March 2021 - enjoysucculents

Drosanthemum albiflorum

Although the specific name means “with white flowers”, it is not uncommon to come across plants of this species with light to dark pink flowers.
They form erect, much-branched shrublets to 15 cm tall, with leaves that are 7-10 mm long and 4 mm thick, round in cross-section, and with a blunt tip.
Between August and November, the plants produce their flowers at the tips of the branches; they are up to 17 mm in diameter.
In certain parts of the distribution area – stretching from Matjiesfontein to Robertson and Riversdale – the plants grow in abundance.

Euphorbia grandicornis (Guest column by Theo Heijnsdijk)

Name
Euphorbia grandicornis is a representative of the large group within the genus of shrub-like succulents with spine pairs, also referred to as the diacanthium section. Plants belonging to this group usually have 2 spines that are facing outwards from the edge of a shield. Another example of a member of this group is E. canariensis. Sometimes there are 3 or 4 spines and sometimes only one (for example, in E. unispina).
Grandicornis literally means ‘with large horns’.
In English-speaking countries, the plant is also called ‘Cow’s horn Euphorbia’. The thorns remind me more of the tentacles of a snail. See Fig. 1.

In the next image, we see (between the spines) the scars of the tiny leaves that are formed in the new growth and that will soon turn yellow, shrivel, and fall off.

Other names that are widely used are ‘Big horned Euphorbia’, ‘Rhino thorn’ and even ‘Zig-Zag Cactus’. There is also a cristate form and this looks even much more ferocious than the normal plant. In Afrikaans, the plant is called renosterdoring (a renoster is a rhinoceros and doring stands for thorn).

History
The plant has probably been in cultivation for quite a long time, but for many years it went undescribed.
We first come across the name Euphorbia grandicornis in 1889 in the first part of the 2-volume book ‘Pflanzenbiologische Schilderungen’ by the German professor of botany dr. Karl Immanuel Eberhard Ritter von Goebel. In a general story about Euphorbias, he discusses a number of aspects of E. grandicornis as if it were a well-known plant. It is nothing like what we mean by a description nowadays. However, we do find a beautiful pen drawing of a top cutting (Fig. 3).

In addition, there is a drawing of the leaves in the new growth and of a cross-section of the trunk in which the peculiar, twisted shape of the winged ribs is clearly illustrated (Fig. 4).

Von Goebel reports that he has not been able to find any data on the habitat. However, from the physical appearance of the plant with the wide thin ribs and therefore a large surface area – similar to, for example, leaf cacti- he concludes that it is unlikely to be exposed to long dry periods in its natural environment.
After von Goebel it was quiet until 1893. In that year, an article by a Mr. J.E. Weiss, Reader in botany, appeared in the periodical ‘Dr. Neubert’s Deutsches Garten-Magazin’ under the title “Empfehlenswerte Cacteen” (“recommendable cacti”). He took the concept of cactus rather broadly because the last ‘cactus’ discussed in his article is Euphorbia grandicornis. There is even a photo, the very first one published, but the print quality was rather poor in those days (Fig. 5).

Original description
The plant was still not officially described at the time. That was done in 1897 by Nicholas Edward Brown in part 26 of Hooker’s Icones Plantarum. That is why the author’s citation which is always added to the species name in scientific literature, in this case is ‘Goebel ex N.E. Br.’. The description by Brown, who was employed by Kew Gardens near London, was based on a plant that had been cultivated there since 1876. The description with Latin diagnosis was accompanied by two drawings of quite a big specimen. I don’t particularly like these drawings. Brown also mentioned a locality: South Africa, Umfolosi River, Zululand.

Habitat
Nevertheless, there was apparently uncertainty as to where the plant occurred in nature, because in 1904 in Engler’s ‘Botanische Jahrbücher’ ( ‘Botanical Yearbooks’) in a monography on Euphorbia’s in the section Diacanthium the author, F. Pax, writes: “Vaterland unbekannt, vielleicht Africa” (Native country unknown, maybe Africa). And in 1907 Alwin Berger in his ‘Sukkulente Euphorbien’ says: “Homeland ?” and further down:
The origin of the plant is unknown. However, it is not plausible that it was only recently introduced, because the large specimen in Kew mentioned above, indicates that it is an old inhabitant of our greenhouses.). Brown and others later compiled the part about the Euphorbiaceae in Sir William T Thiselthon-Dyer’s ‘Flora Capensis’. This part appeared in 1915 and here E. grandicornis is also treated. The last line I find quite funny: “Distribution: Easter Region: Zululand, stone! Marriott! And cultivated specimens!”.
I suspect Marriott is a name, but I haven’t been able to find any information. But especially all those exclamation marks intrigue me. I have no idea what the writer wanted to emphasize with this.
In modern literature, it is made clear that the range is quite large: South Africa (Kwazulu-Natal), Swaziland, Mozambique, Kenya. There the plants grow at low altitudes (up to 400 m) in small groups between grass or shrubs. They have 3 or 4 ribs and can be up to 2 m tall. It seems that large plants often succumb to their own weight. The variety sejuncta (described in 1970 by Leach), which remains smaller and sometimes grows lying down, has 2 or 3 ribs and is known only from a site in Mozambique. There it grows in the company of Aloe chabaudii, Euphorbia corniculata and E. tirucalli on granite slopes at altitudes between 380 and 700 meters.

