TAXONOMIC STUDIES AND GENERIC DELIMITATION IN THE GRASS SUBTRIBE Sorghinae. Moffat Pinkie Setshogo A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy University of Edinburgh March 1997 Dedicated to the memory of my father, Tonkana, and to my mother, Kerileng. Acknowledgements. This work was carried out under the supervision of Dr. P.M. Smith. I wish to express my sincere gratitude to him for the advice and assistance throughout the progress of the study. I also want to thank Dr. C.E. Jeffree who has been very supportive and proof read a substantial portion of the thesis. I am indebted to the University of Botswana for the financial support and for offering me a study leave to enable me to carry out this study. The work was carried out at the Department of Botany, University of Edinburgh, as well as at the Royal Botanic Garden, Edinburgh. I would like to extend my thanks to the authorities of both institutions, and their staff, who offered help in many ways. My collection of living material was cared for by Messrs Billy Adams and Bob Astles. I wish to thank them for their help. My thanks also go to members of the photographic unit of ICMB, particularly John Anthony, Dave Haswell and Frank Johnston, for their help. Mr. John Findlay (Botany Department) gave me guidance with my SEM work, for which I am grateful. I am indebted to the Directors of various herbaria who loaned me specimens. Helen Hoy and Marisa Main were in charge of the Edinburgh side of these loans. Also of help were various seed sources around the world. I thank Mr. W.M.M. Eddie, who helped me with PANKEY, NTSYS, PAUP and MacClade computer programmes used in the numeric analysis. Dr. T. Cope and Dr. G.V. Pope are well remembered for their help and useful suggestions during my visits to RBGKew. Mrs Zoë Cooke and Mr Bill Eddie, fellow PhD students deserve special thanks for their useful assistance, fruitful discussions and for providing the 'buzz' in the lab. My mother, brothers and sisters have been a source of inspiration for my studies here. I pay my deep respect and thanks to them. Lastly, I wish to express a very special thank you to my wife, Dineo, and son, Reba, who sacrificed a lot of their emotions to enable me to see my studies to the end. Tanki betsho! LV Contents. Page Title page. Declaration. Acknowledgements. lv Abstract. x Chapter 1. Introduction. 1 1.1. Project background. 1 1.2. Aims and objectives. 2 1.3. Sampling procedure. 3 Chapter 2. Classification. 9 2.1. Introduction. 9 2.2. Sorghinae and related Andropogoneae subtribes. 9 2.3. Taxonomic History of Sorghinae. 12 2.4. Nomenclatural origins of Sorghinae genera. 18 2.4.1. Hemisorghum C.E. Hubbard. 18 2.4.2. Spathia Ewart. 18 2.4.3. Pseudodichanthium Bor. 18 2.4.4. Cleistachne Benth. 19 2.4.5. Sorghum (L.) Moench. 20 2.4.6. Chrysopogon Trin. 21 2.4.7. Sorghastrum Nash. 22 2.4.8. Vetiveria Bory. 22 2.4.9. Euclasta Franch. 23 2.4.10. Pseudosorghum A..Camus. 24 2.4.11. Asthenochloa BUse. 25 2.4.12. Capillipedium Stapf. 25 2.4.13. Dichanthium Willemet. 25 2.4.14. Bothriochloa Kuntze. 26 2.5. Species of economic importance. 28 Chapter 3. Concepts of categories and generic delimitation in the Sorghinae. 30 3. 1. Introduction. 30 3.2. The subtribe concept. 30 3.3. The genus concept. 31 3.4. The species concept. 33 3.5. Subspecies. 36 3.6. Variety. 38 3.7. Race. 39 3.8. Generic delimitation in the Sorghinae. 40 3.8.1. The Sorghastrae. 45 3.8.2. The Bothriochloastrae. 50 3.9. Conclusion. 53 Chapter 4. Macromorphology. 54 4.1. Introduction. 54 4.2. Sources of plant material. 54 4.3. Evaluation of principal taxonomic characters. 54 4.3.1. Longevity and perennating organs. 54 4.3.2. Culms. 55 4.3.3. Leaves. .55 4.3.4. Sheath. 56 4.3.5.Ligule. 56 4.3.6. Inflorescence. 57 4.3.7. Racemes. 63 4.3.8. Spikelets. 65 4.3.9. Sessile spikelet. 67 4.3.10. Pedicellate spikelet. 67 4.3.11. Homogamous spikelet pairs. 68 4.3.12. Callus. 69 4.3.13.Glumes. 69 4.3.14. Lower lemma. 71 4.3.15. Upper lemma. 72 4.3,16.Palea. 72 4.3.17. Awn. 73 Vi 4.3.18. Lodicules. 73 4.3.19. The androecium. 74 4.3.20. The gynoecium. 74 Chapter 5. Micromorphological studies with the Scanning Electron Microscope. 82 5.1. Introduction. 82 5.2. Materials and Methods. 82 5.3. Glume pits in the genera Bothriochloa and Dichanthium. 83 5.3.1. Introduction. 83 5.3.2. Glume pits. 83 5.3.3. Role of glume pit in cleistogamy. 88 5.3.4. Use of glume pit as a taxonomic character. 89 Chapter 6. Anatomical investigation of the leaf blade. 94 6.1. Introduction. 94 6.2. Materials and Methods. 95 6.2.1. Preparation. 