A sphaeroblast is a woody extrusion from the trunk or branch of a tree, usually taking the form of a rounded spherical shape, as if the tree had a boil or mole.[1]
Sphaeroblasts originate from a bud initial or a cluster of buds (especially adventitious buds) on the trunk or branch that have abnormally generated a rounded layer of cambium and then subsequently secondary thickened to produce wood (xylem), rather than growing shoots or foliage.[2] It is possible that sphaeroblasts are formed in the presence of microbes, as is the case with a witch's broom formed in a tree, but there has been little scientific research on what causes sphaeroblasts to form and it may be the case that there are a number of different causes of this anomalous growth form, pathogenic or physiological.[citation needed]
Sphaeroblasts are quite common on species of beech (Fagus), holly (Ilex), horse chestnut (Aesculus) and southern beeches (Lophozonia), and also occasionally appear on quite a wide range of other tree species, including conifers. They can be of interest to wood carvers, to create unique wooden ornaments. Their removal from the tree typically causes only a small wound to the trunk or branch, as they are often only superficially attached [3]
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Sphaeroblasts formed at the base of a southern beech (Lophozonia alpina) -
An image of a sphaeroblast formed on a mature beech tree (Fagus sylvatica)
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There is no known case where the presence of sphaeroblasts has resulted in dieback or structural failure in a living tree[citation needed]. Sphaeroblasts represent only a very minor distortion of tree growth and are not considered to be a sign of ill-health in a tree.
References
edit- ^ Strouts R G and Winter T G (1994) Diagnosis of ill-health in trees, TSO: London
- ^ Watson B (2013) Trees: Their use, management, cultivation & biology, Crowood Press Ltd., England
- ^ Ruhland W ed. (1965) Encyclopedia of Plant Physiology vol. XV: Differentiation and Development, Springer-Verlag: Berlin