S.Afr.J. Bot., 1989,55(3): 321-331 321 What is primitive in Mesembryanthemaceae? An analysis of evolutionary polarity of character states V. Bittrich* and M. Struck Institut fUr Allgemeine Botanik und Botanischer Garten der Universitat Hamburg, Ohnhorststr. 18, D-2000 Hamburg 52, West Germany Accepted 16 November 1988 Characters of the family Mesembryanthemaceae are investigated with respect to their state (primitive or derived) within this family. Out-group comparison with the closely related family Aizoaceae s.str. (excl. Mesembryanthemaceae) is used mainly, along with some other criteria. A tabulated survey of the characters discussed is provided. By combination of all characters considered as primitive, a morphotype (,hypothetical ancestor') of the Mesembryanthemaceae can be constructed. It is shown that no extant taxon possesses all features of this morphotype, but that all have acquired a number of derived characters. The possibility of the meronectary being a further synapomorphy of the family is discussed. A new synapomorphy for the subfamily Mesembryanthemoideae, namely the absence of expanding sheets on the valves of the hygrochastic capsule, is provided. The fundamental splitting of the Mesembryanthemaceae in two monophyletic subfamilies (Mesembryanthemoideae and Ruschioideae) is further supported by the results. Kenmerke van die familie Mesembryanthemaceae word, met betrekking tot hul toestand (primitief of afgelei) binne die familie, ondersoek. Buitegroep-vergelyking met die naverwante familie Aizoaceae s. str. (wat die Mesembryanthemaceae uitsluit) word hoofsaaklik, saam met ander kriteriums gebruik. 'n Getabuleerde oorsig van die kenmerke onder bespreking, word voorsien. Deur middel van 'n kombinasie van al die kenmerke wat as primitief beskou word, kan 'n morfotipe (hipotetiese voorouer) van die Mesembryanthemaceae gekonstrueer word. Daar word aangetoon dat geen lewende takson oor al die kenmerke van die morfotipe beskik nie, maar dat almal 'n aantal afgeleide kenmerke ontwikkel het. Die moontlikheid van meronektarie as 'n verdere sinapomorfiese kenmerk van die familie word bespreek. 'n Nuwe sinapomorfie van die subfamilie Mesembryanthemoideae, naamlik die afwesigheid van die uitspreidende plate van die higrochastiese kapsule, word voorsien. Die fundamentele verdeling van die Mesembryanthemaceae in twee monofiletiese subfamilies (Mesembryanthemoideae en Ruschioideae) word verder deur die resultate ondersteun. Keywords: Aizoaceae, character states, Mesembryanthemaceae, morphotype, synapomorphies *To whom correspondence should be addressed Introduction Aizoon L., differ least from the Mesembryanthemaceae The Mesembryanthemaceae (130 genera with about and show the smallest patristic distance. This led Dinter 1 000 species), a family belonging to the Caryophyllales (1935) erroneously to regard Aizoanthemum as a 'trans­ (Centrospermae) are native to the deserts and semi­ itional taxon' between Aizoaceae s.stt. (excl. Mesem­ deserts of southern Africa. They form a natural mono­ bryanthemaceae) and Mesembryanthemaceae. phyletic group comprising two subfamilies Mesembryan­ The most important synapomorphy of the entire Aizo­ themoideae (= Aptenioideae) and Ruschioideae (incl. aceae S.str. is the epidermal bladder-cell idioblasts Caryotophoroideae and Hymenogynoideae; Bittrich (much enlarged cells with water-storing function). 1986; Bittrich & Hartmann 1988). As discussed Further evolution into homogeneous, more xeromorphic elsewhere (Bittrich 1986; Bittrich & Hartmann 1988) epidermis-types is well documented (e.g. Ihlenfeldt & these subfamilies are closely related to the Aizooideae, Hartmann 1982). Other possible synapomorphies such Sesuvioideae and Tetragonioideae. All five subfamilies as perigynous flowers, and hygrochastic capsules are form a monophyletic group and could be combined discussed elsewhere (see Bittrich 1986; Bittrich & under the name Aizoaceae S.str. (s.str. = excl. Mollugin­ Hartmann 1988). aceae). The composition of the Aizoaceae S.str. is shown The Mesembryanthemaceae are defined by the follow­ in Table 1. We would like to emphasize, however, that it ing synapomorphies: (petaloid) staminodes, the absence is of major importance to characterize monophyletic of a superior ovary, and possibly the well-formed valve groups, whereas their ranking remains open to some wings of the fruit (see below). The Aizoaceae S.str. subjectivity (unless the classification is strictly (excl. Mesembryanthemaceae) are characterized by the c1adistical). For methodological reasons, in the follow­ chromosome base number x=8 (7) (Mesembryanthema­ ing, the Mesembryanthemaceae and Aizoaceae S.str. ceae x=9) and the tepals, which are petaloid on the inner (excl. Mesembryanthemaceae) will be treated as (upper) side. These characters could be regarded as separate families (see Table 1). synapomorphies (Bittrich & Hartmann 1988), but the Undoubtedly, the genera of the Aizooideae, espec­ relationship between the subfamilies is not satisfactorily ially the genera Aizoanthemum Dinter ex Friedrich and settled (see below). All Aizoaceae S.str. produce 322 S.