BACKGROUND: The southern African Oxalis radiation is extremely morphologically variable. Despite recent progress in the phylogenetics of the genus, there are few morphological synapomorphies supporting DNA-based clades. Leaflet anatomy can provide an understudied and potentially valuable source of information on the evolutionary history and systematics of this lineage. Fifty-nine leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades. RESULTS: A combination of 6 leaflet anatomical traits (stomatal position, adaxial epidermal cells, abaxial epidermal cells, mesophyll, sheath around vascular tissue, degree of leaflet conduplication) clearly support various clades defined by previous DNA-based phylogenetic work. Other, mostly continuous leaflet anatomical traits were highly variable and showed less phylogenetic pattern. CONCLUSIONS: Major and unexpected findings include the transition from ancestral hypostomatic leaflets to adaxially-located stomata in the vast majority of southern African Oxalis, the loss of semi-swollen AB epidermal cells and the gain of swollen adaxial and abaxial epidermal cells in selected clades, and multiple changes from ancestral bifacial mesophyll to isobilateral or homogenous mesophyll types. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region and provide a basis for future hypotheses regarding its radiation.

Department Conservation Ecology and Entomology Stellenbosch University Private Bag X1 Matieland 7602 South Africa

Department of Botany and Zoology University of Stellenbosch Private Bag X1 Matieland 7602 South Africa

Institute of Botany Academy of Sciences Průhonice CZ 252 43 Czech Republic

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Carlquist S. Comparative plant anatomy: A guide to taxonomic and evolutionary applications of anatomical data in angiosperms. New York: Rinehart Winston; 1961.

Radford AE, Dickison WC, Massey JR, Bell CR. Vascular Plant Systematics. New York: Harper and Row Publishers; 1974.

Metcalfe CR. Anatomy of the dicotelydons. 2nd ed. vol. 1: Systematic anatomy of leaf and stem, with a brief history of the subject. Oxford: Oxford Science; 1979.

Stuessy TF. Plant taxonomy. New York: Columbia University Press; 1990.

Judd WS, Campbell CS, Kellogg EA, Stevens PF, Donoghue MJ. Plant systematics: a phylogenetic approach. 3. Massachusetts: Sinauer Associates INC.; 2008.

Olmstead RG. Whatever happened to the Scrophulariaceae. Fremontia. 2002;30:13–22.

Xia Z, Wang Y, Smith JF. Familial placement and relations of Rehmannia and Triaenophora (Scrophulariaceae S.L.) inferred from five gene regions. Am J Bot. 2009;96:519–530. doi: 10.3732/ajb.0800195. PubMed DOI

Salter TM. The genus Oxalis in South Africa: a taxonomic revision. J South Afr Bot. 1944;1:1–355.

Lourteig A. Oxalis L. subgenera Monoxalis (Small) Lourteig, Oxalis Trifidus Lourteig. Bradea, 2000;201–629.

Chant SR. Oxalidaceae. In: Heywood VH, editor. Flowering Plants of the world. Oxford: Oxford University Press; 1978.

Takhtajan A. Floristic regions of the world. Berkeley: University of California Press; 1997.

Leistner AO. Seed plants of southern Africa: families and genera. Pretoria: Strelitza; 2000. p. 10.

Denton MD. A monograph of Oxalis Section Ionoxalis (Oxalidaceae) in North America. East Lansing: Publications of the Museum, Michigan State University Biological Series; 1973.

Oberlander KC, Dreyer LL, Esler KJ. Biogeography of Oxalis (Oxalidaceae) in South Africa: a preliminary study. Bothalia. 2002;32:97–100. doi: 10.4102/abc.v32i1.472. DOI

Oliver EGH. Oxalidaceae: a new species of Oxalis from the Western Cape. Bothalia. 1993;23:72–74.

Manning J, Goldblatt P. Plants of the greater cape floristic region 1: the core cape flora. Pretoria: Strelitzia; 2012. p. 29.

Born J, Linder HP, Desmet P. The Greater Cape Floristic Region. J Biogeography. 2006;1–16. doi:10.1111/j.1365-2699.2006.01595.x

Gebregziabher AK. Systematic significance of bulb morphology of the southern African members of Oxalis L. (Oxalidaceae). Stellenbosch University: Master’s thesis; 2004.

Oberlander KC, Dreyer LL, Bellstedt DU. Molecular phylogenetics and origins of southern African Oxalis. Taxon. 2011;60(6):1667–1677.

