A Systematic Study of Leonotis (Pers.) R. Br. (Lamiaceae) in Southern Africa
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A systematic study of Leonotis (Pers.) R. Br. (Lamiaceae) in southern Africa by Wayne Thomas Vos Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy Department of Botany University of Natal Pietermaritzburg February 1995 11 To Unus and Lorna Vos III Preface The practical work incorporated in this thesis was undertaken in the Botany Department, University of Natal, Pietermaritzburg, from January 1990 to May 1994, under the guidance of Mr. T.J. Edwards. I hereby declare that this thesis, submitted for the degree of Doctor of Philosophy, University of Natal, Pietermaritzburg, is the result of my own investigations, except where the work of others is acknowledged. Wayne Thomas Vos February 1995 IV Acknowledgements I would like to thank my supervisor Mr. T.l Edwards and co-supervisor Prof. 1 Van Staden and Dr. M.T. Smith for their tremendous support, assistance on field trips and for proof reading the text. I am grateful to the members of my research committee, Mr. T.l Edwards, Dr. M. T. Smith, Prof. 1 Van Staden, Prof. R.I. Yeaton and Dr. lE. Granger for their suggestions and guidance. I acknowledge the University of Natal Botany Department and The Foundation of Research and Development for fmancial assistance. A special thanks to my parents, Trelss McGregor and Mrs. M.G. Gilliland, for their tremendous support and encouragement. The translation of the diagnosis into latin by Mr. M. Lambert of the Classics Department, University of Natal, and the German translation by Ms. C. Ackermann, are gratefully acknowledged. Sincere thanks are extended to the staff of the Electron Microscope Unit of the University of Natal, Pietermaritzburg, for their assistance. The assistance of Dr. M. T. Smith with essential oil and nectar analyses and Dr. R. Beckett is greatly appreciated. I would also like to thank Prof. A.E. van Wyk of the Schweickerdt Herbarium, University of Pretoria, for valuable discussion, Dr. F. Getliffe-Norris for the photograph of Nectarinia afra (Linnaeus), Dr. C.H. Stirton and Mr. A. Nicholas for literature from Kew, Andy Whittington of the Natal Museum for insect identification, Mrs. D. Fourie of The National Botanical Institute, Pretoria, and Mr. H. Kolberg of The National Herbarium of Namibia, for the provision of Leollotis (pers.) R. Br. nutlets. I extend my gratitude to Neil Crouch, Anton Schmidt, Ivan Thrash and Brent Baxter for assistance in the field. Herbaria of the following institutions are acknowledged for the loan of specimens: British Museum (BM); Bolus Herbarium (BOL); Bulawayo Herbarium, National Museum of Zimbabwe (BUL); University of Zimbabwe, v Harare (CAH); Royal Botanic Gardens, Edinburgh (E); Geneve Herbarium (G); The National Herbarium of Botswana (GAB); Albany Museum (GRA); Miinchen Herbarium (M); Missouri Botanical Garden (MO); Compton Herbarium, National Botanic Gardens, Kirstenbosch (NBG); Natal Herbarium, Durban (NH); Natal University, Pietermaritzburg (NU); Royal Botanic Gardens, Kew (K); Museum of Natural History, Paris (P); National Herbarium of Pretoria (PRE); Swedish Museum of Natural History, StOGkholm (S); South African Museum, Kirstenbosch (SAM); Natural History Museum, Wien (W); National Herbarium of Namibia (WIND) and Institute for Systematic Botany, Ziirich University (Z). VI Abstract The southern African species of Leonotis (Pers.) R. Br. are revised. Nine taxa are recognised including a new species and two new subspecies. A multidisciplinary approach was adopted involving: floral, vegetative, seedling and fruit morphology, karyology, palynology, pollination biology, phytogeography, phytochemistry and cladistics. Of these characters the most important in delimiting species is leaf morphology. Phytochemistry revealed qualitative and quantitative differences in essential oils between taxa. Germacrene is the dominant essential oil in seven species, particularly in L. dubia E. Mey. and L. Ilepetifolia (L.) R. Br. Caryophyllene dominates in L. randii S. Moore. Although certain species have characteristic aromas, no inter-specific differences are apparent in the levels of a-copaene, the dominant volatile essential oil extracted with Tenax. Essential oil data is in partial agreement with the phylogeny and species concepts presented in this document. Omithophily accounts for most fruit set in perennial species but in the annual species (L. nepetifolia) autogamy prevails. Neither omithophily nor entomophily improved nutlet vigour which was gauged from nutlet germination. Leonotis species are predominantly pollinated by a variety of sunbirds, although bees are also involved. Nectar is sucrose-dominant in perennial species but hexose-dominant in the annual. The majority of species are concentrated