Rotheca louwalbertsii is a slender, dainty plant with purplish blue flowers borne in long, terminal inflorescences. The individual flowers look almost like ballerinas in purple tutus dancing in the wind.
Rotheca louwalbertsii is a perennial herb with many erect, unbranched or sparsely branched, angular, annual stems arising from a woody, underground rootstock. The glabrous or pilose annual stems are usually up to 0.5 m, rarely up to 0.8 m tall. The leaves are arranged in threes (ternate), opposite or sometimes in whorls of 4, sessile or subsessile, glabrous or pilose; blade linear to narrowly elliptic, decreasing in size upwards. The apex of the leaves is acute, the base cuneate and the margin is entire. The leaf surfaces are dotted with numerous peltate hairs.
Light micrograph of the epidermis of the leaf of Rotheca louwalbertsii to show the 8-celled head of the peltate hair. (Scale bar = 50 µm)
|Scanning electron micrograph of the leaf surface of Rotheca louwalbertsii to illustrate the peltate hairs.
Flowering was recorded from October to March (May). The stems culminate in long, drawn-out inflorescences with the leaves gradually decreasing to bracts supporting the peduncles. The peduncles are also arranged in threes, one in the axil of each bract. The lower peduncles are the longest and often branched, bearing up to three flowers (dichasium/cyme), whereas the upper peduncles are shorter and mostly one-flowered. The whole compound inflorescence structure is known as a thyrse.
The calyx is green but often tinged purplish, fused to about halfway and with five free calyx lobes. The corolla appears as a ball on a short tube, opening up as a bilaterally symmetrical (zygomorphic) unit consisting of a short tube, four lateral lobes (two on each side) and a lower lip. The four lateral petals are pale purplish while the lower lip is dark purple marked with a white inverted Y-shaped pattern. Four stamens and the style, all purple, are inserted in the corolla throat, opposite the lower lip, long exserted and curved towards the lower lip. The stigma consists of two unequal lobes. The superior ovary is 4-lobed in the upper part. Only one or two, rarely three or four, of these lobes develop further into small, elongated, elliptic or oblong fruits (1- to 4-lobed drupe), much smaller than the elliptic to roundish black fruits of the sister species, R. hirsuta (= Clerodendrum triphyllum). The calyx is persistent in the fruiting stage.
Rotheca louwalbertsii is currently not regarded as a threatened plant species and is listed in the latest Red Data List as Least Concern (LC) (website: http://www.sanbi.org/redlist).
Distribution and habitat
The species occurs in the provinces of Limpopo, eastern part of North-West, Gauteng, Mpumalanga, the northern border of KwaZulu-Natal, and also in Swaziland and possibly Mozambique.
It is found in valleys, kloofs, mountains, hillsides and koppies in grassland and open woodland on sandy, stony or rocky soil.
The distributuon of Rotheca louwalbertsii in southern Africa.
click on map for enlarged view
Derivation of name and historical aspects
The earliest valid, and available name for a group of previously named Clerodendrum species was established as Rotheca by Rafinesque in 1836, who derived it from Latinizing two Malaysian names, cheriya, meaning small, and thekku, meaning teak.
The species name louwalbertsii was chosen in honour of Dr Louw Alberts, a well-known South African scientist and Christian. He held a Doctorate in Physics and was awarded three honorary doctorates. He was inter alia vice president of the then Atomic Energy Board, Director-General of the Department of Mineral and Energy Affairs, chairman of the board of the CSIR and chairman of the Suid-Afrikaanse Akademie vir Wetenskap en Kuns (an academy for science and art). He played a leading role in the peace initiatives during the 1990s. His philosophy about science and religion: ‘To me, the written word (the Bible) and the created word (natural science) have the same author—God—and a wonderful harmony exsists between the two'.
The genus Rotheca comprises about 30 species in the sub-Saharan region of Africa, with one species in tropical Asia, eastwards to the Molucca Islands, and one species introduced and naturalized in Madagascar and the Indian Ocean Islands (Fernandes 2005). About nine species are known from southern Africa.
