Top tips for the two species, so that the more tricky hybrids can be more easily winnowed out.
HYBRIDS. In areas where both species grow, natural hybrids will occur, though the situation is less hopeless than pessimists might think, as peak flowering time is earlier in Large-leaved by 15-20 days and in many sites the true species are readily identifiable. We still need to work out the prevalence of natural hybrids in Herefordshire. Because of back-crossing (introgression), hybrids are variable. Where species boundaries are drawn is a moot point when there might be 25% of one genome and 75% of another.
Hybridisation also occurs within the trees’ main range in continental Europe from where certain hybrids were selected and propagated clonally, especially in the Netherlands, to provide large numbers of plants for the fashionable avenues and walks of grand houses from the late 1600s onwards. This tradition continued into later centuries outwith grand country houses, presumably because the tree fared well in urban environments and the stock was available. Most of these trees belong to a single clone, correctly referred to botanically as Tilia x europaea L. var. europaea, by horticulturalists often as Tilia europaea Pallida, but, thanks to its abundance now widely and simply known as Common Lime.
There are thus 4 trees to get to grips with: Small-leaved Lime, Large-leaved Lime, wild hybrid Lime and Common Lime. These are their usual contexts:
Small-leaved: Old or replanted woodland, sometimes in hedgerows nearby, or planted in parkland and churchyards
Large-leaved: Similar to small-leaved, but rarer, and associated with limestone or calcrete and cornstone within the Old Red Sandstone. Perhaps more frequent as an avenue tree in Herefordshire. Still planted today
wild hybrid Lime: Old or replanted woodland, either alone or in the company of both or perhaps more commonly one parent. Flag the possibility of wild hybrid Lime in your records if there seems to be a mix of significant characters, eg bunches of rusty hairs in the vein axils AND many single, white hairs sticking out at right angles (patent hairs) from the main surface of the underside. Small-leaved is the commoner tree and you may sometimes encounter odd singletons in amongst fair numbers of that species which show at least some traits of Large-leaved, and which may be relicts of the Large-leaved genome. I have found puzzling trees like this at Badnage Wood near Tillington, and near Vowchurch, Whitfield and Dinmore Hill.
Common Lime: Older suburbs of towns, municipal parks, churchyards and the grounds of manor houses and stately homes (which often border on woodland!).