Knuth RGP. Oxalidaceae. In Engler A, editor. Das Pflanzenreich 95 IV. Leipzig; 1930.

Dreyer LL. A palynological review of Oxalis (Oxalidaceae) in southern Africa. University of Pretoria: PhD; 1996

Oberlander KC. Molecular systematic study of southern African Oxalis (Oxalidaceae). Stellenbosch University: PhD thesis; 2009.

Oberlander KC, Dreyer LL, Bellstedt DU, Reeves G. Congruence if trnL-F and palynological data sets in the southern African Oxalis L section Angustatae subsection Lineares. Taxon. 2004;53:977–985. doi: 10.2307/4135564. DOI

Gardner AG, Vaio M, Guerra M, Emshwiller E. Diversification of the American bulb-bearing Oxalis (Oxalidaceae): Dispersal to North America and modification of the tristylous breeding system. Am J Bot. 2012;99:152–164. doi: 10.3732/ajb.1100152. PubMed DOI

Vaio M, Gardner A, Emshwiller E, Guerra M. Molecular phylogeny and chromosome evolution among the creeping herbaceous Oxalis species of sections Corniculatae and Ripariae (Oxalidaceae) Mol Phylogenet Evol. 2013;68:199–211. doi: 10.1016/j.ympev.2013.03.019. PubMed DOI

Weller SG. Evolutionary modifications of tristylous breeding systems. In: Barrett SCH, editor. Evolution and function of heterostyly. Berlin: Springer-Verslag; 1992.

Weller SG, Doninguez CA, Molina-Freaner FE, Fornoni J, LeBuhn G. The evolution of distyly in populations of Oxalis alpina (Oxalidaceae) in the Sky Islands of the Sonoran Desert. Am J Bot. 2007;94:972–985. doi: 10.3732/ajb.94.6.972. PubMed DOI

Weber JJ, Weller SG, Sakai AK, Tsyusko OV, Glenn TC, Molina-Freaner FE, Dominguez CA, Fornoni M, Tran J, Nguyen N, Tran L, Joice G, Harding E. The role of inbreeding depression and mating sysytem in the evolution of heterostyly. Evolution. 2013;67:2209–2322. doi: 10.1111/evo.12123. PubMed DOI

Zietsman J, Dreyer LL, Esler KJ. Reproductive biology and ecology of selected rare and endangered Oxalis L. (Oxalidaceae) plant species. Biol Conserv. 2008;141:1475–1483. doi: 10.1016/j.biocon.2008.03.017. DOI

Turketti SS, Esler KJ, Dreyer LL. Three-dimensional reciprocity: A new form of tristyly in South African Oxalis (Oxalidaceae) species and its implications for reproduction. S Afr J Bot. 2012;78:195–202. doi: 10.1016/j.sajb.2011.06.014. DOI

de Jager ML, Dreyer LL, Ellis AG. Do pollinators influence the assembly of flower colours within plant communities? Oecologia. 2011;166:543–553. doi: 10.1007/s00442-010-1879-7. PubMed DOI

Dreyer LL, Esler KJ, Zietsman J. Flowering phenology of South African Oxalis -possible indicator of climate change? S Afr J Bot. 2006;72:150–156. doi: 10.1016/j.sajb.2005.06.009. DOI

Rosenfeldt S, Beatriz GG. Ubisch bodies and pollen ontogeny in Oxalis articulate Savigny. Biocell. 2005;29:271–278. PubMed

De Azkue D. Chromosome diversity of South American Oxalis (Oxalidaceae) Bot J Linn Soc. 2008;132:143–152. doi: 10.1111/j.1095-8339.2000.tb01210.x. DOI

Matthews ML, Endress PK. Comparative floral structure and systematics in Oxalidales Oxalidaceae, Connaraceae, Brunelliaceae, Cephalotaceae, Cunoniaceae, Elaeocarpaceae, Tremandraceae) Bot J Linn Soc. 2002;140:321–381. doi: 10.1046/j.1095-8339.2002.00105.x. DOI

Robb S. Oxalis latifolia Kunth. New Phytol. 1963;62:75–79. doi: 10.1111/j.1469-8137.1963.tb06314.x. DOI

Levy F, Moore D. Population variations of leaflets sleep movements in Oxalis grandis (Oxalidaceae) Am J Bot. 1993;80:1482–1493. doi: 10.2307/2445678. DOI

Pedersen M, Johnsson A, Maehle J, Dalokken R. Short period leaf movements in Oxalis regnelii. Physiol Plant. 2006;89:277–284. doi: 10.1111/j.1399-3054.1993.tb00154.x. DOI

Lopez A, Panseri AF, Urtubey E. Revision of genus Oxalis L. section Palmatifoliae (Oxalidaceae) Phytotaxa. 2003;138:1–14. doi: 10.11646/phytotaxa.138.1.1. DOI

Benitez C, Ferrarotto M. Morfología de la epidermis foliar en dos grupos de Solanum sección Geminata (Solanaceae) Caldasia. 2009;31(1):31–40.

