Sunflowers (2008)

''There is a time in every author's relationship with a topic when he crosses the line into obsession,'' says the affable Joe Pappalardo, who seems to find sunflowers everywhere: He claims Hitler invaded Russia because he wanted the country's sunflower oil and notes that another form of the weed, the Jerusalem artichoke, was rejected as a food source in 17th-century Europe (which is unfortunate, since its use could have averted the Irish potato famine). Though some of Pappalardo's interview subjects in Sunflowers exude a standard scholarly dryness, Pappalardo himself does not in this lively, compulsively readable account. B+