Over to Mike who says:
"Mature seeds (achenes) of the two forms of Prickly Lettuce Lactuca serrriola are wanted, to look at any differences.
"The two forms are f. serriola (image above right) with runcinate-pinnatifid leaves and f. integrifolia (image below left) with entire leaves.
"The former is becoming increasingly more frequent in places.
"Preferably, send me a photo of the plant (or a leaf with the achenes) to show the leaf type and put each gathering of seeds in a small folded piece of paper for each plant.
"Please send to Mike Wilcox at 43 Roundwood Glen, Greengates, Bradford, BD10 0HW and/or email me at: firstname.lastname@example.org."
Mike also mentioned that the Prickly Lettuce plants are fruiting where he is in Bradford, so this is the right time for people to go out looking for those mature achenes.
A reminder that if you aren't quite sure what terms such as achene runcinate, pinnatifid or the double-barrelled tongue-twister 'runcinate-pinnatifid' actually mean, there's a helpful botanical glossary here. Happy Prickly Lettuce hunting!