Professor Robert Scotland

Research interests

Biodiversity & Plant Systematics


Ipomoea batatas (Sweet Potato)

Two fundamental questions related to the origin and dispersal of sweet potato (Ipomoea batatas (L.) Lam.) remain unanswered. First, did the sweet potato evolve once or multiple times and what species were involved in its origin? Second, how did the sweet potato, a crop of American origin, come to be widespread in Polynesia before the arrival of the Europeans? Answering the first question requires knowledge of evolutionary relationships between the sweet potato and the species that are most closely related to it, often termed Crop Wild Relatives. Understanding this relationship is the key to unraveling the origin of this crop and has implications for food security because these CWRs constitute potential sources of genetic variation for future crop improvement. In the case of sweet potato, knowledge of these relationships is especially poor, even though it is a widely consumed crop  and an important resource for combating vitamin A deficiencies, estimated to affect over 190 million children worldwide. Answering the second question (how did the sweet potato come to be present in Polynesia before the Europeans first arrived?) requires the consideration of two additional questions. First, what is the possibility of sweet potato dispersing from its native range in America to Polynesia by natural means (i.e. wind, water, birds)? Secondly, when did sweet potato colonize Polynesia?

Summary of what we did:

Sweet potato is one of the world’s most widely consumed crops, yet its evolutionary history is poorly understood. In this paper we present a comprehensive phylogenetic study of all species closely related to sweet potato and address several questions pertaining to sweet potato that remained unanswered. Our research combined genome skimming and target DNA capture to sequence the whole chloroplasts and 605 single copy nuclear regions from 199 specimens representing sweet potato and all its crop wild relatives (CWRs). We present strongly supported nuclear and chloroplast phylogenies which demonstrate that sweet potato had an autopolyploid origin and Ipomoea trifida is its closest relative, confirming that no other extant species were involved in its origin. Phylogenetic analysis of nuclear and chloroplast genomes show conflicting topologies regarding the monophyly of sweet potato. The process of chloroplast capture explains these conflicting patterns, showing that Ipomoea trifida had a dual role in the origin of sweet potato, first as its progenitor and second as the species with which sweet potato introgressed so one of its lineages could capture an I. trifida chloroplast. In addition, we provide evidence that sweet potato was present in Polynesia in pre-human times. This, together with several other examples of long-distance dispersal in Ipomoea, negates the need to invoke ancient human-mediated transport as an explanation for its presence in Polynesia. These results have important implications for understanding the origin and evolution of a major global food crop and question the existence of pre-Columbian contacts between Polynesia and the American continent.

Article published in Current Biology, see commentary in NatureNew York Times and The Guardian.

I have recently focussed on a number of issues relative to the discovery process of new species as informed decisions concerning global taxonomic priorities demand some understanding of how species are discovered and revised. We have shown: that on average there is a lag period of 35 years between collection and description of new species (see here); a very large proportion of type specimens are collected by a few 'big hitter' collectors i.e. 50% of all type specimens have been collected by 2% of collectors (see here). We have also explored, for flowering plants, why the increasing number of authors associated with species discovery do not reflect an increase in taxonomic capacity as has been claimed in recent literature. Most recently we have shown that more than 50% of the world’s natural history collections may not have a correct name (see here).

Taxonomy & Foundation Monographs
The aim of our Foundation Monograph approach is to accelerate the pace of taxonomic revisions of large problematic groups. The first two foundation monographs were published in 2015 on Convolvulus (see here) and Ipomoea in Bolivia (see here).

Systematic theory
Over the last few years I have focussed on conceptual issues of homology, deep homology and parallelism. Most recently I have returned to the issue of morphological data and phylogeny, showing that ‘phylogenetic trees do not reliably predict feature diversity’ (see here) and also re-visiting compatibility and character congruence as methods for analysing morphological data.

Contact details

+44 (0) 1865 275059


Carruthers T, Muñoz-Rodríguez P, Wood JRI, & RW Scotland. In Press. The temporal dynamics of evolutionary diversification in Ipomoea. Molecular Phylogenetics & Evolution.