Moon HK, Hong SP, Smets E, Huysmans S. Phylogenetic significance of leaf micromorphology and anatomy in the tribe Mentheae (Nepetoideae: Lamiaceae) Bot J Linn Soc. 2009;160(2):211–231. doi: 10.1111/j.1095-8339.2009.00979.x. DOI

Soh WK, Parnell J. Comparative leaf anatomy and phylogeny of Syzygium Gaertn. Plant Syst Evol. 2011;297(2):1–32. doi: 10.1007/s00606-011-0495-2. DOI

Storey M. BioImages. United Kingdom: The Virtual Field-Guide; 2006.

Wood A. Class-Book of Botany. USA and Canada: A.S Barnes and Co; 1874.

Haberlandt G. Physiological Plant Anatomy. Dordrecht: Kluver Academic Publishers; 1914.

Wiggins IL, Porter DM. Flora of the Galapagos Islands. Stanford: Stanford University Press; 1971.

Steudle E. Planta of Oxalis carnosa Molina. Planta. 1983;159(1):38–45. doi: 10.1007/BF00998812. PubMed DOI

Eiten G. Taxonomy and regional variation of Oxalis section Corniculatae. Introduction, keys and synopsis of species. Am Midland Nat J. 1963;69:257–309. doi: 10.2307/2422912. DOI

dos Reis AE, Alvim MN. Anatomia foliar comparada de três espécies do gênero Oxalis. Belo Horizonte MG. 2013;3(6):59–72.

Freire SE, Arambarri ANAM, Bayón ND, Sancho G, Urtubey E, Monti C, Novoa MC, Colares MN. Epidermal characteristics of toxic plants for cattle from the Salado river basin (Buenos Aires, Argentina) Bol Soc Argent Bot. 2005;40(3-4):241–281.

Toma C, Gostin I, Ivanescu L. Histo-anatomical details of the Oxalis corniculata L. Biologie vegetala. 2007;5-10.

De Villiers MJ. A systematic revision of Oxalis L. section Crassulae T.M. Salter (Oxalidaceae). Stellenboch University: Master’s thesis; 2001.

Jones SB, Luchsinger AE. Plant Systematics. 2nd ed. New York: McGraw-Hill Book Company; 1987.

Dellagreca M, Previtera L, Zarrelli A. A new aromatic component from Oxalis pes-caprae. Nat Prod Rev. 2015;24(10):958–961. doi: 10.1080/14786410902809286. PubMed DOI

Šircelj H, Mikulic-Petkovsek M, Batic F. Antioxidants in spring leaves of Oxalis acetosella L. Food Chem. 2010;123:351–357. doi: 10.1016/j.foodchem.2010.04.042. DOI

Abhilash PA, Nilasha A, Pratapan A, Suresh VN, Lizocherian O, Sunitha TK, Raghu KG. Cardio protective effects of aqueous extract of Oxalis corniculata in experimental myocardial infarction. Experimental and Toxicological Pathway. 2011;63:535–540. doi: 10.1016/j.etp.2010.04.004. PubMed DOI

Willmer C, Fricker M. Stomata. 2nd edition. London: Chapman and Hall; 1996.

Johansen DA. Plant Microtechnique. New York: McGraw-Hill; 1944.

Abràmoff MD, Magalhães PJ, Ram SJ. Image processing with ImageJ. Biophoton Int. 2004;11(7):36–41.

Drummond AJ, Suchard MA, Xie D, Rambaut A. Bayesian Phylogenetics with BEAUti and the BEAST 1.7. Mol Biol Evol. 2012;29(8):1969–1973. doi: 10.1093/molbev/mss075. PubMed DOI PMC

R-Core-Team . R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing; 2014.

