Unveiling the wood anatomy of the overlooked agarwood Aetoxylon sympetalum (Steenis & Domke) Airy Shaw (Thymelaeaceae Juss.).

Agarwood is one of the most valuable non-timber forest products due to its gratifying aroma. This has led to overexploitation of agarwood produced by species from Thymelaeaceae such as Aquilaria spp., Gyrinops spp., Gonystylus spp. and a mostly unnoticed species, Aetoxylon sympetalum. Although a candidate, A. sympetalum has not been included in CITES, in contrast with other agarwoods. This could be due to the difficulty in identifying this species because of a lack of information regarding its wood anatomy. The aim of this study is to elucidate the wood anatomy of A. sympetalum and thereby determine the features that distinguish this species from other agarwood species. Three wood samples of A. sympetalum were examined and sectioned. The resulting slides were then compared with the reference sample in the slide collection of the Jodrell Laboratory in the Royal Botanic Gardens, Kew. More samples were prepared for observation under scanning electron microscopy. The anatomical features were described according to the standard IAWA terminology. A. sympetalum is a diffuse-porous wood, with alternate and minute intervessel pits, vestured pits, very thick-walled fibres; mostly uniseriate rays and prismatic crystals within ray cells. The absence of diffusely arranged islands of phloem differentiates A. sympetalum from Aquilaria spp. and Gyrinops spp. The only noticeable difference with Gonystylus spp. is the thickness of the fibre walls which results in very high-density wood. The wood anatomy described agrees with Mandang & Wiyono (2002) but varies greatly from Tian et al. (2021) which is arguably a misidentification. This study is a reference point for identifying A. sympetalum which is paramount to its potential conservation and thus encourages its inclusion within CITES.