Sunday, April 26, 2015
Botany picture #200: Xeranthemum inapertum
Xeranthemum inapertum (Asteraceae), France, 2014. Here in Australia we have lots of Asteraceae in the paper daisy tribe Gnaphalieae that have lost the otherwise fairly daisy-typical petal-like ray florets but then went through the evolutionary equivalent of regretting that loss, so they evolved papery colourful radiating bracts to serve as pseudo-petals. In the Mediterranean area we can find two other groups of Asteraceae that have done precisely the same thing, only they belong to the thistle tribe Cardueae instead.
The above genus Xeranthemum consequently looks very unlike a thistle (and it doesn't even have spines). In fact the well-known golden everlasting Xerochrysum bracteatum, a typical Australian Gnaphalieae, was originally described as a Xeranthemum, the systematic equivalent of describing an Acacia as part of the clover genus Trifolium. Of course that was in 1803, and the mistake was corrected only two years later.