Euphorbia x PasteuriiDon Witton

Euphorbia x pasteurii has only been on the garden scene for about four years so it is a fairly new plant name to most gardeners. However, from my experience the plant which now possesses this name has caused much confusion amongst keen plantsmen.

Many people will know of the Honey Spurge – E. mellifera, an evergreen shrub from the Canaries whose flowers exude a sweet honey smell. Regarded by some to be not fully hardy (its AGM award is accompanied with an H3 rating for hardiness – H4 being fully hardy), it has taken -13C for me in the past with relatively minor frost dieback on the plant.

A much rarer but botanically related species which hails from the Azores is Euphorbia stygiana, a more thicket forming shrub rarely exceeding 3′ in this country and often wider than it is tall. The evergreen foliage is similar in shape to mellifera but is wider and the colour is a deeper green. In my experience E. stygiana does not perform as well as mellifera in British gardens.

At Oxford Botanic Garden these two plants were grown sufficiently close together for them to hybridize which was initially not thought possible and this is where the confusion started. Plants raised from stygiana seed were passed to gardeners including myself, and the HPS conservation scheme also distributed stygiana seedlings around the country. Many of these plants were hybrids. I have propagated cuttings from my original plant and sold them for about three years as stygiana, but it clearly now is not. As it gradually became apparent that seedlings had hybrid vigour a temporary name was given as E. stygiana ‘Devil’s Honey’ (the flowers still have the honey scent). This has confused matters even more and I have written to the Plant Finder to say that this is now an invalid name, but I see that it is still listed in the current volume.

Eventually it was decided to do some DNA work on the hybrids at Oxford University. A student called George Pasteur did the research work and concluded that hybrid plants were roughly 50% each of mellifera and stygiana. The plant was consequently named after George and has been registered as such.

Euphorbia x pasteurii is a great garden shrub resembling a classy dense rhododendron in leaf but with yellow honey scented flowers from April to June. I think it makes a better garden plant than either of its parents and it is fully hardy for me. You will need to give it space — my plant is currently 8′ tall and a similar distance across the base although it can be pruned to keep it smaller.

So if you have acquired E. stygiana from me or any other source and it is a strong growing shrub taller than 3′, change its name but keep enjoying its display throughout the year. Some of the feedback I have had from people who have acquired the plant from me include ‘a fantastic plant at the bottom of my garden’ and ‘who cares what its name is, it’s a wonderful evergreen shrub and the flowers in spring are a bonus’.

First published in the South Pennine Group Newsletter, Winter 2007
and subsequently in Cornucopia Issue 23
© Copyright for this article: Don Witton

This article was taken from a copy of Cornucopia that was published in 2009. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.