Plectranthus L'Hér.

Lamiaceae (Labiatae), A.J. Paton, G. Bramley, O. Ryding, R.M. Polhill, Y.B. Harvey, M. Iwarsson, F. Willis, P.B. Phillipson, K. Balkwill, C.W. Lukhoba, D.F. Otieno, & R.M. Harley. Flora of Tropical East Africa. 2009

Morphology General Habit

Perennial or annual, sometimes succulent, subshrubs or herbs or geoxylic herbs, usually aromatic

Morphology Stem

Stems usually branched

Morphology Leaves

Leaves simple, rarely bipinnate, opposite, rarely ternate, very rarely scattered

Morphology Reproductive morphology Inflorescences

Inflorescence thyrsoid, condensed or lax, with cymes sessile or pedunculate, bracteate, very rarely braceolate, 1–many-flowered; bracts caducous or persistent; pedicel very rarely jointed with distal part falling with calyx

Morphology Reproductive morphology Flowers Calyx

Calyx funnel-shaped or shortly tubular, with the pedicel attaching symmetrically at the centre of the calyx base, or asymmetrically behind the posterior lip, straight or slightly or strongly curved, strongly 2-lipped or actinomorphic, 5lobed (1/4 (1 posterior, 4 anterior), rarely 3/2 or actinomorphic); lobes equal or unequal; posterior lip lanceolate to obovate, sometimes decurrent; lateral lobes rounded to lanceolate; anterior lobes lanceolate to subulate at apex, sometimes fused for part of their length, rarely with a deep split between them; throat open, truncate or oblique, glabrous or bearded, very rarely circumscissile at base

Morphology Reproductive morphology Flowers Corolla

Corolla white, blue, purple or yellow, strongly 2-lipped, 5-lobed (4/1); posterior lip long or short, ascending, reflexed or truncate, 4-lobed, median lobes usually exceeding lateral; anterior lip horizontal or sometimes finally deflexed, cucullate or concave; corolla-tube narrow, straight, variously curved or sigmoid, parallel-sided, more rarely gibbous or spurred at base, dilating distally and parallel-sided or narrowing towards throat, very rarely annulate within

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 4, fused or free and adjacent at base, fused to corolla at corolla throat at the base of the anterior lip, held within anterior lip or exserted; anthers usually ± orbicular, dorsifixed, synthecous, sometimes ellipsoid, but rarely with outer edges of locules fused in lower half to form a pouch which opens apically

Morphology Reproductive morphology Flowers Disc

Disk 4-lobed with anterior lobe larger, sometimes exceeding ovaries

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary glabrous, very rarely pubescent at apex, deeply 4-lobed; style bifid with lobes spreading, subulate or linear or rarely entire

Morphology Reproductive morphology Fruits

Nutlets ovoid, slightly flattened or not, glabrous, rarely pubescent, mucilaginous or not 2 n = 24–48(–84)

Note

ON CONSERVATION: Information from herbarium specimens has been used to calculate preliminary conservation assessments for Plectranthus species endemic to the F.T.E.A. and Flora Zambesiaca areas, as outlined in Willis, Moat & Paton (2003). In these cases the following abbreviations have been used. EOO: extent of occurrence; AOO: area of occupancy (see also www.iucnredlist.org/info/categories_criteria). Subpopulations were calculated using adjacent cells (Schatz et al., 2000) and by Rapoport distances using a barrier distance twice the average line length from the minimum spanning tree (MST) and buffer distance is the average line length of MST (Rapoport, 1982). Within the ‘Coleus’ clade there are several groups of species: 38–39 have an entire style and have been recognized as Holostylon; 83–91 have fused anterior calyx lobes and have been recognized as Solenostemon; 93–100 have a dense ring of hairs in the calyx throat (subgen. Calceolanthus Codd). However within both the major clades, and, to a small extent, between the main clades themselves, there are species which do not fall into readily recognizable, mutually exclusive groups. Within both clades there are some groups of species which can be recognized. In the ‘Plectranthus’ clade species 2 and 3 have an oblique calyx throat with the lateral lobes of the calyx closer to the median lobes of the anterior (lower) lip than to the posterior (upper) lip and the corolla tube is saccate at the base; other species having a truncate calyx throat and usually non-saccate, usually sigmoid corolla tube. Species 26–32 have a rootstock and produce stems annually. The ‘Plectranthus’ clade of Paton et al. (2004) is represented by species nos 1–33. These species have the anterior and posterior lips of the corolla ± equal in length, a symmetrical calyx base with the pedicel attaching at the midline of the calyx, free stamens and ovoid nutlets. The ‘Coleus’ clade is represented by species 35–104. In this group the posterior corolla lip is usually shorter than the anterior, the calyx is usually asymmetric at the base with the pedicel behind the posterior lip of the calyx; the stamens are free or fused and the nutlets are often flattened. ON GROUPINGS OF PLECTRANTHUS: A formal classification is not adopted here. A phylogenetic overview of the genus is presented in Paton et al. (2004) and Lukhoba et al. (2006) and provides a working informal grouping of species. These treatments are not congruent with previous morphological classifications, such as that by Codd in Bothalia 11: 371–442 (1975). Further work is needed before proposing a formal classification. The key to Plectranthus by Codd in Fl. Southern Africa provides a good basis for identifying the cultivated Plectranthus of southern tropical Africa. P. scutellarioides (L.) R.Br. ( Coleus blumei Benth.) from tropical Asia is similar to P. dupuisii below and is widely cultivated for its brightly coloured and variegated, sometimes incised leaves.

