Euphorbia eyassiana - Cactus Club

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Euphorbia eyassiana

Plant of the Month > Species E to F

by Bruce Brethauer

       While preparing this article, my research uncovered a few surprises on the identification this plant. I originally acquired my plant from Bill Hendricks in 2012; he identified it as Euphorbia nyassae. The first volume of the Euphorbia Journal illustrates a plant which is identified as Euphorbia nyassae, and which appears to be a dead ringer for my plant, but in the second volume of the Euphorbia Journal (Editors' Notes Volume 1) the identification of that plant was changed to Euphorbia eyassiana. Apparently, this clone was originally collected by P. R. O. Bally who sent it to the International Succulent Institute (ISI), which distributed this plant under the name of Euphorbia sp. aff. nyassae. Over time, the "sp. aff." portion of the name was dropped, and this clone was erroneously identified as "E. nyassae". The true Euphorbia nyassae is discussed and illustrated in the Euphorbia Journal (Volume 3, pages 48, 49), and while being similar to this plant, there are also significant differences. A brief discussion and several habitat photographs of Euphorbia eyassiana are included in Volume 8 of the Euphorbia Journal (pages 63, 64 and 65). The description and images of this plant convince me that my plant is this species rather than E. nyassae, so I have restored what I believe its original identification had been ("Euphorbia sp. aff. nyasse"), as well as its most likely identification as E. eyassiana.

          Euphorbia eyassiana  is one of a number of Euphorbia species from the Great Rift Valley which produces a mounds of thin, clustered, four angled, branching stems. This species distinguishes itself from a number of similar species by spreading from a  rhizomateous rootstock, producing thickets which may spread to several feet or more in habitat. The branching stems are 4-angled, about the diameter of a pencil, and can grow to heights just under 3 feet (the plants which I have seen in cultivation are typically much shorter; frequently growing to about a foot or so in height). In lower light, the central portions of the stems are colored a pale green, with darker green stripes at the stem angles. In very bright light, or when the plant is heat or drought stressed, the stems tend to take on more reddish hues. 4 needle-like and spreading spines are produced on each spine shield. The uppermost spines are significantly shorter, and the lower pair are longer. The flowers (cyathium) are minute - only about 2 millimeters across, and have orange to reddish colored glands

           Euphorbia eyassiana originates from near the shores of Lake Eyasi in Tanzania, and into the adjacent region of the eastern Serengeti plains. Susan Carter Holmes relates that this plant, while fairly common throughout its range, has a rather narrow distribution. It is allied to a number of similar looking euphorbias  (with slender, square stems, and bearing 4 spines per cluster) from the Great Rift Valley, including E. isacantha, E. tetracanthoides, and E. schinzii, but according to Susan Carter Holmes, it is actually only distantly related to Euphorbia nyassae.

           This is a remarkably easy plant to grow and propagate. It responds extremely well to my general guidelines on growing cacti and other succulents, and does especially well when grown outdoors exposed to full sun and high summer temperatures. Given this treatment, and provided with relatively moist conditions during this growing season, and this plant will produce remarkable growth (the pictured plant shows only one year's growth, from a few small rhizomes and a tiny section of two stems). This species seems to be more widely grown in Europe where it has gained a reputation for being more tolerant of the European climate than other Euphorbia species from the Rift Valley. It is readily propagated from stem cuttings and sections of rhizomes; I suspect that it can readily be propagated from seed (it is a reliable bloomer, and I suspect that it is capable of producing viable seed when it is selfed).

           I found out quite by accident that this species (or at least my clone of this plant) has remarkable cold tolerance. When moving my plants back indoors for their winter dormancy, my plant fell from my outdoor bench and spent the entire winter of 2012/2013 unprotected in my vegetable garden, where it was exposed to extended periods of sub freezing weather, and temperatures down to approximately 5 degrees Fahrenheit. While this plant took considerable damage from the cold, some of the roots and a portion of one or two of the stems managed to survive. While I would not promote this plant as a candidate for the winter hardy succulent garden here in Ohio, properly sited in a warm microclimate, and shielded from excessive winter moisture, this plant may prove to be root hardy to a zone 7. In spite of its extreme cold hardiness, I do not recommend that this plant should be subjected to sub-freezing temperatures, as the stem tips will invariably suffer from some degree of frost damage and subsequent die back.

           In spite of its relative ease of culture, and rapid growth rate, this plant is not frequently known and grown - compared to several other species this plant has a rather coarse and common appearance, and many people feel it has a rather weedy look - its stems lack the beautiful blue green coloration of of E. greenwayi, and its spines do not have the colorful interest of E. aeruginosa. Still, this plant does have a few growers who maintain it in their collections, and it probably deserves to be more frequently grown. I will leave it to others to test it for its suitability in the garden, as I feel that it may prove to be hardy enough for zone 7 succulent gardens.

           While this species is not new to cultivation, it is never common, and is seldom offered from the usual mail order nurseries under either of the two names I have given here (I have not succeeded in locating a grower who currently offers this species for sale). Thanks to the generosity of Bill Hendricks, I suspect that some members of the Midwest, Greater Pittsburgh, Michigan, and The Central Ohio Cactus and Succulent Societies may grow this clone. If my guess about the ultimate source of this plant is correct, the ISI may also continue to propagate this clone. Should there be any demand for additional plants of this clone, I'm sure that these could be propagated by a number of individuals.

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