I have walked by several homes with beautiful coleus in beds around trees and along the fronts of houses. It is quite striking and really brings attention to the landscaping. Plus, it does not require full sun which makes it perfect for shady areas. I have even grown some myself, and I do not have a green thumb. However, I don’t have any right now. Having endured 14-15 months of a pandemic so far can be stressful for anyone. But seeing those coleus bursting with color really brightens my day. Let’s learn more about it.
Coleus is a genus of annual or perennial herbs or shrubs — sometimes succulent, sometimes with a fleshy or tuberous rootstock — found in the Old World tropics and subtropics. The relationship among the genera Coleus, Solenostemon and Plectranthus has been confused. Coleus and Solenostemon were sunk into Plectranthus, but recent phylogenetic analysis found Plectranthus to be paraphyletic with respect to other related genera in the subtribe Plectranthinae. The most recent taxonomic treatment of the genus resurrected Coleus, and 212 names were changed from combinations in Plectranthus, Pycnostachys and Anisochilus. Equilabium was segregated from Plectranthus, after phylogenetic studies supported its recognition as a phylogenetically distinct genus.
Coleus are cultivated as ornamental plants, particularly Coleus scutellarioides — syns. Coleus blumei, Plectranthus scutellarioides — which is popular as a garden plant for its brightly colored foliage. This plant prefers bright, but indirect sunlight. If direct sunlight touches the plant's leaves, the colors become less brightly colored. Outside this plant needs total shade or only the most mild morning sunlight.
Other species that produce root tubers are cultivated for food, including Coleus esculentus, Coleus rotundifolius and Coleus maculosus subsp. edulis.
The genus Coleus was first described by Portuguese Jesuit missionary and botanist João de Loureiro in 1790. Using morphological characters as a guide, it was distinguished from Plectranthus — first described by Charles L'Héritier in 1788 — by having its four stamens fused together rather than free to the base. In 1962, J.K. Morton noted that fused stamens were more widespread than previously thought, and accordingly merged Coleus into Plectranthus, while maintaining Solenostemon and some other genera as distinct. Most sources followed Morton in submerging Coleus; some kept Solenostemon distinct, although others submerged it into Plectranthus along with Coleus.
A preliminary study of the tribe Ocimeae in 2004 showed that the subtribe Plectranthinae was monophyletic, with two main clades: one containing the type species of Coleus and including Solenostemon, the other containing the type species of Plectranthus along with some other genera, so that Plectranthus when broadly defined was not monophyletic. A more detailed study in 2018 reached similar conclusions, and suggested that Coleus — including Solenostemon — should be recognized again, Plectranthus more narrowly defined, and a new genus, Equilabium erected for a clade of former Plectranthus species mainly from tropical Africa. The many new binomial combinations needed to implement this approach were provided in 2019.
Selected species
Coleus australis, little spurflower or cockspur flower
Coleus australis — synonyms Plectranthus australis and Plectranthus parviflorus — known as little spurflower[2] or cockspur flower is a shrub occurring in Hawaii, Polynesia and Australia. Non aromatic, between 10 and 70 cm high. The habitat is shady moist areas, including eucalyptus forest and rainforest. A widespread species, in rocky areas and beside streams. Attractive blue and white flowers may occur throughout the year.
Coleus barbatus
Coleus barbatus — also known by the synonyms Plectranthus barbatus and incorrectly Coleus forskalaei and other spellings of this epithet — is a tropical perennial plant related to the typical coleus species. It produces forskolin, an extract useful for pharmaceutical preparations and research in cell biology.
The Brazilian name is boldo brasileiro or boldo gaúcho as opposed to the Chilean true boldo, boldo-da-terra, boldo-de-jardim or tapete-de-Oxalá — Oxalá's carpet, because of its velvety texture.
Herbal teas made from Coleus barbatus contain rosmarinic acid and also flavonoid glucuronides and diterpenoids. The chemical constituents of Plectranthus barbatus showed activities in vitro, such as acetylcholinesterase inhibition.
