Structural diversity of the wood of temperate species of Acacia s.s. (Leguminosae: Mimosoideae)

Abstract

Acacia s.s. comprises approximately 1020 species (i.e. just under one-third of all mimosoid legumes) and is almost entirely restricted to, although widespread, on the Australian continent. We investigated variation in the wood anatomy of 12 species from temperate New South Wales in a study concentrating on four recognised taxonomic sections (Botrycephalae, Juliflorae, Phyllodineae and Plurinerves), to elucidate which characteristics are consistent within the sections, having removed climatic effect as much as possible. The sections had great utility in species identification, whereas none of the wood characters reflected the hypothesised phylogeny of the genus. The main consistent difference among species was in ray width (uniseriate versus 1–3 cells wide). All species had distinct growth rings. The vessels had alternate vestured pitting and simple perforation plates. Fibres were generally thick-walled, and many fibres had a gelatinous inner wall (tension wood fibres) and were inconsistently distributed. Axial parenchyma was mainly paratracheal, ranging from vasicentric to confluent and varied greatly in abundance. Prismatic crystals were usually present in chambered fibres and axial parenchyma strands, and also varied in abundance. The variation in these qualitative characters obscures taxonomic differences, but may allow inferences to be made about environmental adaptation.

Climate trends in the wood anatomy of Acacia sensu stricto (Leguminosae: Mimosoideae)

“…The likelihood of deformation of vessel walls under cavitation has been hypothesized to be mitigated by the greater strength of the thick-walled fibres (Jacobsen et al, 2005). That this is a role for thick-walled fibres in Acacia s.s. can be questioned given the abundance of paratracheal parenchyma, and the lack of fibres in direct contact with vessels in species from arid and semi-arid regions, as also noted by Whinder et al (2013) for temperate species of Acacia. All the species studied have paratracheal parenchyma, which provides further support for questioning of this phenomenon.…”

“…The species of Acacia s.s. (hereafter referred to as Acacia) are distributed across the continent of Australia and form the dominant element of many vegetation types. Growing across a broad range of climates and edaphic environments, Acacia is morphologically heterogeneous, with a wide diversity of growth form, vegetative and floral morphology, and anatomy (Boughton, 1986(Boughton, , 1990Whinder et al, 2013). Climate and particularly precipitation have been identified as the major factors determining the broad geographic patterns of distribution and abundance of the species of Acacia (Hnatiuk and Maslin, 1988;Maslin and Pedley, 1988).…”

“…More comprehensive studies by Baas et al (2004) found support for ecological trends in vessel characters as generalized by Ford (1984). Whinder et al (2013) pursued this theme with 12 temperate Acacia species from New South Wales, and included vessel, fibre, axial parenchyma, ray and crystal characteristics in their study. The other main ecological wood anatomy study of Australian Acacia melanoxylon R.Br., by Wilkins and Papassotiriou (1989), compared a wider range of characteristics with latitude and the associated general climate, with limited samples allowing for only broad conclusions to be drawn.…”

Fibre dimorphism: cell type diversification as an evolutionary strategy in angiosperm woods

“…They are interpretable as an herbivore‐deterrent mechanism, but if that were the selective factor, one might expect lignified walls instead of gelatinous walls. The possibility that gelatinous fibres may store water and play roles in accordance with that has been raised (Sonsin et al ., ; Whinder et al ., ).…”