CYTOLOGICALVARIABILITY IN THEAFRICAN GENUSLAPEIROUSIA(IRIDACEAE-IXIOIDEAE)1Peter Goldblatt2ABSTRACT The African genus Lapeirousia (Iridaceae-lxioideae) comprises two subgenera each with two sections. The basicchromosome number for the genus is postulated to be x = 10 in a strongly bimodal karyotype with one long andnine much smaller pairs. This karyotype occurs in at least some species of three sections and is exclusive in subg.Paniculata Goldbl. & Manning sect. Fastigiata Goldbl. In subg. Lapeirousia the bimodality is preserved in ailspecies, but chromosome number ranges from n = 10 to 8. Genera most closely allied to Lapeirousia also have x= 10 and asymmetric but less strongly bimodal karyotypes. Sect. Paniculata, which is entirely tropical in distribution,has species with n = 8, 7, 6, 5, 4, and 3. Species of the section with the highest chromosome numbers have bimodalkaryotypes with one longer chromosome pair. Total chromosome length, a crude measure of genome size, is similarin ail except two species, which have n = 6 and approximately twice the total chromosome length compared with ailother species examined. Polyploidy appears to have been involved in the evolution of only these two species. Dysploidreduction is thought to have been responsible for the variation in chromosome number noted in other species. Evidencefrom comparative morphology suggests that descending dysploidy occurred repeatedly in the genus and that lownumbers, n = 4 and 3, were achieved in separate lineages. Lapeirousia Pourret, a genus of Iridaceae-Ixioideae (cf. Goldblatt, 1990a), comprises some35 species (Goldblatt, 1972, 1990b; Goldblatt &Manning, 1990) distributed in two subgenera eachwith two sections. The genus is widespread in Africasouth of the Sahara, with centers in the winter-rainfall zone of the southern African west coastand in the drier parts of tropical Africa, particularlyNamibia. This pattern is unusual for Iridaceae, inwhich most African genera are either restricted tothe Cape region of South Africa or extend into thewetter parts of eastern southern Africa, some asfar north as Ethiopia. Only Gladiolus (Ixioideae),Moraea (Iridoideae), and Aristea (Nivenioideae)have ranges comparable to Lapeirousia, but theyare absent or poorly represented in areas of tropicalAfrica where Lapeirousia is best developed (Gold-blatt, 1990b). Chromosome cytology of Lapeirousia in south-ern Africa in moderately well documented, withnine species counted, about half the total (Goldblatt,1971, 1972), but until now there have been nocounts for any tropical African species. The karyo-types of 13 species in tropical Africa (of a total of16) and an additional seven in southern Africa aredescribed here. The cytology of only five speciesremains unknown. Data indicate that Lapeirousiais unusually variable cytologically. Haploid num-bers of n = 10, 9, 8, 7, 6, 5, 4, and 3 have nowbeen recorded in the genus. This contrasts withthe majority of Ixioideae, which are cytologicallyuniform (Goldblatt, 1971) and typically have onlyone base number and relatively little polyploidy.Only Romulea and Crocus have until now beenexceptions to this pattern in the subfamily (De Vos,1972; Brighton, 1976a, b, 1977). Variation in chromosome number in Lapeirou-sia is accompanied by major differences in karyo-type. Strong bimodality appears to be the rule(Goldblatt, 1972), with one long chromosome pairand a variable number of much smaller pairs (Gold-blatt, 1971, 1972). The bimodality encounteredin ail southern African species examined also oc-curs in some of the tropical species. The patterns Support for this study by grant BSR 85-00148 from the U.S. National Science Foundation and grant 3749-88from the National Geographic Society is gratefully acknowledged. I thank the following for their help in obtaininglive material of species of Lapeirousia: Jean Pawek, San Jose, California; Georges Delpierre, Durbanville, SouthAfrica; J. W. Loubser, Strand, South Africa; Maurice Boussard, Verdun, France; Jan de Koning, Maputo, Mozambique;Isobyl la Croix, Gairloch, Scotland; Sylvester Chisumpa, Kitwe, Zambia; and W. Giess, Windhoek, Namibia. 2 B. A. Krukoff Curator of African Botany, Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166,U.S.A.ANN. MISSOURI BOT. GARD. 77: 375-382. 1990.