Carruthers T, & RW Scotland. 2020. Insights from empirical analyses and simulations on using multiple fossil calibrations with relaxed clocks to estimate divergence times Molecular Biology Evolution msz310

Wood JRI, Muñoz-Rodríguez P, Williams BRM & RW Scotland. 2020. A foundation monograph of Ipomoea (Convolvulaceae) in the New World. Phytokeys.

Carruthers, T. M.J. Sanderson & R.W. Scotland The implications of lineage-specific rates for divergence time estimation. Systematic Biology.

Muñoz-Rodríguez, P., Carruthers, T., Wood, J.R.I. et al. A taxonomic monograph of Ipomoea integrated across phylogenetic scales. Nat. Plants 5, 1136–1144 (2019) doi:10.1038/s41477-019-0535-4

Muñoz-Rodríguez, P., Carruthers, T. et al 2018. Reconciling Conflicting Phylogenies in Origin of Sweet Potato & Dispersal to Polynesia. Current Biology.

Wood JRI, Muñoz-Rodríguez P, Degen R, Scotland RW (2017) New species of Ipomoea (Convolvulaceae) from South America. PhytoKeys 88: 1-38.

Wood, J.R.I. & R.W. Scotland 2017. A new species of Strobilanthes (Acanthaceae) from Western Thailand.  NAT. HIST. BULL. SIAM SOC. 62 (1): 29–34. 

Wood, J.R.I. & R.W. Scotland. In press. Notes on Ipomoea L. (Convolvulaceae) in Cuba and neighbouring Islands with a checklist of species found in Cuba. Kew Bulletin.

Wood, J.R.I. & R.W. Scotland. 2017. Misapplied names, synonyms and new species of Ipomoea (Convolvulaceae) from South America. Kew Bulletin 72(9): 1-26.

Wood, J.R.I. & R.W. Scotland. 2017. Notes on Ipomoea (Convolvulaceae) from the Amazonian periphery. Kew Bulletin 72(10):1-18.

Wood, J.R.I.,  Vasconcelos, L.V., Simão Bianchini, R. & R.W. Scotland. 2017. New species of Ipomoea (Convolvulaceae) from Bahia. Kew Bulletin 72(8): 1-20.

Wood, J.R.I., de Arrúa, R.D., de Rojas, G.D. & R.W. Scotland 2016. Two overlooked species of Ipomoea L. (Convolvulaceae) from Paraguay. Kew Bulletin 71: 25.

Wood, J.R.I., C. Urbanetz, and R.W. Scotland, Ipomoea pantanalensis, a new species of Ipomoea L. (Convolvulaceae) from the Pantanal, Brazil. Kew Bulletin, 2016. 71(1): p. 1-3.

Mitchell, T.C., Williams, B.R.M., Wood, J.R.I., Harris, D.J., Scotland, R.W. & M.A. Carine. 2016. How the temperate world was colonised by bindweeds: biogeography of the Convolvuleae (Convolvulaceae). BMC Evolutionary Biology 16 (1), 1.

Scotland, R.W. & Steel, M. 2015. Circumstances in Which Parsimony but not Compatibility will be Provably Misleading. Systematic Biology 64(3): 492-504.

Goodwin, Z.A., Harris, D.J., Filer, D., Wood, J.R.I. & R.W. Scotland. 2015. Widespread mistaken identity in tropical plant collections. Current Biology 25(22): 1066-1067.

Khoury, C.K., Heider, B., Castañeda-Alvarez, N.P., Achicanoy, H.A., Sosa, C.C., Miller, R.E., Scotland, R.W., Wood, J.R.I., Rossel, G., Eserman, L.A., et al. 2015. Distributions, ex situ conservation priorities, and genetic resource potential of crop wild relatives of sweetpotato [Ipomoea batatas (L.) Lam., I. series Batatas]. Front. Plant. Sci. 6, 251.