In Ayurvedic traditional medicine, Coleus has been used to treat heart diseases, spasmodic pain, painful urination and convulsions.
Coleus caninus — synonym Plectranthus caninus — is a herb from the mint family Lamiaceae, native to southern and eastern Africa from Angola to Sudan and to India and Myanmar.
A plant sold under the name "Coleus canina" or "scaredy cat plant" is supposed to scare off cats and dogs. An attempt to register "Coleus canina" to receive plant variety protection failed as it was considered to be only a clone of Coleus comosus, synonym Plectranthus ornatus.
Coleus comosus
Coleus comosus — synonym Plectranthus ornatus — is a flowering plant from the mint family Lamiaceae, native to eastern Africa i.e., Eritrea, Ethiopia, Kenya, Tanzania and Uganda.
Coleus esculentus, kaffir potato or Livingstone potato
Coleus esculentus — synonym Plectranthus esculentus, also known as the kaffir potato or Livingstone potato — is a species of plant in the dicot family Lamiaceae. It is indigenous to Africa, where it is grown for its edible tubers. It is more difficult to cultivate than Coleus rotundifolius, but able to give greater yields. Although the crop is similar to a potato, it is from the mint family, but it is still quite nutritious and useful. This crop can benefit many subsistence farmers since it is native, easy to grow, enjoying growing popularity in the market and quite nutritious.
The species is a perennial dicot herb and a member of the mint family. It can grow to be as tall as 2 meters. Some of the branches on the base bend down and grow into the ground that then can form oblong tubers, which are the fleshy underground stems. These tubers are edible and nutritious, often eaten as a substitute for potato or sweet potato. Although they are rarely seen because the vegetative reproduction is predominant, the plant also has yellow flowers. These flowers are two-lipped, and are on the short and crowded branches. While the plant is in flower, the stems are leafless. Coleus esculentus has fleshy leaves on angular stems. These leaves have brown gland-dots underneath and toothed edges. The tubers of this plant are quite important since that is the part of the crop that is used for sale and farmer exchange.
The tubers are the most useful part of Coleus esculentus for humans. These tubers are nutritious and easy to grow and are becoming easier to sell. The tubers can remain viable underground even when the plant is not able to produce leaves. Coleus esculentus can adapt well to various environmental conditions but does best in local environmental conditions where there has been a history of cultivation, such as Southern Africa. People who are trained in a community are able to manage the production of C. esculentus with little additional help.
The tubers have been planted in small plots of 10 by 10 meters. In these small plots they were planted between young eucalyptus trees, using a mixed cropping system that had vegetables like amaranthus and cucurbits. They have also been intercropped with maize but that proved to be unsuccessful. Yields were lower when intercropped with maize.
Some cultivated tubers can weigh up to 1.8 kg. Yields of 2-6 tons per hectare have been reported. Yields of 70 tons per hectare were documented when the leaves could be harvested. They were harvested on a two-week interval and over a period of six weeks. Yields will depend on weather conditions and the various types of soil.
In 2001-2002 farmers were able to sell 250 g of this crop for up to 5 rand or $1, which is higher than the price of an Irish potato. Communities can also sell the cooked leaves for 7 rand or $1.30. There is a cash demand for Coleus esculentus, but it is typically exchanged between neighbors and friends.
Women have high knowledge of this crop including nutritious value and cultivation practices because it is indigenous. This is an advantage for farmers since they have the initial knowledge to grow this crop and the potential to be successful in the first season of harvest.
Coleus graveolens
Coleus graveolens — synonym Plectranthus graveolens — is a shrub in the family Lamiaceae. It is native to New South Wales and Queensland in Australia.
Coleus neochilus, lobster bush, fly bush or mosquito bush
Coleus neochilus — synonym Plectranthus neochilus — which is colloquially known as lobster bush, fly bush or mosquito bush, is a perennial ground cover with highly fragrant, partially scalloped, ovate leaves and purple blue inflorescent spikes.
The succulent, grey-green leaves present with small hairs on the tops, and a grey-green color. The plant itself remains a ground cover for the duration of its life, forming massive bushes rather quickly. The aroma of the plant has been said to resemble cannabis. They bloom twice a year, in late summer and in late winter.
