And another thank you to Taisha for writing today's entry:
These Eucalyptus racemosa (syn. Eucalyptus signata) images (image 1 | image 2) were uploaded to the Botany Photo of the Day Flickr Pool by regular BPotD contributor dustaway@Flickr. Thank you dustaway!
Eucalyptus is a large genus, and those who work with the genus frequently may divide it into subgeneric groupings (with each grouping having some common characteristics). For example, Eucalyptus racemosa, or the narrow-leaved scribbly gum, belongs to the Series Psathyroxyla. This grouping has varied in size from as few as four species to as many as ten (see: Atlas of Leaf Venation and Oil Gland Patterns in the Eucalypts, but whatever the size and taxonomic treatment, it has always included the informal group of trees known as the scribbly gums. Members of this informal group are distinguished by the markings on their bark, as well as possessing raised fruit discs, mostly hemispherical fruit, and small seeds.
Scribbly gums are trees or mallees (a mallee refers to species with a mallee habit) that are restricted to eastern Australia: the woodlands on the coast of southern Queensland and New South Wales, as well as tablelands and southwestern slopes in NSW. Species can have a patchy distribution within their respective ranges, but when found, are often locally abundant. They tend to grow in infertile, sandy or stony soil on ridge tops or rises. Occasionally, and only in coastal New South Wales, they can also be found on sandy and sometimes swampy flats (see: Pfeil, B., Henwood, M. (2004). Multivariate analysis of morphological variation in Eucalyptus series Psathyroxyla Blakely (Myrtaceae): taxonomic implications. Telopea. 10(3):711-724).
The characteristic markings of scribbly gums on their otherwise smooth bark are due to the scribbly gum moth (Ogmograptis scribula). The larvae of this moth species bore a meandering tunnel through the bark of affected trees. At first, the loops are long and irregular. Later, a zigzagging pattern is produced, then doubled up after a narrow turning loop. In response to the larval boring, the bark-producing process by the cork cambium is altered somewhat, and scar tissue is produced. The thin-walled scar tissue cells patch up the larval tunnels. However, the cells of the scar tissue are highly nutritious and ideal food for the caterpillars. After the larva molts into its final stage with legs, it reverses direction, eating the scar tissue cells as it goes. It then begins to mature rapidly, until it leaves the tree to spin a cocoon and pupate at the base of the tree. Shortly after the caterpillar leaves, the bark of the tree cracks off, exposing the scribbles underneath.