O. guimaraesii was first described from Estremadura, Portugal as a subspecies by Tyteca in 2000. It was subsequently promoted to full species status by Kreutz

The range of this orchid is not dissimilar to that of O. tenthredenifera, though it is absent from the Balearic islands, The two species share the same pollinator (Eucera nigrilabris) but O. guimaraesii differs primarily in its significantly smaller size (both plant and flower) and its earlier flowering period. It has been recorded as being in flower from the end of December but more usually appears in February and is often to be found flowering concurrently with O. tenthredenifera through March.

O. guimaraesii exhibits a lip which is usually strongly or moderately recurved with a small appendage and only a sparse tuft of hair above it. These are however features not uncommon in O. tenthredenifera and therefore size and phenology remain the most important differentiators. It should be mentioned that some authorities do not consider O. guimaraesii a taxon that warrants full species status.

The pictures are from Alicante, dating from mid March.