Paradis E, Claude J, Strimmer K. APE: analyses of phylogenetics and evolution in R language. Bioinformatics. 2004;20:289–290. doi: 10.1093/bioinformatics/btg412. PubMed DOI

Harmon LJ, Weir JT, Brock CD, Glor RE, Challenger W. GEIGER: investigating evolutionary radiations. Bioinformatics. 2008;24:129–131. doi: 10.1093/bioinformatics/btm538. PubMed DOI

Bozdogan H. Model selection and Akaike’s Information Criterion (AIC): the general theory and its analytical extensions. Psychometrika. 1987;52:435–470. doi: 10.1007/BF02294361. DOI

Posada D, Buckley TR. Model Selection and Model Averaging in Phylogenetics: Advantages of Akaike Information Criterion and Bayesian Approaches Over Likelihood Ratio Tests. Syst Biol. 2004;53:793–808. doi: 10.1080/10635150490522304. PubMed DOI

Revell LJ. Phytools: An R package for phylogenetic comparative biology (and other things) Methods Ecol Evol. 2012;3:217–223. doi: 10.1111/j.2041-210X.2011.00169.x. DOI

Esau K. Plant Anatomy. New York: Wiley; 1953.

Schluter D, Price T, Mooers AO, Ludwig D. Likelihood of ancestor states in adaptive radiation. Int J Org Evol. 1997;51(6):1699–1711. doi: 10.2307/2410994. PubMed DOI

Watson RW. The effect of cuticular hardening on the form of epidermal cells. New Phytol. 1942;41(4):223–229. doi: 10.1111/j.1469-8137.1942.tb07075.x. DOI

Esau K. Plant Anatomy. New York, London, Sydney: John Wiley and Sons Inc; 1965.

Kürschner WM. The anatomical diversity of recent and fossil leaves of the durmast oak (Quercus petraea Lieblein/Q. pseudocastanea Goeppert) - Implications for their use as biosensors of palaeoatmospheric CO2 levels. Rev Palaeobot Palynol. 1997;96(1-2):1–30. doi: 10.1016/S0034-6667(96)00051-6. DOI

Metcalfe CR, Chalk L. Anatomy of the dicotylrdons, vol 2. 1950.

Heibl C. Studies on the systematic, evolution, and biogeography of Oxalis sections Caesiae, Carnosae, and Giganteae, endemic to the Atacama Desert of northern Chile. Ludgig Maximilian University of Munich: PhD thesis; 2005.

Poulson ME, Vogelmann TC. Epidermal focussing and effects upon photosynthetic light-harvesting in leaves of Oxalis. Plant Cell Environ. 1990;13(8):803–811. doi: 10.1111/j.1365-3040.1990.tb01096.x. DOI

Myers DA, Vogelmann TC, Bornmann JF. Epidermal focussing and effects on light utilization in Oxalis acetocella. Physiol Plant. 1994;91(4):651–656. doi: 10.1111/j.1399-3054.1994.tb03001.x. DOI

Vogelmann TC, Bornmann JF, Yates DJ. Focussing of light by leaf epidermal cells. Physiol Plant. 1996;98(1):43–56. doi: 10.1111/j.1399-3054.1996.tb00674.x. DOI

Parkhurst DF. The adaptive significance of stomatal occurrence on one or both surfaces of leaves. J Ecol. 1978;66:367–383. doi: 10.2307/2259142. DOI

Yates MJ, Verboom GA, Rebelo AG, Cramer MD. Ecophysiological significance of leaf size variation in Proteaceae from the Cape Floristic Region. Funct Ecol. 2010;24:485–492. doi: 10.1111/j.1365-2435.2009.01678.x. DOI

Gutschick VP. Photosynthesis model for C3 leaves incorporating CO2 transport, propagation of radiation, and biochemistry, 2. Ecological and agricultural utility. Photosynthetica. 1984;18:569–595.

Muir CD. Selection constrains phenotypic evolution in a functionally important plant trait. University of British Columbia: PhD thesis; 2015.

Bohley K, Joos O, Hartmann H, Sage R, Liede-schumann S, Kadereit G. Phylogeny of Sesuvioideae (Aizoaceae). Biogeography, leaf anatomy and the evolution of C4 photosynthesis. Perspect Plant Ecol Evol Syst. 2015;17(2):116–130. doi: 10.1016/j.ppees.2014.12.003. DOI

Mashayekhi S, Columbus JT. Evolution of the leaf blade anatomy in Allium (Amayllidaceae) subgenus Amerallium with a focus on the North American species. Am J Bot. 2014;101(1):63–85. doi: 10.3732/ajb.1300053. PubMed DOI

Goebel K. Organographie der Pflanzen. 1898;1–158