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Euphorbia subgenus Euphorbia section triacanthium Jacobsen.
Part I

Euphorbia triaculeata 124-1999 sm

Rikus van Veldhuisen

Introduction
In this article I want to present to you a group of related species close to Euphorbia triaculeata.
These species have their natural habitat in North East Africa and the Arabian peninsula. They are characterized by a short thick mainsprout with many sidebranches, accordingly to the South African medusoid species. However this group of species possesses stipular spines, which are absent in the real medusoid species.
A second important characteristic feature in this related group of species is that the upper two of four spines are completely or partly fused to one spine. All species are highly appreciated by specialized growers of Euphorbias, however they can be very stubborn in cultivation.

The taxonomical place of the section Triacanthium in the genus Euphorbia.
The marking out of the family Euphorbiaceae as one family is in the last decade in botanical quarters not a subject anymore to heated discussions. Since the taxonomical review of Grady L. Webster (1994) of the University of California saw the daylight, is this classification of the higher taxa in the family of the Euphobiceae widely accepted.
It divides the Euphorbiaceae in five subfamilies. Namely Phyllanthoideae, Oldfieldiodeae, Acalyphoideae, Crotonoideae and Euphorbioideae. This last subfamily has our most interest and consists in five tribes, of which the tribus Euphorbieae is most important. On its turn the tribus Euphorbieae is divided in three subtribes; Anthosteminae, Neoguillaminiinae and Euphorbiinae.

There may be an agreement about the division of the higher taxa in Euphorbiaceae, this is certainly not the case in the lower taxa.

 
  E. sp. aff. triaculeata AJB D3 with two coloured cyathia
  Euphorbia species  aff. triaculeata AJB D3
  E. sp. aff. triaculeata AJB D3 shows variation in flowercolour.
  Euphorbia species  aff. triaculeata AJB D3
  A one year old seedling of E. sp. aff. AJB D3 showing the typical growth.

These lower taxa are successively dividerd in sections, subsections, genera, subgenera, species, subspecies, varieties and formae. Most discussion is about the genus Euphorbia, the Spurges, which contains by far the most succulent species and is of course best know by the lovers of succulent Euphorbias.
In the wellknown standardwork of Hermann Jacobsen (1977) the succulent species of Euphorbia are placed in three groups, namely the Pedunculacanthae, the Stipulacanthae and the Complex M. This last group, Complex M, contains the species originating from Madagascar. Appearantly he did not know exactly what to do with this species as it is a very variable group of species.
The Stipulacanthae, which are characterized by the possession of a stipular spine, are divided in four sections accordingly to the number of spines at each leafbase, in the case one; Monacanthium Chev., two; Diacanthium Boiss., three; Triacanthium Jacobsen and four; Tetracanthium Jacobsen.
As one might notice is the making of a botanical classification a job for anyone who can count the fingers on one hand. Putting a particular species in a certain section might prove to be a bit more of a problem. So has the species Euphorbia monacantha given its name to the section Monacanthae and was originally put into this section. However E. monacantha is much more closely related to the species of the section Triacanthium. So this species and E. immersa are put into the latter section.
The remaining species in the section Monacanthae, with its most wellknown species E. venenifica, are most questionable if the belong at all in the the group of Stipulacanthae and are perhaps best placed in a group of her own.
The section Triacanthium is not a homogeneous group of species, but can be divided in two parts. One group has a more southernly distribution area, concentrated in Kenya and are lacking the short, thickened mainstem. This species, most wellknown species like Euphorbia similiramea and E. glochidiata, I will exclude from this article.
The group of species treated here are Euphorbia monacantha ( most known by its name, but in my opinion not in cultivation today), triaculeata, schizacantha, xylacantha, immersa, actinoclada, kalisana, awashensis, erigavensis, margaretiae, myrioclada and the most recently described godana. Moreover I want to present to you two forms, which are in cultivation, namely E. species nova Mrs. Ash and E. species 732.


 

 

 

 

 

Sceme 1.
Classification of the higher taxa of the family Euphorbiaceae.

Family
Subfamily Tribes Subtribes Group Section
           
Euphorbiaceae
Phyllanthoideae
       
  Oldfieldiodeae
       
  Acalyphoideae
       
  Crotonoideae
       
  Euphorbioideae
Euphorbieae
Anthosteminae
   
      Neoguillaminiinae
   
      Euphorbiinae
Pedunculacanthae
 
        Complex M
 
        Stipulacanthae Monacanthium
          Diacanthium
          Triacanthium
          Tetracanthium




  Euphorbia species aff. triaculeata   Euphorbia species aff. triaculeata  

 

Euphorbia sp. aff. triaculeata. This form with an unclear relationship form a untidy shrub.

Photo: Guiseppe Orlando.

 

This habitat picture is showing a plant fitting well in the original description of E. triaculeata.

Photo: Giuseppe Orlando.

