O. istriensis was first described from the Istrian peninsula of Croatia by Hertel, Paulus and Weyland in 2016 and so far as is currently known, restricted in range to the municipalities of Rovinj and Bale.

This species is a difficult one to identify, with the two most significant differentiators being the size of the flower and its flowering period. Other morphological characteristics such as colouration, shape and lip pattern are unreliable as O. istriensis is hugely variable. As evidenced by the photographs, it appears in many forms, often closely resembling its compatriot species.

The Istrian Orchid as it is commly referred to, is typically a robust plant with up to twelve, relatively large flowers that appear in mid April, at the same time as the very similar but smaller flowered O. untchjii, with which it frequently associates. O. medea and O. tetraloniae are similarly smaller flowered but will be at their best only as O. istriensis is fading. Sepal colouration is highly variable, ranging from dark pink (rare) to pure white, with green being the most usual. The stigmatic cavity is conspicuously large, being widest at the base and usually merging into a sizable and concolorous basal field. Basal swellings are always present and these may be significantly proportioned, close set and usually forward pointing unlike those of O. untchjii which are generally splayed outwards.

O. istriensis can appear in conventional fuciflorid form (4), trapezoid (9) or very rarely, scolopaxoid, as in the photo opposite. Their is always a submarginal band of hair and unlike O. untchjii, this is both brighter and longer in the basal half of the lip. Although the number of known sites for this species is relatively small, it can occur in significant numbers. The photos date from the 7th of May 2016.