Rotheca louwalbertsii was for a long time confused, misidentified and included in R. hirsuta (= Clerodendrum triphyllum ). Specimens of this taxon were already collected by Zeyher on the Magaliesberg, but it was only described as new in 1995 as Clerodendrum louwalbertsii ( Herman 1995). Based on certain morphological and molecular studies, some Clerodendrum species were transferred to Rotheca, which necessitated the new combination ( Herman & Retief 2002).
The genera Rotheca and Clerodendrum are distinguished as follows: in Rotheca, the flower buds are markedly asymmetrical, the corolla expanding abruptly on the lower side only, the anterior corolla lobe is frequently much larger than the other four corolla lobes; the anthers are basifixed and the stigma lobes are unequal. In Clerodendrum, the flower buds are symmetrical or, if asymmetrical, usually expanding abruptly on the upper side due to resupination (the flower buds turn upside down because the pedicels (flower stalks) are twisted through 180º), the anterior corolla lobe is only slightly (if at all) larger than the other corolla lobes; the anthers are versatile and the stigma lobes are equal.
R. louwalbertsii can be distinguished from R. hirsuta by the long, drawn-out terminal inflorescences (thyrsoid inflorescence) and the linear leaves. In R. hirsuta the flowers are arranged in cymes in the axils of the lower leaves and the leaves range from narrowly obovate to obovate to elliptic.
The white, inverted Y-shaped pattern on the purple lower corolla lip and the long exserted, curved stamens and style of R. louwalbertsii are adaptations to insect pollination. The underground rootstock is an adaptation for survival of unfavourable conditions such as the cold, dry winters of the Highveld, and veld fires.
Uses and cultural aspects
Nothing is known about the traditional or other uses of this plant as it was included under R. hirsuta for such a long time. It could be that many of the uses recorded for R. hirsuta are also applicable to R. louwalbertsii.
Growing Rotheca louwalbertsii
As in the case of Rotheca hirsuta, R. louwalbertsii is not in general cultivation, presenting a challenge to the keen gardener to create an environment to suit it.
References and further reading
- Burger, A. & Van Coller, R. 1992. Men at the forefront ….. and for peace: Louw Alberts. South African Panorama 37 (September/October 1992): 39–41.
- Cantino, P.D., Harley, R.M. & Wagstaff, S.J. 1992. Genera of Labiatae: status and classification. In R.M. Harley & T. Reynolds, Advances in Labiate Science. Royal Botanic Gardens, Kew.
- Fernandes, R. 2005. 129. Lamiaceae. In G.V. Pope & E.S. Martins, Flora zambesiaca 8,7: 61–153.
- Herman, P.P.J. 1995. A new species in the genus Clerodendrum (Verbenaceae). Bothalia 25: 100–102.
- Herman, P.P.J. 1998. The leaf anatomy of two Clerodendrum species (Verbenaceae). South African Journal of Botany 64: 246–249.
- Herman, P.P.J. & Retief, E. 2002. New combinations in the genus Rotheca in southern Africa (Lamiaceae). Bothalia 32: 81.
- Junell, S. 1934. Zur Gynäceummorphologie und Systematik der Verbenaceen und Labiaten. Symbolae botanicae upsaliensis 4: 1–219.
- National Red List of South African Plants. 2009. Interim Red Data Lists. website: http://www.sanbi.org/redlist.
- Pearson, H.H.W. 1912. Verbenaceae. In W.T. Thiselton-Dyer, Flora capensis 5,1: 218–225. Reeve, London.
- Retief, E. & Herman, P. 2008-02. Rotheca hirsuta. website: http://www.plantzafrica.com/plantqrs/rothechirs.htm.
- Steane, D.A. & Mabberley, D.J. 1998. Rotheca (Lamiaceae) revived. Novon 8: 204–206.
- Steane, D.A., Scotland, R.W., Mabberley, D.J., Wagstaff, S.J., Reeves, P.A. & Olmstead, R.G. 1997. Phylogenetic relationships of Clerodendrum s.l. (Lamiaceae) inferred from chloroplast DNA. Systematic Botany 22: 229–243.
P.P.J. Herman & E. Retief
National Herbarium, Pretoria