CHROMOSOME CYTOLOGY IN TROPICAL AFRICAN GLADIOLUS (IRIDACEAE)

Original chromosome counts for 16 species of tropical African Gladiolu s, 5 southern African, and 3 Eurasian species, 17 of these not before examined, confirm that x = 15 is probably the ancestral basic number f or the genus. Until now, x = 15 has been the only recorded base number in Gladiolus, but several tropical African species have been found to depart from this pattern, the only known examples of dysploidy in the genus. In subgenus Gladiolus, G. atropurpureus has x = 12 (2n = 24 0-5B, 36); G. serapiflorus, G. gregarius, and G. pseudospicatus have x = 11 (2n = 22); G. unguiculatus has x = 13 (2n = 26 + 0-2B, also poss ibly 2n = 24); and G. actinomorphanthus has 2n = 28. Because on morpho logical grounds most of these species do not seem to be immediately re lated, we suggest that dysploid reduction in tropical African Gladiolu s may have occurred in four separate lineages. Results confirm polyplo idy in G. dalenii, 2n = 60 and 90, and the three Eurasian species exam ined. The first count for the Malawian G. bellus, 2n = 60, indicates p olyploidy in only one more tropical African species of Gladiolus. Coun ts of 2n = 39 in two populations of G. decoratus suggest triploidy bas ed on x = 13, making this one more possible example of dysploidy for t he genus. Although the chromosomes of Gladiolus are relatively small, some karyotypic details provide additional data relating to species re lationships. Measurements of total chromosome length show that irrespe ctive of base number, most of the diploid species have a comparable am ount of chromosome material. Two species, G. melleri (2n = 30) and G. decoratus (2n = 39), however, have significantly higher amounts of chr omosome material, ca. 33-40% above expected levels, a condition possib ly related to their characteristic rapid growth and flowering early in the growing season.