Wood, J.R.I., Carine, M.A., Harris, D.J., Wilkin, P., Williams, B.R.M. & R.W. Scotland. 2015. Ipomoea (Convolvulaceae) in Bolivia. Kew Bulletin 70(31): 1-124. 

Wood, J.R.I., Williams, B.R.M., Mitchell, T.C., Carine, M.A., Harris, D.J. & R.W. Scotland. 2015. A foundation monograph of Convolvulus. Phytokeys 51: 1-282.

Bebber, D.P., Polaszek, A., Wood, J.R.I., Barker, C. & R.W. Scotland. 2014. Taxonomic capacity and author inflation. New Phytologist 202: 741–742

Bebber, D. P., Wood, J.R.I., Barker, C. & R.W. Scotland. 2014. Author inflation masks global capacity for species discovery in flowering plants. New Phytologist 201: 700–706.

Williams, B., Mitchell, T., Wood, J.R.I., Harris, D., Scotland, R.W. & M.A. Carine. 2014. The process of integrating DNA sequence data in a monographic study of Convolvulus. Taxon 63(6): 1287-1306.

Hay, A., Pieper, B., Cooke, E., Mandáková, T., Cartolano, M., Tattersall, A., Dello Ioio, R., McGowan, S., Barkoulas, M.,Galinha, C., Rast, M., Hofhuis, H., Then, C., Plieske, J., Ganal, M., Mott, R., Martinez-Garcia, J., Carine, M., Scotland, R.W., Gan, X., Filatov, D., Lysak, M. & M. Tsiantis. Cardamine hirsuta: a versatile genetic system for comparative studies 2014. The Plant Journal 78(1): 1-15. 

Kelly, S., Grenyer, R. & R.W. Scotland. 2014 Phylogenetic trees do not reliably predict feature diversity. Diversity & Distributions. 20: 600-612. 

Waters, M.T., Tiley, A.M.M., Kramer, E.M., Meerow, A.M., Langdale, J.A. & R.W. Scotland.  2013. The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls. The Plant Journal 74: 615-625. 

Wood, J.R.I, Williams, B.P. & R.W. Scotland, R.W. 2012. Diceratotheca, a new genus of Acanthaceae from Thailand Kew Bulletin. 67(4) 687-695.

Scotland, R.W. & J.R.I. Wood. 2012 Accelerating the pace of taxonomy. Trends in Ecology and Evolution 27(8): 415-416.  

Bebber, D.P., Carine, M.A., Davidse, G., Harris, D.J., Haston, E.M., Penn, M.G., Cafferty, S., Wood J.R.I. & R.W. Scotland. 2012. Big hitting collectors make massive and disproportionate contribution to the discovery of plant species. Proc. R. Soc. B. 279: 2269-2274.

Scotland, R.W. 2011. What is parallelism? Evolution and Development 13(2): 214-227 

Bebber, D.P., Carine, M.A., Wood, J.R.I., Wortley, A.H., Harris, D.J., Prance, G.T., Davidse, G., Paige, J.. Pennington, T.D., Robson, N.K.B., & R.W. Scotland. 2010. Herbaria are a major frontier for species discovery. PNAS. 107(51): 22169-22171 

Huayla, H., Scotland, R.W. & J.R.I.Wood. 2010. Further notes on a rare species of Selaginella (Pteridophyta-Selaginellaceae) from the Cerrados of Eastern Bolivia. Edinburgh Journal of Botany 67: 69-73 

Scotland, R.W. 2010. Deep Homology: a view from systematics. BioEssays 32: 438-449.

Wood J.R.I. & R.W. Scotland 2009. New and little known species of Strobilanthes (Acanthaceae) from India and South East Asia. Kew Bulletin 64: 3-47.

Bennett, J.R., Wood, J.R.I. & R.W. Scotland. 2008. Uncorrelated variation in widespread species: Species delimitation in Strobilanthes echinata Nees (Acanthaceae) Botanical Journal of the Linnean Society. 156 (1): 131-141.