J. R. Timberlake, E. S. Martins (2013). Flora Zambesiaca, Vol 8: part 8. Royal Botanic Gardens, Kew

Morphology General Habit

Perennial or annual, sometimes succulent, subshrubs or herbs or geoxylic herbs; usually aromatic- Stems usually branched

Morphology Leaves

Leaves simple, rarely bipinnate, opposite, rarely ternate, very rarely scattered

Morphology Reproductive morphology Inflorescences

Inflorescence thyrsoid, condensed or lax, with cymes sessile or pedunculate, bracteate, very rarely braceolate, 1 to many-flowered; bract caducous or persistent; pedicel very rarely jointed, distal part falling with calyx

Morphology Reproductive morphology Flowers Calyx

Calyx funnel-shaped or shortly tubular, with pedicel attaching symmetrically at centre of calyx base or asymmetrically behind posterior lip, straight or slightly or strongly curved, strongly 2-lipped or actinomorphic, 5-lobed (1/4 (1 posterior, 4 anterior), rarely 3/2 or actinomorphic); lobes equal or unequal; posterior lip lanceolate to obovate, sometimes decurrent; lateral lobes rounded to lanceolate; anterior lobes lanceolate to subulate at apex, sometimes fused for part of their length, rarely with a deep split between them; throat open, truncate or oblique, glabrous or bearded, very rarely circumscissile at base

Morphology Reproductive morphology Flowers Corolla

Corolla white, blue, purple or yellow, strongly 2-lipped, 5-lobed (4/1); posterior lip long or short, ascending, reflexed or truncate, 4-lobed, median lobes usually exceeding lateral; anterior lip horizontal or sometimes finally deflexed, cucullate or concave; corolla-tube narrow, straight, variously curved or sigmoid, parallel-sided, more rarely gibbous or spurred at base, dilating distally and parallel-sided or narrowing towards throat, very rarely annulate within

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 4, fused or free and adjacent at base, fused to corolla at corolla throat at base of anterior lip, held within anterior lip or exserted; anther usually ± orbicular, dorsifixed, synthecous, sometimes ellipsoid, rarely with outer edges of locules fused in lower half to form a pouch which opens apically

Disc

Disk 4-lobed with anterior lobe larger, sometimes exceeding ovaries

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary glabrous, very rarely pubescent at apex, deeply 4-lobed; style bifid with lobes spreading, subulate or linear or rarely entire

Morphology Reproductive morphology Fruits

Nutlets ovoid, slightly flattened or not, glabrous, rarely pubescent, mucilaginous or not 2n = 24–48(84).

Distribution

About 300 species in the Old World tropics.

Recognition

The ‘Plectranthus’ clade of Paton et al. (2004) is represented by species 1–31. These species have ± equal corolla lobes, a symmetrical calyx base with the pedicel attaching at the mid-line of the calyx, free stamens and ovoid nutlets. The ‘Coleus’ clade is represented by species 32–91. In this group the posterior corolla lobe is usually shorter than the anterior, the calyx is usually asymmetric at the base with the pedicel attaching behind the posterior lip of the calyx, the stamens are free or fused and the nutlets are often flattened. Within both clades there are some groups of species which can be recognized. In the ‘Plectranthus’ clade species 1 to 9 have an oblique calyx throat with the lateral lobes of the calyx closer to the median lobes of the anterior (lower) lip than to the posterior (upper) lip and the corolla tube is saccate at the base; other species having a truncate calyx throat and usually non-saccate, usually sigmoid corolla tube. Species 24–31 have a rootstock and produce stems annually. Within the ‘Coleus’ clade there are several groups of species: 34–36 have an entire style and have been recognized as Holostylon, although P. bifidus (37) is intermediate between this group and other members of the ‘Coleus’ clade; 73–79 have fused anterior calyx lobes and have been recognized as Solenostemon; 80–84 have a dense ring of hairs in the calyx throat (subgenus Calceolanthus Codd). However, within both the major clades, and to a small extent between major clades, there are species which do not fall into readily recognizable, mutually exclusive groups. Many Plectranthus species are used widely in traditional medicine; these and other uses are reviewed in Lukhoba, Simmonds & Paton (J. Ethnopharm. 103: 1–24, 2006). The tubers of Plectranthus esculentus, P. rotundifolius, and P. punctatus subsp. edulis are eaten in Africa, though there is only limited use within the Flora area. P. amboinicus, P. barbatus var. grandis, P. hadiensis and P. neochilus are the most commonly cultivated native or naturalized species, with P. lanuginosus also being naturalized in E Zimbabwe. P. ecklonii Benth., P. fruticosus L’Hér., P. madagascariensis (Pers.) Benth. cultivars ‘Variegated Mintleaf’, ‘Marginatus’ and ‘Variegatus’ (all variegated forms), P. saccatus Benth., P. strigosus Benth., P. oertendahlii T.C.E. Fr. and P. verticillatus (L.f.) Druce are commonly grown in horticulture. This is unlikely to be a complete list. All these horticultural species originate in South Africa; the South African horticultural trade has been expanding the number of South African species which are available.

Conservation

Information from herbarium specimens has been used to produce preliminary conservation assessments for species endemic to the F.T.E.A. and Flora Zambesiaca areas (see Willis, Moat & Paton, Biodiv. Cons. 12: 1537–1552, 2003). The following abbreviations are used: EOO = Extent of Occurrence; AOO = Area of Occupancy (see www.iucnredlist.org/info/categories_criteria) Subpopulations were calculated using adjacent cells (Shatz et al. in Lourenço & Goodman, Diversité et Endemisme à Madagascar. Paris, 2000) and by Rapoport distances using a barrier distance twice the average line length from the minimum spanning tree (MST) and buffer distance is the average line length of MST (Rapoport, Areography: Geographical Strategies of Species. Pergamon, New York, 1982).