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It’s citrus season in the northern hemisphere, and fruit trees are bursting with oranges and lemons. But CrowdScience listener Jonathan wants to know what happened to the tangerines he ate as a child in the 1960s. He remembers a fruit that was juicy, sweet and full of pips, found each Christmas at the bottom of his stocking. Tangerines today, he thinks, just don't compare.

Crowdscience tries to track down this elusive fruit. Presenter Anand Jagatia traces the tangerine's origins back to Ancient China, and finds that the name ‘tangerine’ comes from a fruit exported from the Moroccan port of Tangier - which bears little resemblance to anything grown today. Botanist David Mabberley explains the complex hybridisation process that goes into breeding modern tangerines, but which unfortunately leaves the trees vulnerable to disease.

We discover that the easy peelers of listener Jonathan’s youth have been largely replaced by more commercially viable plants. And we meet a Californian farmer fighting to keep heritage varieties alive. Could one of those be the subject of Jonathan's nostalgia?