This tuberous root of wild cucumber, Marah gilensis, was uncovered accidentally while digging a hole for another plant at Boyce Thompson Arboretum. Dense and pithy, it’s a powerhouse of stored starch that resides just below the soil surface. Quick-growing vines emerge from it each spring and clamber drunkenly through nearby jojobas and hackberries. It’s a botanical oddity that is rarely seen, but never under appreciated. At 50 pounds, this specimen is a granddaddy: a certified, subterranean lunker.