PHYLOGENY AND SPECIATION IN LAPEIROUSIA SUBGENUS LAPEIROUSIA (IRIDACEAE, IXIOIDEAE)

A cladistic analysis of southern African subgenus Lapeirousia, one of two subgenera of the exclusively African genus Lapeirousia, yielded fo ur equally parsimonious trees, one of which is identical with the stri ct consensus tree. Characters used in the analysis included growth for m, corm morphology, a range of floral characters, and capsule and seed features, not before known to vary significantly in this genus. The a nalysis suggested some surprising evolutionary changes. Notable among these is an apparent reversal of perianth tube length from extremely l ong to short, a shift corresponding to a change from pollination by lo ng-tongued flies and sphinx moths to pollination by bees and noctuid m oths. Another unusual change is a shift in floral organization from zy gomorphy to actinomorphy correlated with an acaulescent growth form. T he reconstructed phylogeny is used here to assess character evolution and patterns of speciation by comparison of species in terminal clades in the cladograms. The resulting comparisons suggest that speciation in the subgenus is either-allopatric or the result of microgeographic differentiation and ecological diversification stimulated by edaphic d iversity. Despite the variety of floral forms and pollination syndrome s in the subgenus there is no evidence of sympatric or pollinator-driv en speciation. Prepollination reproductive isolation appears to be ach ieved by shifts in pollination syndromes between sphinx moths, two gui lds of long-tongued flies, and bees. The remarkable floral divergence that has resulted appears to be a consequence of selection for repeate d entry into preexisting pollination guilds. The most important of the se pollination guilds are two long-tongued Ay guilds in which either P rosoeca (Nemestrinidae) or Moegistorhynchus (Nemestrinidae) and Philol iche (Tabanidae) are pollinators. These two guilds are also likely to have been important in promoting speciation in other genera and famili es in the southern African flora.