Phylogeny, Morphological Evolution, and Speciation of Endemic Brassicaceae Genera in the Cape Flora of Southern Africa Author(s): Klaus Mummenhoff, Ihsan A. Al-Shehbaz, Freek T. Bakker, H. Peter Linder, Andreas Mühlhausen Reviewed work(s): Source: Annals of the Missouri Botanical Garden, Vol. 92, No. 3 (Oct., 2005), pp. 400-424 Published by: Missouri Botanical Garden Press Stable URL: http://www.jstor.org/stable/40035479 . Accessed: 29/02/2012 04:58
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http://www.jstor.org PHYLOGENY, Klaus Mummenhoff,2 MORPHOLOGICAL Ihsan A. Al-Shehbaz,3 Freeh T. Bakkerf EVOLUTION,AND H. Peter hinderf SPECIATIONOF ENDEMIC and Andreas Miihlhausen6 BRASSICACEAEGENERA IN THE CAPE FLORA OF SOUTHERNAFRICA1
Abstract
Heliophila (ca. 73 spp.), the ditypic Cycloptychisand Thlaspeocarpa,and the monotypic Schlechteria, Silicularia, Brachycarpaea, and Chamira are endemic to the Cape region of South Africa, where they are the dominant genera of Brassicaceae. They may be regarded as the most diversified Brassicaceae lineage in every aspect of habit, leaf, flower, and fruit morphology.The characters used in the separation of these genera and their species, especially fruit type (silique vs. silicle), dehiscence (dehiscent vs. indehiscent), compression (latiseptate vs. angustiseptate),and cotyledonary type (spirolobal, diplecolobal, twice conduplicate), have been used extensively in the delimitation of tribes. The rela- tionship and taxonomic limits among these genera are unclear and controversial. The present ITS study demonstrates the monophyly of tribe Heliophileae, with Chamira as sister clade. The other five smaller genera above are nested within two of the three main lineages of Heliophila, to which they should be reduced to synonymy.The current study reveals parallel evolution of fruit characters often used heavily in the traditional classification schemes of the family. However, the arrangementof species into three main clades largely corresponds with the distribution of morphological characters (e.g., habit, leaf shape, seed structure, inflorescence type, and pres- ence/absence of basal appendages on the pedicels, petals, and staminal filaments) not adequately accounted for in previous studies. Estimation of divergence times of the main lineages of Heliophila is in agreement with recent esti- mations in other plant groups, all of which date the diversification against a backgroundof aridificationin the Pliocene and Pleistocene. Species of one main clade are perennial, microphyllous shrubs/subshrubstypically restricted to poor sandstone soils in the southwesternand western parts of the Cape Floristic Region of South Africa. Species of the other two clades are predominantlyannuals that grow in more arid regions of Namibia and Namaqualand,as well as in the above sandstone areas of the Cape Region. The adaptive significance of various floral structures is discussed in terms of their possible role in the rapid diversification within Heliophila. Key words: Brachycarpaea,Cape flora, Cape Floristic Region, Chamira, Cycloptychis,Heliophila, Heliophileae, ITS, phylogeny, radiation, Schlechteria, Silicularia, speciation, Thlaspeocarpa,trnL-F.
Seven genera of Brassicaceae, Heliophila (73 represent the dominant Brassicaceae. Although spp.), Cycloptychis(2 spp.), Schlechteria (1 sp.), Si- several classification systems (Table 1) have been licularia (1 sp.), Thlaspeocarpa (2 spp.), Brachy- proposed (e.g., Hayek, 1911; Schulz, 1936; Jan- carpaea (1 sp.), and Chamira (1 sp.), are endemic chen, 1942), the relationships among these genera to southern Africa (for authornames of these genera remain unresolved. In a recent re-evaluation of the and their species, see Table 1 and Appendix 1). group, Appel and Al-Shehbaz (1997) placed the Most species occur in the winter-rainfallarea of the first six genera in the tribe Heliophileae and re- western Cape Floristic Region (CFR), where they tained Chamira in the monotypic Chamireae.They
1 We are grateful to the directors, curators, and collectors of the institutions that provided the plant material. We thank Ulrike Coja for technical assistance, Andreas Franzke for fruitful discussions, and Adelaide Stork, Ashley Nicholas, and two anonymous reviewers for constructive criticisms that helped improve the final draft. 2 Departmentof Botany, Faculty of Biology/Chemistry,University of Osnabrtick,Barbarastrasse 11, 49069 Osnabriick, [email protected]. 3 Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri, U.S.A. 63166-0299. 4 [email protected]. National Herbarium Nederland, Wageningen branch & Biosystematics Group, Wageningen University, Generaal Foulkesweg 37, 6703 BL Wageningen,The Netherlands, [email protected]. 5 Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008, Switzerland, plin- [email protected]. 6 Departmentof Botany,Faculty of Biology/Chemistry,University of Osnabriick,Barbarastrasse 11, 49069 Osnabriick, [email protected]. Ann. Missouri Bot. Gard. 92: 400-424. Published on 10 October 2005. Volume 92, Number 3 Mummenhoff et al. 401 2005 Brassicaceae In Cape Flora
0^ C^ & 02 02 QJ characterized the by dipleco- 2 cd cd cd cd cd cd Heliophileae having lobal cotyledons (elongated and twice transversely folded). This uncommon cotyledonary type is also ill " ' j!!!!!l