Many people have chatted to me about the differences between the 3 UK populations of Monkey orchid and to be honest I am not an expert so this is really just my opinion, based on what I have heard and seen.
Geographically, the 3 colonies are quite far apart, with Hartslock being by far the most northerly and westerly site. The other 2 colonies are in Kent, at Park Gate Down and a secret site on private land.
My understanding is that the private site is the oldest surviving Kent colony, with records dating back to 1955*. I visited the site in 1997, with a Kent Trust’s reseve manager, and it proved to be a fairly small piece of downland surrounded by trees. The Monkey orchids grew in the woodland and on the grassland but at the time it was quite a dry year and rabbits had been taking their toll so numbers were low.
Hector Wilks, of the Kent Trust for Nature Conservation, did sterling work there in the late 1950s to boost numbers using hand pollination and in 1958 he sowed seeds on Park Gate Down – a nice piece of downland owned by the Kent Trust and already home to some rare UK orchids. The Monkey orchids thrived there and this is now the main Kent site and the easiest place to see the orchids.
Hartslock has documented records dating back a lot further than the Kent sites. I have seen a herbarium sheet marked “Hartslock Wood, Goring” and dated 1831; while I think Druce cites documentary records for the Goring Gap and Wallingford area dating back to the 1620s. I have seen further herbarium specimens from: Caversham (labelled “Cawsham Hill”) dated 1778; Mapledurham dated 1850; and Whitchurch dated 1878. So it seems clear that they used to grow all along the south Chiltern escarpment.
It’s impossible to go much further back in time because non-medicinal plants were not given stable names or really studied before the 1600s, but it seems highly likely that they have existed in this part of the country since the last ice age and that the south Chilterns is probably the oldest location for the species.
In terms of plant stature, the Park Gate plants are usually much taller and more robust than the other 2 colonies. It has been suggested that this indicates a continental origin but really I think it just reflects the fact that the soil at Park Gate is quite nutrient rich and generally wetter than the other sites. Park Gate’s plants came from seed gathered at the private site and the plants there look very similar to those at Hartslock, growing on similar nutrient-poor, dry soils.
* Lang, David (1989). A Guide to the Wild Orchids of Great Britain and Ireland.