Guest column by Theo Heijnsdijk
(Translation and habitat pictures by FN)
History
In 1812 Adrian Haworth in his “Synopsis plantarum succulentarum” described a new genus in the family Euphorbiaceae: Dactylanthes, translated by himself as Finger-flower. He distinguished four species in the genus: D. patula, D. anacantha, D. tuberculata and D. hamata, characterized by the finger-like lobes of the inflorescences.
In 1823 he added a fifth species: D. globosa. In the description, he reported that he had seen the species in bloom in Kew in October of that year.
Fig. 1
In 1826, Curtis’s Botanical Magazine published a coloured plate (plate 2624, see figure 1) with a detailed description by John Sims. This time under the name Euphorbia globosa, which is now generally recognized. The genus Dactylanthes has thus merged into the genus Euphorbia. The species D. anacantha and patula are seen as synonyms of Euphorbia tridentata by current botanists. For the other three, the specific name has remained the same.
Habitat
This distinctive plant seems to have been widely distributed in the Eastern Cape area of South Africa*, but nowadays the species is much rarer. It occurs in the area between Port Elizabeth and Uitenhage where it grows on low stony hills up to 20 km from the coast.
On the Red List of South African plants, the species has the status ‘endangered’. According to that report, it is known from less than 5 localities. The plant is listed in Appendix 2 of CITES.
* In the famous work “The succulent Euphorbieae” (1941), by White, Dyer and Sloane, we find (among many other things) the following observation on this topic:
“E. globosa is abundant in the karoid scrub between Uitenhage and Port Elizabeth, sometimes forming uniform mats of the dwarf branch-tips in such masses that it is difficult for the passer-by not to tread on them.”
Description
It forms compact clumps up to 8 cm high and to 50 cm in diameter, consisting of globular** stem segments that seem to be connected in a rather random way.
** Hence the name globosa (= spherical).
The young shoots bear small scaly leaves which later disappear. The oldest segments are grey to almost white.
African names for the species are eierpol, knopmelkbol and langbeentjie.
A mature segment develops a thin stem that bears the inflorescence, which is supported by 3 bracts. When the inflorescence or fruit has dropped, the flowering stem often divides again into 1, 2, or 3 new stems which like the older ones may become about 8 cm long.
Fig. 2 shows the scar of the dropped inflorescence, and it is also visible how 2 new stems develop alongside. At the bottom, the third one just starts. A trichotomous division I would say. In this way, a cascade of stems is created. The dried flower stalks remain on the plant. White, Dyer and Sloane have the following comment on the species:“Much has been witten about E. globosa since 1826, yet its “singularly whimsical growing habit” remains as fresh a source of surprise to-day as ever. In its native surroundings the globose branches form thick mats, closely pressed to the ground. These branches are gradually drawn down almost perpendicularly underground, new branches replacing them at the surface, and these take their turn for a while at putting forth the characteristic cyathia and cymes, on peduncles which are variably very short or almost absurdly long. Under cultivation the branches are rarely drawn underground, but they pile up in a fantastic medley, each branch differing somewhat from the others in shape, globose, clavate or cylindric, so that a large potted plant looks not unlike a bowl of quaint, irregular marbles or tangled strings of misshapen large beads. Occasionally the longer peduncles produce little new branches up aloft, instead of the expected inflorescence, until of their own weight these adventitious newcomers drop over to the ground, send out rootlets and begin life on their own accord.”
Inflorescence
Here I would first like to discuss the special inflorescence of Euphorbias. What we see as a flower is in fact a whole bouquet. Each stamen is a separate male flower stripped of all non-essential parts. Only the stamen itself, ending in 2 anthers, is therefore left. In the same way, the pistil is in itself a separate female flower. Pistil and stamens grow from a kind of cup, called involucrum. On the outside of the involucrum there are usually 4 or 5 nectar glands. All those basic flowers, together with what is around them, form what an ordinary plant enthusiast sees as ‘the flower’. But in botany, this combination of flowers is called a cyathium.
In figure 3 we see a young stage of the very special inflorescence of E. globosa. In the middle you can see the pistil with the 3 stigma lobes and around it the anthers in an immature stage. The diameter of this inflorescence at that time was 10 mm.
If you look at that picture you will immediately understand why Haworth chose the name ‘Dactylanthes’ (finger-flower) for this type of plant.
The ‘fingers’ are outgrowths of the nectar glands. The nectar is secreted by the wart-like elevations. In E. globosa we usually find 3 or 4, sometimes 5 ‘fingers’ per nectar gland.
In figure 4 we see an inflorescence at a much later stage. The pistil has reached its final size and the stigma with its 3 lobes sticks out between 2 fingers. The swollen ovary is clearly visible. At the bottom left of the cup we see 2 immature anthers and at the top right a stamen with 2 ripe, pollen producing anthers. If you look closely, you can see about halfway up this stamen, at the level of the cup edge, a kind of ring around the stamen. That is the transition from flower stalk to stamen. When the stamen (= flower) has finished flowering, it drops off its flower stalk. What remains is a kind of hollow tube. In the cup we also see a number of flower stalks from which the finished stamen has already broken off. On the 3 fingers of the honey gland at the bottom right, we see a few of those broken stamens.
A peculiar thing in the photo is that at the upper nectar gland there were first 3 fingers of which the middle one has divided again halfway.
It is reported that at the ends of the flowering stems sometimes not cyathia, but small spherical sections develop. If the stems bend due to the weight of the segments and touch the soil, they will quickly take root.
In cultivation
I bought my oldest E. globosa around 1990 at a cactus market. It was probably already a slightly older plant, consisting of some larger gray-white balls, and I wondered if it had been imported. This plant has now grown into a collection of perhaps 70 stems, covered with a tangle of dried flowering branches which makes it impossible to make a nice photo of it. This plant is self-fertile. Usually, after flowering, the fruits with 3 fertile seeds -characteristic for Euphorbias- appear .
In figure 6, we see seedlings of 5 months old in a pot.
In figure 7, photographed when the same seedlings were 4 months old, it can be seen that one of the plants in the same pot is already preparing to flower.
Euphorbia globosa requires a sunny place with not too much water. If not, the spheres lengthen, and the plant will look like the closely related E. ornithopus.(The same group also includes E. tridentata, E. polycephala, E. wilmaniae and E. planiceps).
Minimum temperature in winter 8 ºC, although in literature it is reported that the plant can withstand frost.
Finally
In a series of articles about the plants grown in the botanical garden in Geneva, Alphonse de Candolle wrote an extensive article about E. globosa in 1836. There was a beautiful folding plate in which all parts of the plant were depicted in detail. See below. Unfortunately, the scan is slightly distorted on the left-hand side.
Literature
Buddensiek, V. (1998). Sukkulente Euphorbien; 25, 101.
Candolle, A. P. de. (1836). Septième Notice sur les Plantes rares cultivées dans le Jardin de Genève, Memoires de la Société de physique et d’histoire naturelle de Genève 7 (2): 288 – 293, fig. 5.
Haworth, A. H. (1812). Synopsis plantarum succulentarum: 132.
Haworth, A. H. (1823). Plantae rarae Succulentae; a Description of some rare Succulent Plants, The Philosophical Magazine and Journal 62: 382.
Sims, J. (1926). Euphorbia globosa, Curtis’s Botanical Magazine 53, plaat 2624.
White, A; Dyer, R.A. and Sloane, B.L. (1941). The succulent Euphorbieae (Southern Africa).