along the eastern seaboard with the eastern Cape forming the centre of diversity. The widespread distribution and tropical affinities of L. leonurus (L.) R. Br., suggest an origin for the genus in tropical Africa. Migration to southern Africa and subsequent speciation are suggested. Habitat diversity and edaphic conditions probably played an important role in the evolution of narrowly distributed xerophytic species. Vll A cladistic analysis re-emphasised that Leonotis is a monophyletic group of closely related species. The lack of floral divergence in perennial species indicates the constraints imposed by ornithophily. The annual, L. nepetifolia, is highly derived and displays numerous autapomorphies. The morphology, distribution and tropical affmities of L. leollurus are interpreted as pleisiomorphic. The proposed phylogeny is reasonably compatible with phytogeographic data. Vlll Table of contents Page Dedication I Preface 11 Acknowledgements 111 Abstract V Table of contents V1l List of tables and figures IX Chapter 1. Introduction 1 Chapter 2. Material and methods 5 Chapter 3. Leaf morphology 20 Chapter 4. Leaf and stem anatomy 35 Chapter 5. Calyx morphology 46 Chapter 6. Inflorescence and floral morphology 53 Chapter 7. Fruit morphology 67 Chapter 8. Seedling morphology 73 Chapter 9. Palynology 77 Chapter 10. Karyology 80 Chapter 11. Chemosystematics of essential oils 82 Chapter 12. Pollination biology 97 Chapter 13. Habit, habitat and phytogeography 110 Chapter 14. Cladistic analysis 124 IX Chapter 15. Formal taxonomy 130 The genus Leonotis 130 Key to the species of Leonotis 132 Species' descriptions: 134 Leonotis leonurus (L.) R. Br. 134 Leonotis randii S. Moore 144 Leonotis schillzii Giirke 149 Leonotis nepetifolia (L.) R. Br. 154 Leonotis ocymifolia (Burm. f.) I warsson ssp. ocymifolia W.T. Vos and TJ. Edwards 162 Leonotis ocymifolia (Burm. f.) I warsson ssp. transvaalensis W. T. Vos and T.J. Edwards 169 Leonotis dubia E. Mey. 174 Leonotis paucijlora W.T. Vos and T.J. Edwards 181 Leonotis intermedia Lind!. 185 Bibliography 200 x List of tables and figures List of tables Page Table 1. Major revisions of Leonotis recognised the following species 4 Table 2. Leaf characters of Leolwtis 24 Table 3. Anatomical characters of the flowering stem of Leonotis 38 Table 4. Dimensions from transverse sections of Leonotis leaves 38 Table 5. Calyx characters of Leonotis 48 Table 6. Inflorescence characters of Leonotis 57 Table 7. Inflorescence characters of Leollotis 58 Table 8. Corolla characters of Leonotis 60 Table 9. Corolla characters of Leollotis 61 Table 10. Nutlet characters of Leonotis 71 Table 11. Mean hypocotyllength and cotyledon shape of Leollotis seedlings 75 Table 12. Data matrix showing the percentage area occupied by peaks of various retention times of essential oils in fresh (1991) and preserved (1915- 1971) specimens of L. leollurus 92 Table 13. A comparison of selected essential oils of Leollotis leollurus in two independent studies 94 Table 14. Insects collected on Leonotis during 1992 and 1993 99 Table 15. Records of sunbird (Nectarinidae) visits to Leonotis species 100 Table 16. Floral and nectar characteristics of perennial and annual Leonotis species 106 Table 17. Plant height, altitude and climatic conditions of Leollotis 116 Table 18. Soil and habitat conditions of Leonotis 117 Table 19. Leollotis data matrix employed in cladogram computation 125 Xl List of figures Page Figure 1. Deftnition and measurement of the corolla and inflorescence of Leonotis 9 Figure 2. Leaf variation in Leonotis 22 Figure 3. Leaf variation in Leonotis 23 Figure 4. Lamina length and width of Leollotis species 25 Figure 5. Floral leaves of Leollotis 27 Figure 6. Abaxial leaf indumentum of Leollotis 28 Figure 7. Trichomes, stomata and surface sculpturing of Leollotis leaves 29 Figure 8. Leaf venation of Leonotis 30 Figure 9. Transverse sections of the stem of Leollotis 37 Figure 10. Transverse sections of the petioles of Leollotis 40 Figure 11. Transverse sections of the midrib of Leollotis leaves 41 Figure 12. Transverse sections of Leonotis leaves 42 Figure 13. Crystal types found in the flowering stems and leaves of Leollotis44 Figure 14. Lateral and frontal views of the calyx of Leonotis 49 Figure 15. Calyx venation of Leonotis 50 Figure 16. Schematic diagrams of Leonotis inflorescences 54 Figure 17. Outlines of Leollotis verticillasters 55 Figure 18. Corolla morphology of Leonotis 56 Figure 19. Non-glandular trichomes of Leollotis 62 Figure 20. Pericarp cell patterns of Leollotis 69 Figure 21. Morphology of Leonotis nutlets 70 Figure 22. Seedling morphology of Leonotis 74 Figure 23. Leonotis pollen 79 Figure 24. Thin-layer chromatography plates of essential oils in Leollotis comparing steam distillation with direct extraction methods, essential oil standards and