Close-up views:

The young plants:

The overall appearance of this plant resembles that of the Indian Borage (Plectranthus amboinicus). One feature that separates them is the characteristic of the stem. Plectranthus monostachyus has a 4-angled stem while that of Indian Borage is round. Some matured plants seemed to have nodules among its roots. Additionally, it seemed that Indian Borage rarely bears flowers while Plectranthus monostachyus bears flowers frequently.

The synonym Solenostemon monostachyus is used more often when referring to this herb. The transferred of Solenostemon monostachyus to Plectranthus was described in a publication by Kew in 2001 [1].

Based on the numerous articles published over the years, mostly from Africa on its medicinal potential [2-7], it is quite certain that this plant originated from that region. The first time that I came across this plant in Singapore was in 2007 at Sungei Buloh Wetland Reserve, around the outdoor classroom area. A large population could be seen thriving on a deserted plot that was used to grow some other herbs in the past. Subsequently, I saw more of them in a number of open areas. The plant was not listed in the Singapore flora checklist published in 2009. Interestingly, Indian Borage (Plectranthus amboinicus) was also not listed in the plant checklist although it is a common cultivated herb here. Finally, the official documentation came along on 15 May 2015, in the form of an article published in the Nature in Singapore online journal [8].

References:

[1] Pollard BJ, Paton A. A New Rheophytic Species of Plectranthus L'Her. (Labiatae) from the Gulf of Guinea. Kew Bulletin 2001;56(4):975-982.

[2] Afolabi IS, Osikoya IO, Fajimi OD, Usoro PI, Ogunleye DO, Bisi-Adeniyi T, Adeyemi AO, Adekeye BT. Solenostemon monostachyus, Ipomoea involucrata and Carica papaya seed oil versus Glutathione, or Vernonia amygdalina: methanolic extracts of novel plants for the management of sickle cell anemia disease. BMC Complement Altern Med 2012;12:262. | Read article |

[3] Okoko T, Ere D. Antioxidant activities of Solenostemon monostachyus leaf extract using in vitro methods. Sci Res Assays 2012;7:621. | Read article |

[4] Fidele KZ, Andre KB, Yao DJ, Michel OA. Action of hydroethanolic leaves extract of Solenostemon monostachyus (lamiaceae) on cardiovascular system of mammalians: blood pressure lowering effects. Int J Pharm Bio Sci 2012;2(3):310-320. | Read article |

[5] Jacques DY, Fidele K, Michel OA. Acute toxicity and antioxidant activity of hydroethanolic extract of Solenostemon monostachyus P. Beauv. leaves. J Compl Integ Med 2010;7(1).

[6] Onu UO. Some pharmacological properties Solenostemon monostachyus. J Herbs Spices Med Plants 1996;4(2):3-7.

[7] Mve-Mba CE, Menut C, Lamaty G, Zollo PHA, Tchoumbougnang F, Bessiere JM. Aromatic plants of tropical central Africa. Part XIX. Volatile components from leaves of two lamiaceae from Cameroon: Leucas deflexa hook and Solenostemon monostachyus (P.Beauv.) Briq. Flavour Fragrance J 1994;9(6):315-317.

[8] Chung YS, Teo S, Chong KY, Kurukulasuriya BR, Tan HTW. Weed risk assessments of the exotic species of Plectranthus L'Her. (Lamiaceae) in Singapore. Nature in Singapore 2015;8:1-13. | Read article |

Online Resources:

| The Virtual Botanic Garden | West African Plants | Tropicos |