Flowering
In a sunny location, a plant that is preparing to flower stands out because of the vivid red colour of the developing cyathia (Fig. 6).

These appear on the uppermost and therefore youngest, segments of the stems. There are always 3 cyathia together, but often only the middle one will fully develop. It only produces male flowers (stamens). The two outer cyathia are bisexual. First, the male flowers develop (Fig. 7)

and when they dry out, the female flower (pistil, fig. 8) follows.

All cyathia are bright yellow in colour. This type of inflorescence with a central male inflorescence flanked by 2 bisexual cyathia is often found in Euphorbias, for example in E. canariensis.
Ripe fruits are about 8 mm in diameter and purplish-red in colour (Fig. 9).

Fruit formation in a E. grandicornis in Jan Celliers Park (Pretoria, South Africa). Photo Dr. Johann C. Knobel.

Cultivation
A well-drained mixture with little organic material and a lot of additions such as lava, pumice, clay chunks, etc. is recommended. It’s best not to use peat. Give ample water from March to September. In winter, the temperature should be at least 12 °C, but preferably a little higher. Propagation is by cuttings, which root quite easily, or by sowing. Seed is fairly well available and it is fascinating to see how a wildly thorned plant develops from the delicate seedling with its 2 cotyledons (Fig. 10).

In frost-free areas, E. grandicornis is recommended for hedges. Pruning is well tolerated. Goats eat the corners off but leave the thorny sides alone. The juice doesn’t seem to hurt them.

Literature:
Berger, A. (1907). Sukkulente Euphorbien: 52-53.
Brown, N.E. (1897). Hooker’s Icones Plantarum 26, plates 2531, 2532.
Brown, N.E.; Hutchinson, J.; Prain, D. (1915). Euphorbiaceae in Thiselton-Dyer, Flora Capensis 5, sect 2, part 2: 367-368.
Goebel, K. von (1889). ‘Pflanzenbiologische Schilderungen’ 1: 62-63.
Pax, F. (1905).. Monographische Übersicht über die afrikanische Arten aus der Sektion Diacanthium der Gattung Euphorbia in Engler’s Botanische Jahrbücher 34: 74.
Weiss, J.E. (1893). Dr. Neubert’s Deutsches Garten-Magazin 46: 291.

First published in Succulenta 92 (4) 2013. Translation from the Dutch by F.N.

Didierea madagascariensis (sogno)

Of the two species of Didierea (the other one is D. trollii), this is by far the most widespread and best-known. It occurs abundantly on red sandy soils in SW Madagascar, from the dry spiny bush in the Toliara area northwards to the Morondava river.
D. madagascariensis has quite a distinctive growth form: the single trunk is up to 0.5 m thick and 6 m or more tall; it is generally unbranched up to 2 m high.
The branches usually grow more or less upright and are often curved towards the top; the short lateral shoots give rise to clusters of very long spines (up to 12 cm) and groups of short-lived, greyish green and narrow leaves (7-15 cm long and 0.3-1 cm wide).
The inflorescences may cover extensive areas of the upper branches. The numerous unisexual flowers are pale yellowish to greenish-red and open only during sunny weather between 10 am and 2 pm to be pollinated by bees.
In cultivation, the plants are often propagated by grafting a short-shoot on a strong plant of Alluaudia procera, thereby producing nice specimens within 3 to 4 years.

Crassula multicava (Guest column by Theo Heijnsdijk)

Crassula multicava (Fig. 1) is a sparsely branched plant with fleshy stems up to about 30 cm long and. 1 cm thick. Long stems lie down and form new roots as well as branches from the leaf axils. The leathery leaves are up to 6,5 cm long and 4 cm wide. Towards the stem, each leaf narrows down to a petiole (leaf stalk), which is fused with that of the opposite leaf, giving the impression that the stem has grown through them.C. multicava occurs in South Africa (Mpumalanga, KwaZulu-Natal, Eastern Cape) and was described by Lemaire as early as 1872. Multicava means: with many cavities. This refers to the upper side of the leaf, which is littered with many round dimples, somewhat like an orange (see Fig. 2 below),

(giving rise to the name ‘Pitted Crassula’. The dimples are so-called hydathodes, a name for glands that can excrete moisture. Such glands occur in many plant genera, and they can be of different anatomical origins. In Crassulas, they are converted stomata. As a rule, hydathodes are intended to get rid of excess moisture, but that sounds rather strange for succulents, who need to lose as little moisture as possible. Gordon Rowley in his book ‘Crassula’ suggests the possibility that during the day when temperatures are very high, air bubbles are formed in the vascular system of the plant so that the juice flow is blocked (embolism), comparable to air bubbles in a garden hose. At night, the plant would then supply extra water from the roots, thereby increasing the pressure so that the air dissolves back into the plant juice. Then the excess water must evaporate again via the hydathodes. Rowley invites readers to come up with a better theory.