Wortley, A.H., Harris, D.J. & R.W. Scotland. 2007. On the Taxonomy and Phylogenatic Position of Thomandersia. Systematic Botany 32(2): 415–444.

Bebber, D.P., Marriott, F.H.C., Gaston, K.J., Harris S.A. and R. W. Scotland. 2007. Predicting unknown species numbers using discovery curves. Proc. R. Soc. B. 274: 1651-1658.

Bebber, D.P., Harris, S.A., Gaston, K.J. & R.W. Scotland. 2007. Ethnobotany, plant discovery and the first written records of UK flowering plants. Global Ecology and Biogeography. 16: 103-108.

Wood, J.R.I. & R.W. Scotland. 2006. Some notes on the Strobilanthes pensteminoides (Acanthaceae) complex in China, India and South East Asia. Kew Bulletin 61: 5-16.

Wortley, A.H. & R.W. Scotland. 2006. The effect of combining molecular and morphological data in published phylogenetic analyses. Systematic Biology 55(4): 677-685.

Deng Y.F., Wood J.R.I. & R.W. Scotland. 2006. New and Reassessed species of Strobilanthes  (Acanthaceae) in the Flora of China. Botanical Journal of the Linnean Society 150: 369-390.

Wortley, A.H. & R.W. Scotland. 2006. Determining the potential utility of datasets for phylogeny reconstruction. Taxon 52(2): 431-442.

Wortley, A.H., Scotland, R.W. & P.J. Rudall. 2005. Floral anatomy of Thomandersia (Lamiales), with particular reference to the nature of the retinaculum and extra-nuptial nectaries. Botanical Journal of the Linnean Society. 149: 469-482. 

Wortley, A.H., Rudall, P.J., Harris, D.J. & Scotland, R.W. 2005. How much data are needed to resolve a difficult phylogeny? Case study in Lamiales. Systematic Biology 54 (5): 697-709.

Olmstead, R.G. & R.W. Scotland. 2005. Molecular & Morphological Datasets. Taxon 54(1): 7-8.

Harrison, C.J., Corley, S.B., Moylan, E.C., Alexander, D.L., Scotland, R.W. & J.A. Langdale. 2005. Independent recruitment of a conserved developmental mechanism during leaf evolution. Nature 434: 509-514.

Scotland, R.W. & M.J. Sanderson. 2004. The significance of few versus many in the tree of life. Science 5658: 643.

Moylan, E.C., J.R. Bennett, M.A. Carine, R.G. Olmstead and R.W. Scotland. 2004. Phylogenetic relationships among Strobilanthes S.L. (Acanthaceae): evidence from ITS and NR DNA, TRN L-F CP DNA, and morphology. American Journal of Botany 91(5): 724-735.

Carine, M.A., J.A. Alexander & R.W. Scotland. 2004. Species delimitation in the Strobilanthes  kunthiana group (Phlebophyllum sensu Bremekamp). Kew Bulletin 59: 1-25.

Moylan, E.C., Rudall, P.J. & R.W. Scotland. 2004. Comparative floral anatomy of Strobilanthinae (Acanthaceae), with particular reference to internal partitioning of the flower. Plant Systematics and Evolution 249: 77-98.

Wortley, A.H. & R.W. Scotland. 2004. Synonymy, sampling and seed plant numbers. Taxon 53(2): 478-480.

Scotland, R.W. & A.H. Wortley. 2003. How many species of seed plant are there? Taxon 52: 101 -104.

Scotland, R.W., C. Hughes, D. Bailey & A. Wortley. 2003. The Big Machine and the Much-Maligned Taxonomist. Systematics and Biodiversity 2: 139 -143.

Scotland, R.W., R.G. Olmstead & J.R. Bennett. 2003. Phylogeny reconstruction: the role of morphology. Systematic Biology 52(4): 539 – 548.

Wood, J.R. & R.W. Scotland. 2003. Strobilanthes: panicled species from East Asia. Kew Bulletin 58: 679 – 702.

