**1. Introduction**

Essential oils (EOs) are aromatic oily liquids composed of a complex mixture of volatile compounds and are produced by aromatic plants as secondary metabolites. The volatile constituents of EOs have been important materials for preventing and treating human diseases since the early days [1]. Although mainly used for their agreeable scents, EOs present themselves as excellent candidates to meet the current beauty industry's demands for two principal reasons. Firstly, research backs up their efficacy as valuable cosmeceuticals. They have been shown to exhibit properties of antimicrobials [2,3], antioxidant agents [4,5], antityrosinase agents [6–8], sunscreens [9,10], natural preservatives [11], natural sources of fragrance [12], as well as inhibitors of skin's degradation enzymes (collagenase and elastase) [13]. Secondly, the small lipophilic molecules that make up their composition grant easy penetration through the skin layers [14].

South Africa (SA) is home to an important and rich botanical diversity. The country boasts over 30,000 flowering species with high endemism and is ranked third in biodiversity in the world [15,16]. A significant fraction of aromatic plant species contributes to this rich heritage. To date, oil-rich plant species recorded in South Africa belong to the Asteraceae family (2300 species), Rutaceae family (290 species), and Lamiaceae (235 species) family [16].

*Oncosiphon* Källersjö is an aromatic genus of the Asteraceae family and Anthemideae tribe that counts seven species. Some species of the genus were formerly classified in the *Pentzia* Thunb. and others in *Matricaria* L. genera. However, the *Oncosiphon* genus

**Citation:** Adewinogo, S.O.; Sharma, R.; Africa, C.W.J.; Marnewick, J.L.; Hussein, A.A. Chemical Composition and Cosmeceutical Potential of the Essential Oil of *Oncosiphon suffruticosum* (L.) Källersjö. *Plants* **2021**, *10*, 1315. https://doi.org/ 10.3390/plants10071315

Academic Editors: Daniela Rigano, Hazem Salaheldin Elshafie, Laura De Martino and Adriano Sofo

Received: 15 May 2021 Accepted: 24 June 2021 Published: 28 June 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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later arose due to the morphological differences recorded in the now-*Oncosiphon* species which were not present in the *Pentzia* genus. Most of the *Oncosiphon* species are native to the Greater Cape Floristic Region except for *O. piluliferum* (L.f.) Källersjö and *O. suffruticosus* (L.) Källersjö. These two species also grow in Australia and are respectively known as Globe Chamomile and Calomba Daisy. *Oncosiphon* species bear the Afrikaans name "stinkruid" which means stinkweed due to their pungent aroma. Among them, *O. piluliferum*, *O. suffruticosus*, and *O. africanum* are important materials of Cape Dutch ethnobotany and Khoi-San medicine [17].

The *O. suffruticosum* (L.) Källersjö herb features hairless and thin leaves (Figure 1). It bears a typical sharp and powerful scent like other *Oncosiphon* species. The herb grows up to 50 cm tall annually and is distributed in the southern part of Africa from the Western Cape to Namibia [18]. In traditional healing practices, oral administrations aim to treat asthma, gastric disorders, convulsions, diabetes, rheumatic fever, typhoid fever, colds, and influenza [19,20]. Additionally, the herb is used topically as a leaf poultice to treat scorpion stings and inflammation [20].

**Figure 1.** Photographs of *O. suffruticosum*. (**a**) Uprooted branch; (**b**) flower heads. These photographs were taken during the summer season (December, 2018) at the Cape Flats regions of Cape Town, South Africa.

Since time immemorial, plants have been renowned sources of bioactive materials used in traditional therapies and a reservoir for innovative cures in modern medicine. The use of plants ranges from culinary preparations, medicine, to perfume compositions [21]. However, only a few SA medicinal plants are explored commercially [22] and investigated scientifically [20]. According to the literature, the essential oil of *O. suffruticosum* has never been studied before. In the quest to explore the South African flora for novel cosmeceutical ingredients, the aim of the present research was to elucidate the chemical composition and study the biological studies, antimicrobial activity, antioxidant capacity, antityrosinase activity, and photoprotection of the essential oil of *O. suffruticosum*.
