Stems, Roots & Buttresses
Diversity in Stems, Roots & Buttresses
Adaptations concerning above-ground breathing roots are essential for gas exchange in saturated, non-porous soils depleted in oxygen. Another attribute helping survival in water-saturated environments are structures to support the above-ground mass of the tree. Where roots are unable to penetrate more than a metre or so because of the anaerobic conditions, then lateral support structures provide an important contribution.
Roots above-ground come in various types including: pneumatophores as pencil-like (like Avicennia spp.), stiff conical (like Xylocarpus moluccensis), flexible conical (like Sonneratia alba), elongate conical (like Sonneratia caseolaris, Sonneratia lanceolata); knee roots as thick and knobbly (like Bruguiera spp.), thin and wiry (like Lumnitzera littorea); stilt roots (like Rhizophora spp.); and buttresses as sinuous planks (like Xylocarpus granatum, Heritiera littoralis, Ceriops spp.), and erect ‘fins’ (like Bruguiera X rhynchopetala, Xylocarpus moluccensis). Roots are used by various fauna, but the most notable are the teredo shipworms, plus termites and crabs.
Left - dense tangle of stilt roots of Rhizophora species, near Cairns, Queensland.
- Unusually exposed cable roots of Avicennia marina.
- Distinct pneumatophores of Sonneratia caseolaris.
Beauty is in the bark
Bark characteristics vary in: texture from smooth (like Avicennia marina var. eucalyptifolia), to flaky (like Xylocarpus moluccensis), to fissured (like Lumnitzera spp.), to pustular (like Excoecaria agallocha), to friable & crumbly (like Bruguiera gymnorhiza), to crocodile skin (like Rhizophora apiculata); and colour from red (like seaside Rhizophora stylosa, Avicennia integra), grey (like Avicennia marina var. australasica), white (like Camptostemon schultzii), green (like Avicennia marina var. eucalyptifolia), brown (like Bruguiera pariflora) and black (like Lumnitzera spp.). Bark is used by a range of fauna including insects such as molluscs, termites, ants, boring beetle larvae, crickets and roaches, plus small reptiles like geckos and skinks.
Stem and bark of a young sapling of Rhizophora stylosa, with Littorinids
- Avicennia marina and ant.
- Bruguiera gymnorhiza
- Osbornia octodonta
- Lumnitzera racemosa
- Excoecaria agallocha