Today I have been writing a lecture about weeds to present to a Master Gardener audience on Thursday. So I have been reading about Yellow Star Thistle, a weed that is believed to have entered California in the mid 1800s in a contaminated batch of alfalfa seed from Chile. But the plant originally came from the Mediterranean, so I guess it got to Chile first, then here. It thrives in a mediterranean hot dry summer region, and so has galloped across California. We hate it because it has sharp spines behind the flowerheads, because it dominates a landscape, using up water that native wild flowers could have used, and because it is poisonous to horses. Horses that eat quite a bit of it (1 to 2 times their body weight) have brains permanently damaged in a way that prevents them from being able to eat or drink.
So, its a nasty weed that now infests 22% of the state of California, or about 20 million acres. We combat it with goats (they can eat it safely), with several insects imported from Greece that live only on this plant, with carefully timed mowing, and with controlled burns. No happy ending in sight, but a lot of thought and energy is now going to trying to reclaim land lost to yellow star thistle. You can read more about it at http://www.cal-ipc.org. Their website includes the entire text and the photos from the book Invasive Plants of California's Wildlands. Search for it by its common name or by Centaurea solstitialis.
I have continued to peer at plants damaged by the hail. Many are now showing pale lesions on the leaves that are caused by the impact of hailstones. I am also frequently seeing pale streaks rather than spots, and I have never seen this before. Clearly the hail was falling so hard that it streaked across the leaves, rather than just hitting and bouncing. Often a streak ends in a tear. Alstroemeria (Peruvian lily) is another species that lost many leaves to the hail.