Monadenium
Monadenium is a group of East African succulent spurges — members of the vast family Euphorbiaceae — that gardeners once treated as a genus in its own right but which botanists now fold into the giant genus Euphorbia. Whatever name is on the label, these are tough, characterful plants: knobbly or ridged succulent stems topped with curious little floral structures whose fused, tubular bracts and single horseshoe-shaped nectar gland set the group apart from most other spurges.
Taxonomy
Monadenium was described in the 19th century for a set of succulent spurges distinguished by the structure of their cyathium (the false flower typical of the whole family) — in particular the fusion of the nectar glands into a single gland, the feature that gives the group its name. Modern molecular work has shown that these plants sit inside Euphorbia rather than beside it, so the name has been sunk into that genus and the species transferred across. In everyday horticulture, however, the old combinations persist on countless labels and in the nursery trade — you will very often see a plant sold as Monadenium when its accepted name is now Euphorbia. Both usages refer to the same plants; this page keeps the familiar horticultural grouping for convenience.
Description
The plants grouped under Monadenium are succulents, and the group is diverse in form. Many make thick, fleshy, cylindrical stems patterned with spiralling rows of low tubercles, giving a knobbly or braided appearance; some are shrubby and branching, others form low clumps, and a number grow from a swollen underground caudex or tuberous rootstock, sending up soft annual or semi-succulent shoots. Leaves, where present, are usually held near the stem tips and are often shed in the dry season.
Like all spurges, they do not bear ordinary flowers. Instead they carry a cyathium — a cup-like false flower — and it is the structure around this that gives the group its identity: the bracts are fused into a distinctive tubular, forward-curving cup, often flushed pink, green or reddish, and its nectar glands are merged into a single horseshoe- or shoe-shaped gland — the feature that gives the group its name. As with the rest of the family, all parts exude a milky latex when cut.
Distribution
The group is centred on tropical and subtropical East Africa, with the greatest diversity in Kenya, Tanzania and neighbouring countries, extending into parts of central and southern Africa. Plants grow in seasonally dry bush, rocky slopes and open woodland, where they endure a pronounced dry season and rely on their succulent stems or tuberous roots to carry them through.
Notable species
Some of the better-known plants long grown under this name include:
- Monadenium ritchiei — a popular, cylindrical, tubercled species making short fingers of green flesh, often with pink bracts.
- Monadenium guentheri — a robust, branching, columnar grower widely passed around among collectors.
- Monadenium rubellum — a caudiciform species with a swollen rootstock and soft, seasonal shoots.
- Monadenium ellenbeckii — a slender, near-leafless, upright grower valued as an easy houseplant.
- Monadenium magnificum — a taller, leafier species with showy bracts.
Each of these also appears in the trade and modern references under its Euphorbia combination.
Cultivation
These are among the more forgiving succulent spurges and make excellent collection plants. Grow them in a very free-draining, mostly mineral mix, in bright light — good light keeps the stems compact and well-coloured, while too little draws them out. Water regularly through the warm growing season once the mix has dried, then taper off sharply as temperatures fall: most are winter-dormant and should be kept dry and frost-free through the cold months. Caudex- and tuber-forming kinds are especially unforgiving of winter wet at the root.
Keep them warm; few tolerate frost, and they are happiest treated as tender plants or grown under cover in cool climates. See Watering and Repotting for general technique.
A word of caution: like all Euphorbia, these plants bleed a milky latex that is an irritant to skin and especially to the eyes. Handle cuttings carefully, wash off any sap, and keep the latex away from your face. See Pests and diseases for the usual mealybug and rot troubles.
Propagation
Most branching and clumping kinds root easily from stem cuttings taken in the growing season: cut a shoot, rinse or blot the bleeding latex, let the end callus for several days, then set it in a gritty mix. Clumping species can also be divided at repotting time, and many can be raised from seed where it is available. Caudiciform species are usually grown from seed to develop a good rootstock.
See also
- Euphorbia — the genus these plants now belong to
- Euphorbiaceae — the spurge family
- Soil and potting mix · Watering · Repotting
- Propagation - cuttings · Propagation - seed · Pests and diseases