Othonna cakilefolia DC.
Common names: sea-rocket othonna (Eng.); bobbejaankool (Afr.)
One of only three Othonna species with pink to magenta florets; its striking, pink daisy-like flower heads, make it a desirable member of the genus.
Fig. 1. Habit of Othonna cakilefolia showing trisect to pinnatisect leaves with narrow, obtuse lobes and pink daisy-like flower heads. (Photo Nick Helme)
Othonna cakilefolia is a herbaceous geophyte, up to 500 mm high, arising from a short, thick, tuberous root. The annual stems bear leathery to sub-succulent, ovate to elliptic, rarely linear, trisect to pinnatisect leaves.
Fig. 2. The trisect to pinnatisect leaves of Othonna cakilefolia. (Photo Adam Harrower)
Flower-heads are solitary or in clusters of 3, sometimes with lateral axes, radiate; ray florets magenta or pink, sometimes darker basally; disc florets magenta; involucral bracts 10 or 12.
Fig. 3. Othonna cakilefolia capitula with magenta disc florets and pink to magenta ray florets. (Photo Nick Helme)
Fruits with stiff short hairs on the ribs that release mucilage when wetted and a pappus of beige, barbellate bristles that aids in dispersal (Magoswana et al. 2016, 2019).
Fig. 4. Othonna cakilefolia fruits with stiff short hairs on the ribs and barbellate bristles. (Photo Nick Helme)
Othonna cakilefolia is currently assessed as Vulnerable (VU) in the Red List of South African plants (Raimondo 2007). However, the species has recently been recorded by botanist Nick Helme (pers. communication June 2019) as quite common but seemingly very local on loamy shales.
Distribution and habitat
Othonna cakilefolia is a poorly collected species known from a few localities between Kamieskroon and Holrivier, with an isolated collection near Lutzville along the west coast, on sandy flats or quartz outcrops below 500 m (Rowley 1994, Magoswana et al. 2019).
Fig. 5. The tuberous root of Othonna cakilefolia. (Photo Nick Helme)
Derivation of name and historical aspects
The genus name Othonna is probably from the Greek word, othonne, for linen or cloth, referring to the soft leaves of some species (Jackson 1990). This species was named by De Candolle, in 1838, for the resemblance of its leaves to those of the genus Cakile, commonly called sea rocket (Rowley 1979).
The genus Othonna L. comprises ± 90 species excluding the recently segregated genus Crassothonna B.Nord. (Leistner 2001, Nordenstam 2007, 2012, Manning & Goldblatt 2012, Glavich 2016, Magoswana et al. 2019). Species of Othonna are succulent or sub-succulent perennial herbs or shrubs with more or less dorsiventrally flattened leaves, radiate or disciform capitula with female-sterile disc florets and female marginal florets, with a beige or reddish pappus that is sometimes accrescent (Leistner 2001, Manning & Goldblatt 2012, Nordenstam 2012, Glavich 2016, Magoswana et al. 2016, 2019). The genus is recognized by the presence of undivided (or minutely bifid) styles in disc florets (Nordenstam 2012, Magoswana et al. 2019).
Othonna cakilefolia, O. lilacina and O. rosea are the only species in the genus with pink to magenta ray florets. They are distinguished by leaf shape and number of involucral bracts. O. cakilefolia with trisect to pinnatisect leaves, with narrow, obtuse lobes, and 10 to 12 involucral bracts. In the last-named 2 species, the leaves are entire or variously toothed to pinnatisect (Manning & Goldblatt 2010, Magoswana et al. 2019).
Othonna cakilefolia grows on small outcrops of white quartz or sandy soils and loamy shales, flowering in winter and spring, from June to September. The inflorescence dies off during the dormant season. Flowers are bee and insect pollinated.
None recorded. However, it has horticultural potential.
Growing Othonna cakilefolia
Othonna cakilefolia is a challenge to cultivate, is rarely seen in cultivation and propagative material is not often available. Seed should be sown in autumn in a well-drained, sandy loam soil mix suitable for succulent plants and covered lightly to hold them in place. Keep the soil moist but not wet, and place them in a warm, sheltered position. Seeds should germinate in about 2 weeks (Harris 2014, Sutty 2017). Seedlings produce 2 fleshy cotyledons and nothing further until, after a long period when the cotyledons may or may not have withered away, new growth, with true leaves, appears from a lateral bud on the tuberous stem (Rowley 1979). Transplant with care because the plants break easily, into a pot that is deep enough to accommodate its tuberous root. Use a similar soil mix, with bonemeal as a fertilizer. Grow them in a sunny position, with moderate water in autumn, winter and spring and a completely dry summer. It could be grown in a sunny rockery in water-wise gardens in low rainfall, winter-rainfall areas, but in other areas it is better suited to containers and placed in a sunny, well-ventilated position.
- Glavich, T. 2016. Beginner’s guide to geophytic Othonna. Cactus and Succulent Journal 88: 89–91.
- Harris, S. 2014. Othonna retrofracta (L.) Jacq. (Asteraceae). PlantZAfrica. Online. http://pza.sanbi.org/othonna-retrofracta
- Jackson, W.P.U. 1990. Origins and meanings of names of South African plant genera. University of Cape Town.
- Leistner, O.A. (ed.). 2000. Seed plants of southern Africa: families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Magoswana, S.L., Boatwright, J.S., Magee, A.R. & Manning, J.C. 2016. A taxonomic revision of Gymnodiscus (Asteraceae: Senecioneae: Othonninae), a Greater Cape Floristic Region endemic. South African Journal of Botany 106: 71–77.
- Magoswana, S.L., Boatwright, J.S., Magee, A.R. & Manning, J.C. 2019. A taxonomic revision of the Othonna bulbosa group (Asteraceae: Senecioneae: Othonninae). Annals of the Missouri Botanical Garden 104(4): 525.
- Manning, J.C. & Goldblatt, P. 2010. New synonyms and a new name in Asteraceae: Senecioneae from the southern African winter rainfall region. Bothalia 40 (1): 37–46.
- Manning, J. & Goldblatt, P. 2012. Plants of the Greater Cape Floristic Region 1: the Core Cape Flora. Strelitzia 29. South African National Biodiversity Institute, Pretoria.
- Nordenstam, B. 2007. Tribe Senecioneae. In J.W. Kadereit & C. Jeffrey, Kubitzki’s The families and genera of vascular plants Vol. 8. Springer, Heidelberg, pp. 208–24.
- Nordenstam, B. 2012. Crassothonna B. Nord., a new African genus of succulent Compositae-Senecionae. Compositae Newsletter 20, 70–77.
- Raimondo, D. 2007. Othonna cakilefolia D.C. National Assessment: Red list of South African plants version 2017.1. Accessed on 2020/02/04.
- Rowley, G. 1979. Othonna cakilefolia DC. The Cactus and Succulent Journal of Great Britain 41(2): 34.
- Rowley, G.D. 1994. Succulent compositae. A grower’s guide to the succulent species of Senecio & Othonna. Strawberry Press, California.
- Sutty, C. 2017. Othonna herrei Pillans (Asteraceae). PlantZAfrica. Online. http://pza.sanbi.org/othonna-herrei
Xichavo Mathebula and Luvo Magoswana
Acknowledgements: the authors thank Nick Helme and Adam Harrower for providing the images to illustrate this article.
Plant Type: Succulent
SA Distribution: Northern Cape, Western Cape
Soil type: Sandy, Loam
Flowering season: Spring, Winter
Flower colour: Purple, Pink, Yellow
Aspect: Full Sun, Morning Sun (Semi Shade), Afternoon Sun (Semi Shade)
Gardening skill: Challenging