Euphorbia characias was recognised as a group by the Graeco-Roman physician Dioscorides but he did not recognise it as a euphorbia. He had used that name for the succulent species of North Africa such as Euphorbia resinifera. Theophrastus had used the name 'Tithymalus' for the leafy Mediterranean spurges; Dioscorides followed this precedent.
Euphorbia characias grows all the way along the northern side of the Mediterranean Sea from Portugal to Turkey. It is a very variable species along this range in terms of the colour and shape of the nectar-secreting glands on the rim of the cyathium. These two characters are generally very consistent within Euphorbia species. Therefore, it was very tempting for the post-Linnaean taxonomists to give species epithets to the various combinations of colour and shape. In the end, the late and much missed, Alan Radcliffe-Smith recognised two subspecies. Euphorbia characias ssp. characias has dark purple to black nectaries that are weakly trapezoid in shape. Euphorbia characias ssp. wulfenii on the other hand has yellow nectaries that are crescent-moon shaped with distinct horns.
Subspecies characias tends to be found at the Western end of the range of the species while subspecies wulfenii tends to be found at the Eastern end. However where these ranges overlap all manner of combinations occur and some of these can be seen in the Order Beds at the Oxford Botanic Garden. In fact, even in 'the wild', the distinction has become very blurred and in western Portugal there is a large variation in the shape of the nectaries, and also the degree of pubescence on the leaves.
As result of the huge diversity in form and colour found in the wild, there has been an unnecessary rush to name garden variations and to give them cultivar rank. The problem with this is two-fold. Firstly, plants of Euphorbia characias can be notoriously short-lived at 5-7 years. This means that they need to be propagated vegetatively regularly, if they are to be preserved. Secondly, it is too tempting for gardeners and nursery growers to grow new plants from seed and cultivars of Euphorbia characias do not come true from seed. An undergraduate project 15 years ago revealed that none of the varieties in local garden centres were clones from the original plants.
Putting nomenclatural issues aside, Euphorbia characias deserves to be one of the most common plants in English gardens, producing a unique colour in April.
Turner R (1998) Euphorbias. Timber Press.
Walker T (2008) Euphorbias. Royal Horticultural Society.