PHYLOGENY ANDSPECIATION IN LAPEIROUSIASUBGENUS LAPEIROUSIA(IRIDACEAE: IXIOIDEAE)1Peter Goldblatt2 andJohn C. Manning"A BSTRACT A cladistic analysis of southern African subgenus Laipeirousia. one of two subgenera of the exclusively African genusLapeirousia, yielded four equally parsimonious trees, one of which is identical with the strict consensus tree. Charactersused in the analysis included growth form, corm morphology, a range of floral characters, and capsule and seed features,not before known to vary significantly in this genus. The analysis suggested some surprising evolutionary changes.Notable among these is an apparent reversal of perianth tube length from extremely long to short, a shift correspondingto a change from pollination by long-tongued flies and sphinx moths to pollination by becs and noctuid moths. Anotherunusual change is a shift in floral organization from zygomorphy to actinomorphy correlated with an acaulescent growthform. The reconstructed phylogeny is used here to assess character evolution and patterns of speciation by comparisonof species in terminal clades in the cladograms. The resulting comparisons suggest that speciation in the subgenus iseither allopatric or the resuit of microgeographic differentiation and ecological diversification stimulated by edaphicdiversity. Despite the variety of floral forms and pollination syndromes in the subgenus there is no evidence of sympatricor pollinator-driven speciation. Prepollination reproductive isolation appears to be achieved by shifts in pollinationsyndromes between sphinx moths, two guilds of long-tongued flies, and becs. The remarkable floral divergence that hasresulted appears to be a consequence of selection for repeated entry into preexisting pollination guilds. The mostimportant of these pollination guilds are two long-tongued fly guilds in which either Prosoeca (Nemestrinidae) orMoegistorhynrhus (Nemestrinidae) and Philoliche (Tabanidae) are pollinators. These two guilds are also likely to havebeen important in promoting speciation in other genera and families in the southern African flora. The flora of southern Africa is rich and unusuallydiverse for an area falling predominantly in tem-perate latitudes (Goldblatt, 1978). Some 20,400species of native vascular plants are currently rec-ognized in the region (Arnold & de Wet, 1993), ofwhich about 80% are endemic (Goldblatt, 1978).The major factors proposed to account for the spe-cies richness are climatic, edaphic,. and topograph-ie diversity and a history of paleoclimatic changein the late Tertiary (Goldblatt, 1978). Althoughthese factors may permit the existence of largenumbers of species, they do not indicate the modesof speciation that have led to this diversity. Onemethod of inferring modes of speciation is by com-paring biological attributes of closely related, andby extension evolutionarily recent, sister species.Differences in biology between such species givean indication of the factors that led to speciation.Cladistic analysis is a critical method for identify-ing sister species. A detailed phylogenetic hypoth-esis such as a cladogram makes it possible to tracebackwards in time the series of evolutionary eventsthat gave rise to the modern taxonomic distributionof ecological features even in the absence of fossilinformation (Armbruster, 1993). This in turn makesit possible to develop specific hypotheses on theevolution of species diversity (Manning & Linder,1992). The tropical and southern African genus Lapei-rousia Pourret comprises some 40 species segre-gated in two subgenera each with two sections(Goldblatt & Manning, 1990, 1992, 1994). Subge-nus Lapeirousia (21 species) is centered in coastaland near interior southwestern Africa. This is asemiarid region of low to moderate winter rainfallanrd extreme summer drought. Two species arewidespread in the southwestern and southern partsof Western Cape Province, South Africa, and a fur-ther two occur in tropical Africa (Goldblatt, 1990b).Subgenus Paniculata (19 species) comprises thelargely tropical African section Paniculata (14 spe-cies), with one species in the southwestern part ofsouthern Africa (Goldblatt & Manning, 1992), andsection Fastigiata (5 species), which is restricted SThis research was supported by National Geographic Society Grant 4816-92. We thank Peter Hoch, Jorge Crisci,D. Snijman, and A. de Villiers for helpful comments during the preparation of this paper. and Jennifer Hedin forrunning the bootstrap analyses. 2 B. A. Krukoff Curator of African Botanv. Missouri Botanical Garden. PO. Box 299. St. Louis. Missouri 63166-0299, U.S.A. " Compton Herbarium, National Botanical Institute. Kirstenbosch Botanic Gardens, Claremont 7735, South Africa.ANN. MISSOUtRI BOT. GARD. 83: 346-361. 1996.