cdoma in/ zero/1. 0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Deklerck et al. Plant Methods (2021) 17:64 Page 2 of 10 and timber traceability techniques, with current front- Tieghemella africana is well-known to the international runners being wood anatomy, both traditional and with timber trade as Douka [24]. Tis trade name can occa- machine vision [7–9], Direct Analysis in Real Time Time- sionally cover timber from B. toxisperma and is often of-Flight Mass Spectrometry (DART-TOFMS) [10–12], considered as the same trade category as wood from T. genetic analysis [13] and stable isotope ratio analysis [6, heckelii. However, T. heckelii is traded under the generic 14]. trade name (or pilot name) Makoré, which can include Wood anatomy, DART-TOFMS and genetic analy- timber from T. africana and B. toxisperma. Tieghemella sis are currently the most employed methods to deter- africana is typically found in the evergreen rainforests mine the species identity of timber. However, timber from Cameroon to Cabinda (Angola) in the west, and import laws and adjoining timber species identifcation eastward to the Republic of the Congo and Democratic can only be followed if the identity of the botanical spe- Republic of the Congo (DRC) [25]. Te highest spe- cies is well defned. Until three decades ago, taxonomists cies densities are reported in Equatorial Guinea, west- mainly used morphological traits to describe and delin- ern Gabon and in the Republic of the Congo, north of eate species. However, species can show high levels of Kouilou. In other regions it can be mixed with T. heckelii intraspecifc morphological variation, which complicates and B. toxisperma. Heartwood of T. africana is very simi- accurate species delineation and occasionally results in lar to T. heckelii but tends to be more intensely stained the erroneous splitting of species. Conversely, diferentia- with a more distinct vein pattern (for an image of the tion and speciation are not always accompanied by mor- heartwood of all species, please see Additional fle 1: Fig- phological change, as demonstrated by the abundance ure S1). In provenances from the Republic of the Congo, of cryptic species [15–17], where two or more distinct the wood has been noted to darken to a red violet colour. genetic lineages are classifed under the same taxonomic In addition, T. africana tends to be slightly harder and unit because they are seemingly indistinguishable from heavier than T. heckelii. Te main distribution area for T. a morphological point of view [15]. For this reason, it is heckelii covers eastern Liberia, Côte d’Ivoire and Ghana, important to include molecular data when new species but the species also occurs in lower densities in Nigeria are described and named. Even when DNA-based meth- [26]. As such, the range of T. heckelii overlaps with other ods are incorporated, genetic divergence can remain morphologically similar Sapotaceae species, creating a undetected resulting in wrongly delineated species. Rea- challenge for feld identifcation. Baillonella toxisperma sons for this can include homoplasy (a shared character and A. congolensis occur in low densities in the rainfor- that did not arise from a common ancestor) and evolu- est of southern Nigeria, Cameroon, Equatorial Guinea, tionary processes such as hybridization (production of Gabon, Cabinda (Angola), Republic of the Congo and the viable ofspring by parents from diferent varieties or spe- Democratic Republic of the Congo (DRC) [27, 28]. Bail- cies), chloroplast capture (introgression of a chloroplast lonella toxisperma (Moabi), can look very similar to T. genome from one species into another), reticulate evolu- heckelii, but the distinction is clearer than for T. africana tion (or network evolution, where a group of organisms from Ghana or the Ivory Coast. Baillonella toxisperma originates through the partial merging of ancestor line- is also found mixed with shipments of T. africana and T. ages) or incomplete lineage sorting (common ancestry of heckelii. Autranella congolensis is reported to be falsely gene copies at a single locus extends deeper than previ- sold as B. toxisperma, but Autranella congolensis wood is ous speciation events) [16, 18–20]. harder and darker with a violet colour. Standing trees of B. toxisperma and A. congolensis are quite similar to each Sapotaceae other, with one primary diference being B. toxisperma Te Sapotaceae family is known for its highly homopla- exhibits a distinctively fatter crown [24]. sious morphological characters and the lack of unam- biguous synapomorphies for subfamilies and tribes [21], Taxonomic history leading to the dynamic nature of the Sapotaceae taxon- Although the four Sapotaceae species in this study are omy and the many taxon synonyms [22]. Here, we will currently assigned to three distinct genera, all four spe- focus on the four most important Sapotaceae timber cies were previously included in the genus Mimusops species from tropical Africa: Autranella congolensis (De [22]. Autranella congolensis seems to be related to the Wild.) A.Chev., Baillonella toxisperma Pierre, Tieghe- latter, but it difers in having stipules, a longer corolla