Nhu writes in the accompaniment to the photograph:
“In celebration of Darwin’s 200th birthday and the 150th anniversary of The Origin of Species, I have prepared this panel.”
“This is a weedy species that grows in coastal (and some central) areas of California. According to research by Norman Ellstrand‘s group at UC Riverside, this species is evolving in a quantifiable manner. It is a hybrid between Raphanus sativus, the common radish, and Raphanus raphanistrum.”
“Curiously, the same hybrid occurs elsewhere in similar climates such as that of South Africa, but something special about ecosytems in California allowed it to proliferate. It is now different enough from either of its parents that Ellstrand’s group is considering describing this as a new species. This has occurred within the timespan that the two parents were brought together by humans in California.”
“There are many color variations of this evolving species. It is exactly through this variation that the process of natural selection works. If allowed to go its own way, some of these color morphs may persist, others may perish, all depending on the selective forces present where they occur. Eventually, each of these via time and selection could become a species of its own. California thus would be the center of diversity for a new group of Raphanus species.”
The paper from the Ellstrand group detailing “that California wild radish has now become an evolutionary entity separate from both of its parents” is here: Hegde, SG. et al. 2006. The Evolution of California’s Wild Radish Has Resulted in the Extinction of its Progenitors. Evolution. 60(6): 1187-1197. doi:10.1111/j.0014-3820.2006.tb01197.x. From a read of the abstract, it seems that the wild parent species have become extinct (at least locally) and replaced by these hybridized descendants.