The southern marsh orchid is the largest of the marsh orchids generally ranging from 20-70cm though some can reach 100cm (the tallest will almost certainly be hybrids). There is usually 4-6 stout deeply keeled leaves which generally have no markings. There are numerous individual florets which are generally pale pink in colour but can sometimes be a deep purple. They are usually marked with dots and dashes. The lip is generally rounded and slightly lobed with the middle lobe like a tooth. There are many hybrids; particularly the one with common spotted orchid which will show characteristics of both parent species.