I remember years ago ordering seed of a special heirloom heritage radish “rat’s tail” (Raphanus sativus var caudatus) through the Heritage Seed Library in the UK. I remember that it was the gardener at naturalist Gilbert White’s House and Gardens at Selbourne in Hampshire that offered the seed and I remember that we ended up trading seed as they were looking for plants that Gilbert White mentioned; see  https://gilbertwhiteshouse.org.uk/gilberts-gardens 
The resultant plants had long green pods. However, I lost them eventually.  Subsequently I’ve tried seed of rat’s tails several times and the pods have never been as long as those original plants. 
Radishes are difficult to grow here in spring as our long days result in them quickly bolting (still looking for a good day neutral variety). I remember reading that when wild radish Raphanus sativus was originally domesticated in China that it was for the young seed pods rather than the swollen tap roots. 
I therefore decided this winter to source various rat’s tail radishes from commercial sources and also obtained seed of 4 (of 8 available) accessions from the German genebank IPK Gatersleben. There was no available descriptons, so this was a random selection. They were sown in May in the World Garden (Verdenshagen) at the Væres Venner Community Garden (NB! I do grow a few annuals on the world garden if they have an interesting geographical story associated).
Yesterday I harvested a few of each and was blown away by the diversity with long red, thin green and two more stumpy varieties like I had been getting in recent years when ordering rat’s tails. Below is what Cornucopia II says on this interesting vegetable. 
Assuming like me that you will want to grow your radishes to seed for the following year, the land is occupied all season in any case, so rat’s tails produce more than root radishes. The flowers are also also rather pretty bicoloured pink and white and area also attractive to pollinators! I think I will save seed and deveop a mixed grex of these and more varieties from the gene bank next year!
And this gave the opportunity for a unique rat’s tail salad for lunch with radish flowering tops too, also delicious (see the pictures at the bottom) :)

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