-Afr.Tydskr. Plantk., 1989,55(3) Table 1 Composition of the Aizoaceae s.str. (for further discussion see Bittrich & Hartmann 1988) Aizoaceae S.str. (= excl. Molluginaceae) Aptenioideae = Mesembryanthemoideae Mesembryanthemaceae Ruschioideae ] Aizooideae Aizoaceae S.str. (excl. Tetragonioideae Mesembryanthemaceae) Sesuvioideae J betalains as flower pigments (as do most centrospermous primitive. families). Muller (1909) already found differences in the As regards the relationship of the three subfamilies of type of calcium oxalate crystals: within the Mesembry­ the Aizoaceae s.str. (excl. Mesembryanthemaceae) two anthemaceae, raphid bundles occur, whereas druses are hypotheses should be considered. Either all three sub­ found within the Aizoaceae S.str. (excl. Mesem­ families form a single monophyletic group as suggested bryanthemaceae). As the question of the closest relative by the synapomorphies mentioned above (Bittrich 1986; of these families within the Centrosperms (i .e. the sister Bittrich & Hartmann 1988), or a monophyletic group group) is still not settled (contra Rodman et al. 1984; consisting of Aizooideae and Tetragonioideae (Hof­ Levin 1985; Bittrich & Hartmann 1988) one cannot yet mann 1973; Bittrich in press) represents the sister group decide which of these crystal types has to be considered of the Mesembryanthemaceae as suggested by the capsule type and the epicuticula of the seed coat (see below). In this case the Sesuvioideae would be the sister Tetragonioideae Sesuvioideae Aizooideae Mesembryanthemaceae group of the rest of the Aizoaceae S.str. (see Figure 1). This problem as well as the relationship within the monophyletic group Aizooideae/Tetragonioideae will be discussed at length elsewhere (Bittrich in press). So far, the question of primitive characters of the Mesembryanthemaceae has only rarely been discussed (Ihlenfeldt 1960; Bittrich 1986 for Mesembryanthe­ moideae). Therefore, this paper intends to amplify the knowledge in this field, which is essential for a further analysis of the phylogeny of this family. New results are included. A A number of characters will be examined with respect to their evolutionary polarity. Based on that survey, a list of the characters with their putative primitive (ancestral) and advanced (derived) states is given. By the combination of the primitive features the morpho­ type (sometimes called 'hypothetical ancestor', Nelson 1972; for discussion of terms see Hull 1979) of the Mesembryanthemaceae can be constructed. Tetragonioideae Sesuvioideae Aizooideae Mesembryanthemaceae Materials and Methods The basis of the present investigations is comprehensive data extracted from the available literature and other sources as well as from our studies of herbarium speci­ mens and living plants from the collection of the Mesem­ bryanthemaceae study group in Hamburg (West Germany) under the direction of Prof. H-D. Ihlenfeldt. Methods and criteria to determine primitive character B states have been discussed extensively in a number of recent publications (e.g. Crisci & Stuessy 1980; Humphries & Funk 1984; Stevens 1980; Wiley 1980). Figure 1 Possible sister-group relationships in Aizoaceae For this determination, 'the out-group criterion is the S.str. inc\. Mesembryanthemaceae. A. Mesembryanthemaceae main criterion used by phylogeneticists' as Wiley (1980) are the sister-group to the rest of the Aizoaceae S.str. B. put it. The application of this criterion has been Mesembryanthemaceae and Aizooideaeffetragonioideae are thoroughly examined (e.g. Donoghue & Cantino 1984; sister-groups. Maddison et al. 1984; Wiley 1981). The most useful out- S.Afr.J. Bot., 1989, 55(3) 323 group for character comparison and evaluation is the suggests that herbaceous growth forms are primitive sister-group of the taxon under investigation. As within this family. Furthermore: most of the taxa mentioned above, the sister-group of the Mesembryan­ showing several other primitive characters within both themaceae is not defined unequivocally. Therefore, in subfamilies of Mesembryanthemaceae (Mesembryanthe­ cases with different character states in the two possible mum L., Cleretum, Dorotheanthus) are more or less sister-groups, an out-group comparison necessarily must herbaceous. Hence, the application of the criterion of lead to uncertain results. When an out-group character correlation gives further evidence for the comparison cannot be applied, additional criteria