Original Paper Isozymes, Speciation and Evolution in the Polyploid Complex Cochlearia L. (Brassicaceae) M. Koch, Marion Huthmann, and H. Hurka Department of Botany, University of Osnabruck, 0-49079 Osnabruck, Germany Received: February 9, 1998; Accepted: August4,1998 411 Abstract: Within the genus Coch/earia l. sect. Coch/earia three isozyme systems (aspartate aminotransferase, leucine amino- peptidase and phosphoglucomutase) have been analysed at the populational level for eleven species with different ploidy levels. Nine loci complexes were resolved with a total of 33 al- leles from 89 populations. In general, polypiaids displayed higher numbers of alleles per species and per population. A notable exception is diploid C. pyrenaiea with as many alleles as some polyploids. Data sup- port: (1) the origin of tetraploid C.officinalis from C. pyrenaiea s.l., particularly from C. aestuaria; (2) the atuopolyploid origin of octoploid C. anglica from C. offieinalis; (3) the allopolyploid origin of hexaploid inland taxa C. p%niea, C. tatrae and C. bavar- iea via hybridization between C. pyrenaiea and C. officinatis; (4) a putative allopolyploid origin of hexaploid coastal species C.da- niea by hybridization between C. pyrenaiea s./. and C. officinalis accompanied by a shift in chromosome complement. Ascenar- io summarizing our present understanding of the evolution within Coch/earia sect. Coch/earia is presented. Key words: Coch/earia, Brassicaceae, isozyme, polyploidization, evolution. Introduction In Western Europe the genus Coch/earia 1. is divided into two sections, G/aucocochlearia and Cochlearia. Section Glaucoco- ch/earia O. E. Schulz is distributed in south-west Europe and includes a few annual, highly polyploid species (Koch et al., 1996; Koch et al., 1998a; VOg!, 1993). The members of section Cochlearia (= Eucochlearia Prantl) are distributed along the coasts from Portugal to Norway and in mountains north of the 43th parallel up to 2300 m a.s.l. Arctic-circumpolar taxa of section Cochlearia are: Cgroenlandica L. in arctic continental Europe, Greenland and Iceland, including Cfenestrata R. Br. and C arctica Schlecht (see Love and LOve, 1975); C tridactylitis Banks in northern America; C oblongifolia DC. in Japan. The arctic-circumpolar taxa are diploid and are well separated from the remaining diploids by the chromosome number of 2n =14 instead of 2n= 12.ln Iceland, however, there are two diploid cytotypes, 2 n = 12 and 2 n = 14, both referred to as Cgroen/and- ica (Koch et al., 1996; Nordal and Laane,1990). Within the n = 6 Bot. Acta 111 (1998)411-425 © Georg Thieme Verlag Stuttgart· New York series there are 15 species according to the generic revision of Pobedimova (1969, 1970). Pobedimova's treatments appear to be artificial, and are characterised by taxonomical splitting (Koch et al., 1998a). We followed the more traditional concept of Vogt (1985) and Nordal (1988) for European taxa. Diploid taxa are C aestuaria (Lloyd) Heywood along the coasts of northern Spain and southern France, and Cpyrenaica 5./. (syn. c. alpina Barb.) at inland localities in continental Europe and Britain, rarely at coastal sites in Scotland (Nordal, 1988). The c.pyrenaica species complex includes endemic taxa such as C. macrorrhiza (Schur.) Pobed. (Austria, extinct in the wild) and C excelsa Zahlbr. confined to high elevations in the eastern Alps of Austria. The tetraploid C offidnalis 1. is distributed along the northern coasts of Europe. In Scandinavia, this taxon shows a broad range of ecological and morphological differentiation and is divided into different ecotypes and subspecies (Nordal and Stabbetorp, 1990). Inland C. offidnali5 is known from heavy metal contaminated soils in Britain. The octoploid C. anglica L. is distributed from the coasts of northern France to southern Sweden, and is clearly separated from the hexaploid C danica L. by the morphological and ecological characters. In contrast to all other taxa of section Cochlearia, C. danica is an annual and ephemeral pioneer of the coastal sand dune vegetation (Koch, 1996; Koch, 1997). Highly polyploid inland taxa are Cpolonica Frohl, and C tatrae Borb. of Poland and Slovakia, respectively, and C bavarica Vogt of Bavaria. Much is known about variation in cytology, morphology and ecology (Gill, 1971b; Gill et al., 1978). Evolutionary processes, still in progress, are demonstrated by poorly established fertility barriers and numerous interspecific hybrids (Crane and Gairdner, 1923; Davis, 1976; Fearn, 1977; Focke, 1916; Gadella, 1983; Garve, 1994; Gill,1971a; Gill,1975; Serensen and West- ergard, 1948), and present day distribution of Cochlearia might reflect a post-glacial history. The aim of this work is to analyse speciation and differentiation at the molecular level in Cochlearia section Cochlearia. A first molecular survey using RAPDs and chloroplast DNA restriction site variation (Koch et al.,1996) revealed novel insights into reticulation and system- atic relationships, especially within C. offidnalis, C. anglica and C. danica and indicated a large phylogenetic distance between sect. Glaucococh/earia and sect. Coch/earia. An evolutionary analysis above the sectional level within subtribe Cochlear- iinae has been performed using nuclear and plastidic DNA sequences (Koch et aI., 1998a). Phylogenetic relationships among several taxa within sect. Cochlea ria remained unclear. In the present study we use isozyme analyses to study