The plant is found in dry brush lands, open and sometimes rocky woodland, from the Western Cape, Eastern Cape, KwaZulu-Natal, Mpumalanga to Limpopo in South Africa, as well as in Zimbabwe, Zambia and Namibia.
Lobster bushes can tolerate wide temperature ranges, dry conditions and almost any soil, but prefer a well-drained sandy loam in full sun or partial shade. Hard pruning is suggested after flowering. Stems root very readily, and the plant extends, where it forms a tidy cluster. Often planted in the landscape of difficult areas, the plant may become a little stressed in very dry conditions but would revive when it receives some water. They can easily be propagated from softwood cuttings and would multiply in the garden. They are rarely affected by pests.
It is said that this plant can repel snakes, mosquitoes, flies and most garden pests as a result of its fragrant nature. This makes Coleus neochilus an ideal companion plant for vegetable gardens. Furthermore, reports point out that these plants can be used efficaciously as an air purifier.
The dried herb, known as "boldo" or "boldo-gambá," is employed for treating hepatic insufficiency and dyspepsia in folk medicine. Tea made by steeping fresh leaves is similar to mint tea.
Coleus scutellarioides
Coleus scutellarioides, commonly known as coleus, is a species of flowering plant in the family Lamiaceae (the mint or deadnettle family), native to southeast Asia through to Australia. Typically growing to 24–30 inches tall and wide, it is a bushy, woody-based evergreen perennial, widely grown for the highly decorative variegated leaves found in cultivated varieties. Another common name is painted nettle, reflecting its relationship to deadnettles, which are in the same family. True nettles and their close kin are in the family Urticaceae. The synonyms Coleus blumei, Plectranthus scutellarioides and Solenostemon scutellarioides are also widely used for this species.
The leaves of the wild species may be somewhat variegated, but this has been developed to an extreme degree in cultivated varieties, whose leaves may include one or more shades of green, white, cream, yellow, pink, red, maroon and dark purple. Green coloration is due to the amount of chlorophyll present in the chloroplasts in the leaves. Red, purple, pink and orange colors are due to anthocyanins — water-soluble, flavonoid biosynthetic pigments — found in the foliage in addition to chlorophyll. The increase in anthocyanin production is accompanied by a decrease in chlorophyll production. The production of anthocyanins and chlorophyll is affected by light levels; the more light is present, the more anthocyanins are produced, with an inverse relationship to the production of chlorophyll. Anthocyanins are created inside the cell and facilitate photosynthesis in leaves that are exposed to very intense or prolonged sunlight by providing protection from damage caused by ultraviolet light. Some coleus cultivars overproduce anthocyanins and underproduce chlorophyll to the extent that optimal growth is prevented.
Coleus scutellarioides is native from southeast Asia through to Australia — the Bismarck Archipelago, Borneo, Cambodia, Southeast China, Java, Laos, the Lesser Sunda Islands, Peninsular Malaysia, Maluku, Myanmar, Nansei-shoto, New Guinea, Northern Territory, Philippines, Queensland, the Solomon Islands, Sulawesi, Sumatra, Taiwan, Thailand, Vietnam and Western Australia. It is cultivated worldwide and may be naturalized in other tropical regions. In its native habitat, it is found at elevations of 330–5,250 feet, where it flowers and fruits throughout the year. It is winter hardy to USDA Zones 10–11.
The species was first introduced into Europe from Java in 1851 by a Dutch horticulturalist. At this time, there were few leaf colors and shapes. A wider variety was available by 1877, when the American William Bull offered seeds at 43 cents each. However, by selecting for seed production, early flowering was inadvertently favored, and leaf color also declined in intensity. Coleus breeding revived in the early 1940s, and by the 1980s, the availability of an improved range of cultivars led to coleus becoming the tenth most important bedding crop in the U.S. More recently, vegetative propagation has enabled cultivars with novel leaf colors and shapes to be offered for sale. Plants with trailing as well as upright habits are now available.
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