Thank you to -Merce-@Flickr for today's photographs (original image 1 and original image 2 via the BPotD Flickr Group Pool). Thank you -Merce-!
Michael Charters from Calflora.net explains that the pronunciation of the generic name for this plant has an emphasis on the first syllable, so it is said “SIL-i-bum”. However, that doesn't prevent certain coworkers of mine from repeating the humorous version of the name when they encounter the plant or images of such (I expect today's “word of the day” at work will be “sillybum”).
Humour aside for the moment, blessed milkthistle is a plant native to the Mediterranean area. Where agriculture has gone, though, it has followed, and it is now found in mild temperate areas around the globe. If you can't take the time to read this report on Silybum marianum from the Global Invasive Species Initiative, I'll share two facts that leapt out at me.
One is that seed production of this plant in infested areas can reach and exceed 500kg/ha (or 446 lbs/acre) – a massive amount, and an indication of why this plant can become a problem.
I'll quote the second fact from the site: “...One reason control methods have been sought after is due to the toxic potential of the thistle. Silybum marianum has caused some of the worst cases of stock poisoning in northwest Tasmania. The poisonous principle is nitrate (Macadam 1966). Cattle and sheep eat the plant material which contains potassium nitrate and break it down by means of ruminal bacteria into the poisonous form (Knott 1971). ‘The nitrite ion...combines with haemoglobin to form methaeglobin ...[which is] incapable of combining with oxygen. If large amounts of methaeglobin are present in the blood stream, affected animals will begin to show respiratory distress for lack of oxygen.’ (Knott 1971) Poisoning threats are increased when the plants are wilting after being cut or partly turned under during plowing and in wet weather (or) when soil moisture is high. In dry conditions they are not considered dangerous (Parsons 1973).” (references to further reading on the bottom of the essay on Silybum marianum).
Photography resource link: When Pretty Isn't Enough, the latest essay from Michael Reichmann of The Luminous Landscape, reminds that photographs are a synthesis of the observer and the observed.