Apparently this vegetable is used more often in parts of Europe than other places. It appears to be a cross between parsnips and parsley. The tops have the appearance of parsley and the bottom like parsnip. Both parts are eaten, and has a flavour that enhances soups amongst other uses.
I grew it one year for the benefit of a Hungarian lady from the old country. The seeds must be fresh from the previous years crop, similar to parsnip seed or germination is iffy.
"Parsley Root (Petroselinum crispum tuberosum aka Petroselinum hortense).Hamburg parsley, sometimes called parsleyroot, looks like regular flat-leaf parsley when it is growing in the garden. While the tops can be used just like parsley, the swollen root is also eaten both raw and cooked."
Anybody grow this on a regular basis?