In a shady place, the leaves are fairly light green (Fig.3 above).
In a sunny position, they stay smaller and are much darker green with the leaf edges and hydathodes turning brownish-red. By the way, in dappled shade, they also grow better than in full sun. In Afrikaans, the plant is not called ‘skaduplakkie’ (shadow crassula) without reason.

My first introduction to the species was during the Christmas holidays of 2005, when I stayed on the Canary Island of Gomera. I went for a walk near the apartment and came across a garden in which the soil was covered with a layer of perennial succulents with lots of pink flowers. By the way, the plant had not kept to the boundaries of the garden. Of course, there was no name sign. In May 2008, I saw the plant for a second time (now properly labeled), as a ground cover in a bed with other succulents in a greenhouse of the Botanical Garden of Berlin.

In my greenhouse (in the Netherlands) the plant blooms abundantly from March /April until well into autumn. The flowers are rather loosely arranged in the inflorescence, which results in a somewhat unkempt look. (Fig. 4 below).

It reminds one of a cloud of mosquitoes and I think that is why the plant is sometimes called the ‘Mosquito Flower’ in America.
Crassula flowers perfectly conform to the prototype of a flower as you find in, for example, a biology book for schools. From the outside going to the centre, one first comes across the calyx leaves, then, alternating in position relative to these, the same number of petals, then alternating again, the same number of stamens and lastly, in alternating position again, the same number of pistils on top of the ovary. Such a flower structure with all this in equal numbers is called isomerous. With most Crassulas, the flowers are 5-merous, so 5 of all the above parts, but in C. multicava the flowers are usually 4-merous. They are white inside and pink on the outside (Fig. 5).

The appearance of the star-shaped pink flower is the reason that the plant is called ‘feetjie plakkie’ or ‘feetjie crassula’ in Afrikaans. A feetjie is a fairy in English, so there it becomes fairy crassula. In Australia, the plant is called ‘London Pride’, because the plant in flower resembles Saxifraga ‘London Pride’, used as a ground cover in England. By the way, ‘London Pride’ is also the name for a multi-award-winning English beer variety.

Due to the large number of flowers, the flowering stems bend to the ground. By the time the flowering season ends, miniature versions of the plant (called bulbils, see Fig. 6 and 7 below) appear here and there on the flower stalks.

This is quite normal for some Kalanchoes (Bryophyllums), but exceptional in the genus Crassula. These plantlets easily become detached from the mother plant and then quickly take root. This way, in a suitable climate such as in the Canary Islands, the plant can become a pest. The name ‘Cape Province Pygmy weed’ also refers to the rampant character. I don’t know what it has to do with pygmies, but maybe it only refers to the small size of each plant.

The regenerative capacity of C. multicava is phenomenal. As early as 1938, a scientific paper was published describing how new plants can emerge from epidermis cells of small cut-off pieces of leaf. In these times of tissue culture, this may not sound so spectacular, but at the time it was considered a unique trait.
Rowley attributes the great regenerative capacity and the forming of bulbils to the large number of chromosomes of C. multicava. As we know, almost all hereditary information of an organism is recorded on the chromosomes, which are located in the nucleus of each cell. In general, in a nucleus there are 2 sets of chromosomes, 1 set originated from the father and 1 set from the mother. This is called diploid and the number of chromosomes is then indicated as 2n. The number of chromosomes in a set is indicated by the letter x. Normally, x = n. For a fruit fly x = 4 applies, for a human x = 23, for a guinea pig x = 32 and for most Crassulas x = 7. A human being has 2n = 2x = 46 chromosomes. In some species there are more than 2 sets and such a cell is called polyploid. In plant species that are normally diploid, polyploidy often leads to larger individuals or larger flowers. In Crassula, no less than 44% of the species are polyploid. The champion is C. spathulata with 2n = 20x = 140, which indicates 20 sets of 7 chromosomes per cell nucleus. C. multicava comes second with 2n = 16x = 112, so 16 sets.
I must admit that the link between a high number of chromosomes and a high reproductive capacity is not clear to me. Of other polyploid Crassulas it is not recorded that they reproduce so easily and neither do they do form bulbils, whereas C. cordata, which does make bulbils, is just diploid. Maybe someone should come up with a better theory here, too.

As for cultivation: frost-free, although they seem to be able to endure a single bit of frost without damage. Otherwise indestructible. The plant also grows well in shade.

There is a subspecies, C. multicava subsp. floribunda. This one is a bit more robust in all parts and the flowers are 5-merous. It has a cultivar, C. multicava subsp. floribunda ‘Panache’, in which the edges of the leaves are whitish-yellow. C. multicava subsp. multicava, on the other hand, has a forma ‘Variegata’ in which the leaves are green at the edges but yellow in the centre.

Literature:
Harders, C.L. (1932). Crassulaceae, Succulenta 15 (11): 207.
Rowley, G. (2003). Crassula, Cactus & Co.
McVeigh, I (1938). Regeneration in Crassula multicava, American Journal of Botany 25: 7 -11.

First published in Succulenta 90, (1) 2011. Translated from the Dutch by FN.