95 6.2.2. Rinsing. 95 6.2.3. Dehydration. 95 6.2.4. Infiltration. 96 6.2.5. Embedding. 97 6.2.6. Sectioning. 97 6.2.7. Mounting ribbons. 97 6,2.8. De-waxing. 97 6.2.9. Staining. 98 6.2.10. Mounting. 98 6.2.11. Cleaning slides. 98 6.3. Evaluation of characters observed. 99 6.3.1. Outline of the leaf lamina in transverse section. 99 6.3.2. Epidermis. 99 6.3.3. Bulliform cells. 100 6.3.4. Vascular bundles. 101 6.4. Discussion. 101 6.5. Conclusion. 104 Vii Chapter 7. Numeric analysis. 118 7.1. Introduction. 118 7.2. Phenetics. 119 7.2.1. Procedure. 120 7.2.2. Conclusion. 123 7.3. Phylogenetics. 127 7.3.1. Some concepts associated with cladistics. 129 7.3.2. Cladogram interpretation and evaluation. 132 7.3.3. Procedure. 134 7.4. General Discussion. 138 Chapter 8. Taxonomic descriptions. 140 8.1. Introduction. 140 8.2. Sorghinae Nees, Bluff & Schuaer. 141 8.2.1. Cleistachne Benth. 144 8.2.2. Sorghastrum Nash. 146 8.2.3. Asthenochloa Büse. 164 8.2.4. Hemisorghum C.E. Hubbard. 165 8.2.5. Sorghum (L.) Moench. 169 8.2.6. Pseudosorghum A. Camus. 185 8.2.7. Chrysopogon Trin. 187 8.2.8. VetiveriaBory. 210 8.2.9. Pseudodichanthium Bor. 221 8.2.10. Capillipedium Stapf. 223 8.2.11. Spathia Ewart. 233 8.2.12. Bothriochloa Kuntze. 235 8.2.13. Euclasta Franch. 258 8.2.14. Dichanthium Willemet. 263 Chapter 9. Distribution and ecogeography of the Andropogoneae and the Sorghinae. 278 9.1. The Andropogoneae. 278 9.2. The Sorghinae. 281 9.2.1. Cosmopolitan genera. 281 Viii 9.2.2. Discontinuous genera. 292 9.2.3. Endemic genera. 297 Chapter 10. References. 300 Chapter 11. Appendices. 314 ix Abstract. Genera and species of the grass subtribe Sorghinae were investigated. This study covered taxa from the whole range of their morphological variation and geographic distribution. In order to make the study feasible in the time permitted, a representative sample was chosen. Parameters used in choosing this sample are outlined in Chapter 1. The objective of the study was to determine and ascertain generic boundaries in the subtribe and hence reveal relationships between them. Fourteen genera are recognised in the subtribe. These are Asthenochloa, Bothriochloa, Capillipedium, Chrysopogon, Cleistachne, Dichanthium, Euclasta, Hemisorghum, Pseudodichanthium, Pseudosorghum, Sorgahstrum, Sorghum, Spathia and Vetiveria. They were confirmed to form clearly distinct genera despite suggestions by some authors to the contrary, some of whom have advocated merging some genera in the subtribe. The genera divide into two groups. The first group consists of Sorghum and allies, while the second group is centred around Dichanthium (Chapter 3). Numeric analysis were used to highlight both phenetic and phylogenetic relationships between the genera (Chapter 7). The phenetic analysis broadly revealed a somewhat similar picture to the one I held. Species of the same genus cluster in the same place. Also those genera that are least similar separate at low phenon levels. The cladogram produced, however, was totally different from my intuitive classification of the subtribe. Formal taxonomic descriptions incorporating keys and specimens seen can be found in Chapter 8. An attempt was made to document a lot of information about the taxa studied, e.g., chromosome number(s), even if these were not a direct result of the research. A new combination in Euclasta, E. oligantha (Hotchst. ex Steud.) M.P. Setshogo, was recognised (Appendix 11.2). Three factors consistently affecting the taxonomy of the subtribe are suggested to be (i) intergeneric hybridisation in the generic complex Bothriochloa-Capillipedium- Dichanthium; (ii) man induced interspecific hybridisation in Sorghum and (iii) specific complexes whose member species overlap morphologically (Chapter 3). x Several sources of evidence were tapped to address these problems. These were the use of micro- and macro-morphology and anatomy. The research was based on the use of herbarium material as well as living plants. Leaf anatomy confirmed the C4 physiological anatomy associated with the grasses (Chapter 6). Scanning Electron Microscopy (SEM) was used to study glume pits in the genera Bothriochloa and Dichanthium (Chapter 5). Distribution and ecogeography revealed that the subtribe Sorghinae occurs in the tropics and subtropics of the Old World, with a high concentration of species and genera in the Indian subcontinent (Chapter 9). Except for a few species of Bothriochloa, Chrysopogon and Sorghum reportedly introduced into the Western Hemisphere, only Sorghastrum, has a substantial representation there.