Wood, J.R.I., J.R. Bennett & R.W. Scotland. 2003. Notes on Strobilanthes: the Sympagis group. Kew Bulletin 58: 131 – 173.

Wood, J.R.I. & R.W. Scotland. 2003. The 2-lipped species of Strobilanthes (Acanthaceae).Kew Bulletin 58: 83 – 129.

Bennett, J.R. & R.W. Scotland. 2003. A revision of Strobilanthes (Acanthaceae) in Java. Kew Bulletin 58: 1 – 82.

Moylan, E.C., R.T. Pennington & R.W. Scotland. 2002. Taxonomic account of Hemigraphis Nees (Strobilanthinae-Acanthaceae) from the Philipines. Kew Bulletin 57: 769 – 825.

Carine, M.A. & R.W. Scotland. 2002. Classification of Strobilanthinae (Acanthaceae): trying to classify the unclassifiable? Taxon 51: 259 – 279.

Wortley, A.H., J.R. Bennett & R.W. Scotland. 2002. Taxonomy and phylogeny reconstruction: two distinct research agendas in systematics. Edinburgh Journal of Botany 59(3): 335 – 349.

Fitter, D.W., D.J. Martin, M.J. Copley, R.W. Scotland & J.A. Langdale. 2002. GLK gene pairs regulate chloroplast development in diverse plant species. The Plant Journal 31(6): 713-727.

Carine, M.A., P. Jayasekera & R.W. Scotland. 2000. A new species of Strobilanthes Blume (Acanthaceae) from Sri Lanka. Kew Bulletin 55: 971 – 976.

Scotland, R.W. and M.A. Carine. 2000. Classification or phylogeny estimates? Cladistics 16: 411 – 419.

Scotland, R.W. & K. Vollesen. 2000. Classification of Acanthaceae. Kew Bulletin 55: 513 – 589.

Moylan, E.C. & R.W. Scotland. 2000. Hemigraphis neocaledonica Heine from New Caledonia is transferred to Brunoniella Bremek. (Acanthaceae). Kew Bulletin 55: 477 – 481.

Scotland, R.W. 2000. Are angiosperms firmly rooted? Taxon 49: 529 – 531.

Scotland, R.W. 2000. Taxic homology and three-taxon statement analysis. Systematic Biology 49(3): 480 – 500.

Carine, M.A. and R.W. Scotland. 2000. Taxonomy and biology of Stenosiphonium Nees (Acanthaceae). Botanical Journal of the Linnean Society 133: 101 – 128.

Steane, D.A., R.W. Scotland, D.J. Mabberley and R.G. Olmstead. 1999. Molecular Systematics of Clerodendrum (Lamiaceae). ITS sequences and total evidence. American Journal of Botany 86(1): 98 – 107.

Carine, M.A. and R.W. Scotland. 1999. Taxic and transformational homology: different ways of seeing. Cladistics 15: 121 – 129.

Carine, M.A. and R.W. Scotland. 1998. Pollen morphology of Strobilanthes Blume (Acanthaceae) from Southern India and Sri Lanka. Review of Paleobotany and Palynology 103: 143 – 165.

Scotland, R.W. 1998. One new and one re-discovered species of Strobilanthes Blume (Acanthaceae). Botanical Journal of the Linnean Society 128: 203 – 210.

Scotland, R.W. 1997. Parsimony neither maximizes congruence nor minimizes incongruence nor homoplasy. Taxon 46: 743 – 746.

Steane, D.A., R.W. Scotland, D.J. Mabberley, S.J. Wagstaff, P.A. Reeves and R.G. Olmstead. 1997. Phylogenetic relationships of Clerodendrum (Lamiaceae) inferred from chloroplast DNA. Systematic Botany 22: 229 – 243. 

Hawkins, J.A., C.E. Hughes and R.W. Scotland. 1997. Primary homology assessment, characters and character states. Cladistics 13: 275 – 283.