 

Euphorbia triaculeata Forskall.
Since the section Triacanthium thanks its name to euphorbia triaculeata and furthermore the first species was to be described, it is obvious we start the dealing of each specie with this one.. As early as 1775 she is described by Forskall on basis of plants origaniting from the 'Çosta dei Miguirtini', nowadays better known as Somalia. Susan Carter (1987) states that the identity of E. triaculeata is no problem and that it is still growing on the typelocality, near the shore of the Red Sea of the Arabian Peninsula. Besides she mentiones that appearently in the nearby Djibouti the same species grows. This article is supplied with a nice habitat picture of this species made in Djibouti. These plants are striking, about half a meter high, sprouting from a depressed mainstem with sidebranches which form an angle of approximately 45 degrees with groundlevel. In the accompanying text we find a description of the plants; about half a meter high, sidearms are 1 to 1,5 centimeter thick, 3 to 5 ribs and the spines stand on arched podaria. In an article from Rauh (1966) we find another habitat picture with plants on it with the same habitus. However I don't know any plants from the typelocality I take Euphorbia triaculeata to be big plants (0,5 meter high), having these straight sidebranches with the constant angles and the waving ribs (arched podaria).
Plants found by Schweinfurth in Eritrea on the flats west of Massana are described by Pax as Eunphorbia infesta. These plants are taken not to be different from E. triaculeata and so E. infesta is synonymous. Other plants found on some islands in the Hamfila Bay before the coast of Eritrea were described by Ehrenberg as Euphorbia triacantha and later degradated by N. E. Brown as a variety under E. triaculeata.

Euphorbia species affinis triaculeata    
Grafted cutting of E. sp. affinis triaculeata collected by Frans Noltee in Yemen    
Euphorbia species affinis triaculeata    
E. sp. aff. triaculeata from Yemen, grown from a cutting taken at the cut-two-times method. It is not 10 centimeters high. This represents the form which originally came from Eastern Europe.    
In our collections there are several forms running around labelled as Euphorbia triaculeata or E. species affinis triaculeata. Most of them have an unknown origin or at least insecure, but in my opinion the real E. triaculata, with the above mentioned identifying features, is rather scarse. Of all the plants with this species name I came across in some 20 years, plants with the collectionnumber AJB249, collected south-east of Hays on the Tihama plains, Yemen, did match them the most. This collection has also the thick more than 1 centimeter thick branches with the arched podaria on which the spineshields are placed. The cuttings I once grew in my collection did rebranch quite frequently and strikingly these sidebranches formed the above mentioned angle of 45 ° and went on growing rather straight, when not disturbed and do not curve into a vertical position.
Recently plants were sold by Ernst and Maritta Specks as E. triaculeata and this rooted cuttings do match the plants of AJB 249 quite well. Have acquired this plant just recently and not knowing its flowers or where it comes from I cannot say much more about it than that similar plants ware also distributed by Chuck Hansen in the United States.
Alan Butler, who collected AJB249, made at least two other collections, designated as Euphorbia (species affinis) triaculeata, which are numbered as AJB D3 and AJB D10. Both do have much thinner branches.
Euphorbia species affinis triaculeata AJB D3 is collected south of Djibouti-town. In crosssection branches are circular and the green is slightly marbled with stripes of lighter green. The flowers are very showy and coloured bright red and yellow.
Like most, if not all, species in this group is E. species affinis triaculeata AJB D3 selffertile and seedlings do form the thick depressed mainsprout. Although sowing is the best way to get a plant with the natural habit, there is also a vegetative way to achieve this.
Once a branch is rooted it is best to cut off the upper part of it. It is forced to produce sidebranches if it wants to grow further. If you are lucky enough this sidebranches show the characteristic features of a thick short mainsprout. When big enough these sidebranches can be cut off again and rooted. This socalled cut-two-times method can supply you with plants with natural habit.
Euphorbia species affinis triaculeata AJB D10 and also E. species nova Lavr. 13176, Djibouti, will be discussed under the newly described Euphorbia godana.
I grow two different clones of different origine, which are both labelled as Euphorbia triaculeata, Yemen. One is a gift of a friend from Slovakia and the other one is collected by Frans Noltee. Unfortunately both have lost other data on locality or collectionnumber.
The one from Slovakia is a very weak form and the slightly marbled sidebranches do make the vertical curve upwards on plants with the original mainsprout.
The one collected by Frans Noltee is somewhat thicker and the spimeshields are placed in ribs and on an elevated foot. Between the ribs is a lightgreen stripe and all in all I think this is one of the most handsome forms of all dealt with here.
Overseeing all these forms one can say that many things still needs to be sorted out and a lot of research in the field needs to be done before a scientific satisfactory solution is found for all relationsship and their taxonomic places are filled in. Putting all the weaker forms in the variety triacantha seems on material availlable in cultivation to easy.

 



 

 


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