Cotyledon
Cotyledon is a small genus of shrubby succulents in the stonecrop family Crassulaceae, native chiefly to southern Africa. Its members are woody-based perennials with pairs of thick, opposite leaves — often felted, powdery or edged in red — and slender flower stalks that carry nodding, tubular bell-shaped blooms. The best-known member, the pig's ear, has made the genus a familiar sight in dry gardens and collections worldwide.
Description
Cotyledon are evergreen shrublets and small shrubs, usually forming a branching woody base from which pairs of fleshy leaves arise in opposite, alternating ranks (decussate). The leaves are the genus's signature feature: thick and rounded, frequently coated in a chalky white farina or a fine felt of short hairs, and often outlined with a fine red or maroon margin. Shape ranges from the broad, flat, paddle-like leaves of C. orbiculata to the plump, toothed, paw-like leaves of C. tomentosa.
The flowers are held well above the foliage on tall, branching stalks and hang downward as clusters of tubular, bell-shaped blooms in shades of orange, red, yellow and salmon. This pendent, tubular flower — adapted for bird and insect pollination — is a reliable way to tell Cotyledon apart from its close relatives Kalanchoe and Tylecodon. Unlike the deciduous, tuberous-stemmed Tylecodon (which was split off from Cotyledon), true Cotyledon keep their leaves year-round and retain them on the same points of the stem.
A note of caution: like many Crassulaceae, Cotyledon species contain bufadienolide compounds and are toxic if eaten, to livestock, pets and people. In their homeland heavy grazing of some species causes the stock disease known as "krimpsiekte." They are best kept out of reach of animals and children.
Distribution
The genus is centred on southern Africa — South Africa, Namibia, Botswana and neighbouring countries — with a few species reaching into the drier parts of the Arabian Peninsula and East Africa. Plants typically grow in arid and semi-arid habitats: rocky outcrops, well-drained slopes and open scrub, where their waxy or felted leaf coatings help reflect sun and reduce water loss.
Notable species
- Cotyledon orbiculata — the pig's ear, by far the most widely grown species, with broad grey, white-powdered leaves often edged in red; extremely variable, with many named leaf forms.
- Cotyledon tomentosa — the bear's paw, a smaller, densely fuzzy species whose plump leaves are tipped with several tooth-like points, resembling a paw. A popular variegated form exists.
- Cotyledon woodii — a compact, freely branching shrublet with grey-green leaves, valued as an easy, floriferous plant.
- Cotyledon papillaris — a low, spreading species with small glossy leaves and bright red-orange flowers.
Cultivation
Cotyledon are among the more forgiving succulents and make good subjects for a bright windowsill, a frost-free greenhouse or a dry garden in mild climates. Grow them in a gritty, free-draining mix and give them as much bright light as possible — good light keeps growth compact and preserves the leaf colour and powdery coating. In too little light plants stretch and lose their form.
Water thoroughly when the soil has dried out, then allow it to dry again before watering next; err on the dry side, as the thick leaves store plenty of reserves and rot is the main risk (see Watering). Reduce water in winter, when most species rest. A little dilute feed in the growing season supports flowering. Take care when handling the powder-coated species — the farina rubs off easily where fingers touch and does not grow back until the leaf is shed. Most tolerate light frost at best, so protect them from freezing; see Repotting for general technique.
Watch for the usual succulent pests — mealybugs tucked into leaf axils, and root mealybugs below the soil line — and treat promptly.
Hobby and cultivar notes
Cotyledon orbiculata in particular has given rise to a range of selected leaf forms, differing in leaf width, colour and the redness of the margin; these are usually maintained by cuttings to keep them true. The variegated form of C. tomentosa (bear's paw) is a sought-after collector's plant but is slower and softer than the plain green form, and needs bright light and careful watering to thrive. Gardeners should be aware that some plants once sold as Cotyledon — the deciduous, caudex-forming species — now belong to the segregate genus Tylecodon and are cared for differently, with a summer rest rather than a winter one.
Propagation
Cotyledon are easy to increase. Stem cuttings root readily: take a healthy shoot, let the cut end callus for a few days, then set it in a dry, gritty mix and water sparingly until roots form. Unlike many other Crassulaceae, Cotyledon are unreliable from single leaves, so stem cuttings are the usual vegetative method. Species come true from seed sown on a fine mineral surface kept warm and lightly moist, but named leaf forms are best kept going vegetatively.
See also
- Crassulaceae — the stonecrop family
- Cotyledon orbiculata · Cotyledon tomentosa — the most-grown species
- Kalanchoe · Tylecodon — closely related genera
- Soil and potting mix · Watering · Propagation - cuttings · Pests and diseases