Darryl Green was visiting the Chickerell Down Woodland Trust site, near Weymouth, in the Spring of 2013 when he saw Orange Tip butterflies laying on on a plant he didn’t immediately recognise.
Subsequent research suggested it was dittander (Lepidium latifolium), which is a rare plant in Dorset.
Returning to the site a few weeks later, Darryl was able to find 2 large caterpillars (full size, nearly ready to pupate), plus 3 smaller (less than 20mm), so the plant was obviously well suited to these butterflies.
Dittander is a plant that it is native on some coasts in east and south England, as well as being naturalised at some sites inland like the Grand Union Canal in London.
In past days it was a standard herbal treatment for leprous sores, as well as being used as a food flavouring before horse radish – Darryl can confirm the latter (not the former!) because he tried it and says it has a hot, peppery taste.
Robin Walls, Dorset Plant Recording Officer, comments that that though the plant is rare in Dorset, Chickerell Downs could be a possible site.
It will have to wait until next year to check the identification: there are other plants of the pepperwort family present in Dorset with which it could be confused, especially if early grazing had damaged the growth of the plant.
Bill Shreeves, Records Officer for the Dorset Branch of Butterfly Conservation said:
I have had a quick search through ancient & modern Butterfly literature and can find no mention of dittander as a food-plant for the Orange Tip, though it belongs to the crucifer group as do the butterfly’s other food plants. It is possible that the counties on the east and south coast, where the plant is thought to be native & grows on shingle, might have recorded it as an Orange Tip food-plant.
The certain identification of the plant will have to wait until it comes up again in 2014, but if you have any knowledge of it as an Orange Tip food plant, please let us know.
Well done to Darryl for his sharp observation, and thanks to him for letting us know about it.