Scotland, R.W., J.A. Sweere, P.A. Reeves and R.G. Olmstead. 1995. Higher-level systematics of Acanthaceae determined by chloroplast DNA Sequences. American Journal of Botany 82:  266 – 275.

Scotland,R.W., Endress, P.K.& T.J. Lawrence. 1994.  Corolla ontogeny and aestivation in the Acanthaceae. Botanical Journal of the Linnean Society 114 (1): 49-65.

Scotland,R.W., 1993. Pollen morphology of Contortae (Acanthaceae). Botanical Journal of The Linnean Society 111 (4): 471-504.

Scotland R.W. & Williams D.M. 1993. Multistate characters and cladograms - when are 2 stamens more similar to 3 stamens than 4 - a reply to lipscomb. Cladistics 9 (3): 343-350.

Scotland, R.W. 1992. Pollen morphology and taxonomic characters in Acanthaceae. Systematic Botany 17 (2): 337-340.

Scotland, R.W. 1992. Pollen morphology of Andrographideae (Acanthaceae)Review of palaeobotany and palynology 72 (3-4): 229-243.

Scotland,R.W. 1992. Systematics, similarity and acanthaceae pollen morphologyBotanical Journal of The Linnean Society 109 (4): 529-541.

Williams, D.M., Scotland, R.W. & Blackmore S. 1990. Is there a direct ontogenetic criterion in systematics. Biological Journal of The Linnean Society 39 (2): 99-108.

Scotland, R.W.  Barnes, S.H. & S. Blackmore. 1990. Harmomegathy in the Acanthaceae - a Preliminary study of 3 pseudocolpate species using low-temperature scanning electron- microscopy. Grana 29 (1): 37-45.

Edited Books

1. La Guia “Darwin” de Las Flores de los Valles Bolivianos. (Field guide book edited by Darwin Initiative, 2005.

2. Homology and systematics, 2000: coding characters for phylogenetic analysis. (R.W. Scotland and R.T. Pennington eds). Taylor and Francis.

3. Models in Phylogeny Reconstruction, (R.W. Scotland, Siebert, D.J. and D.M. Williams, eds.) 1994. Clarendon press, Oxford.

4. Cladistics. (P. L. Forey, C. J. Humphries, I. L. Kitching, R. W. Scotland, D. J. Siebert, and D. M. Williams, eds.) 1992. Clarendon Press, Oxford. Also Published in Korean.

Book chapters

Scotland, R.W. 2013. Some observations on the homology of the daffodil corona, Chapter 12: 297-303 in Early Event in Monocot Evolution ed. P. Wilkin and S.J. Mayo. Cambridge University Press. The Systematics Association.

Scotland, R.W. 2000. Homology, coding and three-taxon statement analysis. In Homology and systematics: coding characters for phylogenetic analysis (R.W. Scotland and R.T. Pennington). Taylor and Francis.

Carine, M.A. and R.W. Scotland. 2000. 68 taxa and 32 characters: resolving species relationships using morphological data. In Pollen and spores: morphology and biology (C. M. Morton, M.M. Harley and S. Blackmore, eds), pp 365-384. Royal Botanic Garden Kew.

Scotland, R. W. 1992. In “Cladistics” (P. L. Forey, C. J. Humphries, I. L. Kitching, R. W. Scotland, D. J. Siebert, and D. M. Williams, Eds.), pp.. Clarendon Press, Oxford.

Scotland, R. W. 1992. Cladistic theory. In “Cladistics” (P. L. Forey, C. J. Humphries, I. L. Kitching, R. W. Scotland, D. J. Siebert, and D. M. Williams, Eds.), pp. 3–13. Clarendon Press, Oxford.

Scotland, R.W. 1991. A systematic analysis of pollen morphology of Acanthaceae genera with contorted corollas. In Pollen and Spores (S. Blackmore and S.H. Barnes eds), Systematics Association Special Volume No. 44,  pp. 269-289. Clarendon Press, Oxford


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