Origin and Habitat: Plectranthus ernstiiSN|35391]]SN|35391]] is known from less than 10 locations from Oribi Gorge to Mkambati, in the Eastern Cape and KwaZulu-Natal, South Africa.
Habitat and Ecology: Scarp Forest, in humus-rich pockets of soil in rock crevices on south-facing cliffs. The soil is mineral poor, and well drained. In these areas rain falls in summer and averages between 800-1500 mm per annum. Plectranthus ernstiiSN|35391]]SN|35391]] grows on sheer rocky ledges out of reach of most predators. The succulent stems, which store water and nutrients, and a very compact growth habit, enabling the plants to cope with a dry cliff-face habitat. Associated succulents include Crassula perforataSN|21901]]SN|21901]], Gasteria croucheriSN|17219]]SN|17219]] and Aeollanthus parvifolius. The aromatic leaves possibly discourage insect predators. The flowers are pollinated by insects. P. ernstii is potentially threatened by invading alien plants.

• Plectranthus ernstii Codd

Description: The bonsai mint (Plectranthus emstii) is a erect to decumbent, compact, perennial semi-succulent herb up to 25 cm tall, branching from the base. It has felted, pleasantly scented, semis-ucculent leaves. It eventually produces a very swollen basal caudex, developing slowly with age. With some pruning, these plants end up looking like a short bonsai shrub, and the swollen, almost potato-like stem bases distinguish P. ernstii from all other species. It also readily produces its stalks of flat-petalled, pale bluish mauve flowers.
Derivation of specific name: The specific epithet "ernstii" is named after the horticulturist Ernst van Jaarsveld (1953- ).
Stems: Thickened at the base, 20 to 50 in diameter, greyish and articulated becoming brown and potato-like with age. The branches with segments and distinct nodes or joints are brittle and easily broken.
Leaves: Petiolate and aromatic. The leaf blade is semi-succulent, ovate to broadly ovate, to somewhat triangular,12-30 mm long, 10-25 mm broad, sparsely covered in short fine soft hairs, under-surface often covered in fine hairs and pale to reddish brown gland-dots.. The apex is obtuse and the base is truncate. The margin with few, with 3-5 pairs of fairly distinct rounded teeth. The petiole is 6-13 mm long. The leaves turn-rose pink during autumn.
Inflorescence Simple, 3-12 cm long and persistent. The flowers are arranged in sessile, 1-3-flowered cymes, forming whorls (verticils) of 2-6 flowers, 10-20 mm apart, with the flowers at the tip opening first.
Flowers: Small, sessile, two-lipped, pale bluish mauve to whitish with darker markings. Calyx 3 mm in diameter while in flower, enlarging to 5-6 mm long in fruiting stage, glandular-hispidulous. Corolla pale bluish mauve to whitish. Corolla tube 4-8 mm long, expanding abruptly and forming a pouch-like base 4-5 mm deep, narrowing gradually to 2 mm deep at the throat. Upper lip 4-5 mm long, lower lip concave, 3-4 mm long. Stamens free, of two lengths, upper pair 1,5 mm long, lower pair 3 mm long. The flowers are rather like those of Plectranthus praetermissus but are smaller
Blooming season: . Flowering time is late spring to autumn (October to May) with a peak in autumn (April), and flowers can appear sporadically throughout the year.
Fruit: 2 mm long, light brown nutlet, up to four per flower, attached inside the calyx.

Bibliography: Major references  and  further lectures 
1) Robert Allen Dyer, L. E. W. Codd, Hedley Brian Rycroft, “Flora of southern Africa”, Volume 28, Parte 4, Govt. Printer, 1963
2) J.P. Roux, “Flora of South Africa”, 2003
3) Philippe De Vosjoli, “The Art Of Keeping Snakes” i5 Publishing, 7 ago 2012
4) Gideon Smith, “Guide to Succulents of Southern Africa” Penguin Random House South Africa, 5 November 2011
5) Domitilla Raimondo, “Red list of South African plants 2009”, South African National Biodiversity Institute, 2009
6) Scott-Shaw, C.R. “Rare and threatened plants of KwaZulu-Natal and neighbouring regions”. KwaZulu-Natal Nature Conservation Service, Pietermaritzburg. 1999
7) Scott-Shaw, C.R., van Jaarsveld, E.J. & Victor, J.E. 2005. Plectranthus ernstii Codd. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2018/09/30
8) Codd, L.E. Plectranthus ernstii. “The Flowering Plants of Africa” 47: 1855, 1982
9) Codd, L.E., Lamiaceae in “Flora of South Africa”, ed. O.A. Leistner, Vol. 28 Part 4. Botanical Research Institute, Pretoria. 1985
10) Glen, H.F. & Germishuizen, G. (compilers), “Botanical Exploration of Southern Africa”, edition 2. Strelitzia 26. South African National Biodiversity Institute, Pretoria. 2010
11) Hutchings, A. Haxton Scott A., Lewis G., Cunningham Balfour A., “Zulu Medicinal Plants An Inventory”. University of Natal Press, Private Bag X01 Scottsville 3209, 1996.
12) Pooley, E., “A Field Guide to Wild Flowers Kwazulu - Natal and the Eastern Regions”. Natal Flora Publications Trust, Durban 1998.
13) Raimondo, D., Von Staden, L., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds) 2009. “Red List of South African plants 2009”. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
14) Van Jaarsveld, E. 1987. “The Plectranthus Handbook”. National Botanic Gardens, Cape Town.
15) Van Jaarsveld, E. 2006. “The Southern African Plectranthus and the art of turning shade to glade”. Fernwood Press, Simon's Town, South Africa.
16) Van Wyk, B. & Gericke, N. 2007. “People's Plants a Guide to Useful Plants of Southern Africa”. Briza Publications, Pretoria.
17) Cactus World: The Journal of the British Cactus & Succulent Society, Volume 25, British Cactus & Succulent Society, 2007
18) Kyle Smith & Alice Notten, Plectranthus ernstii Codd, web: http://pza.sanbi.org/plectranthus-ernstii

Cultivation and Propagation: P ernstii is a slow growing species that adapts to a variety of conditions in tropical and warm climates as long as the substrate has good drainage. It should also do well in retaining walls and on steep rocky slopes. It resembles a bonsai, and is ideal for pot plants and rockeries.
Soil: Well-drained, but humus enriched.
Exposure: Full sun, semi-shade or bright shade.
Watering: It prefers to be watered all year round expecially in summer, provided that it is not subjected to frost, and care should be taken not to over water as this will cause the roots to rot.
Maintenance: Prunening P. ernstii frequently to maintain a neat 'bonsai' shape is an essential practice which improves the quality of plants and flowering.
Propagation: Seed or by cuttings. Cuttings produce roots fairly quickly.