Pollen grains from fresh anthers of three species and a variety of Ocimum occurring in Southwestern Nigeria were collected and acetolysed. This was in an attempt to use the pollen characteristics to delimit, classify and trace probable evolutionary relationships among the taxa. The structural morphology of the pollen grains carried out with a light microscope is reported. Characters measured on the pollen grains were pollen diameter, pollen wall thickness, depth of colpi, distance between colpi and pore diameter. This was done with the aid of an ocular micrometer. Number of pores per pollen was counted. Pollen grain sizes of the species and the variety of Ocimum studied fall into two groups, Media (diameter 25-50µm) and Magna (diameter 50-100µm). All the species and the variety had acolpate and hexacolpate pollen grains. Heptacolpate and octacolpate pollen grains which are advanced types of pollen grains were encountered in O. canum only. These advanced types of pollen grains are a mark of recent evolutionary development in the species.

Acetolysed pollen grains of eight species in the Leguminosae-Caesalpinioideae were studied with the aim of identifying palynological characters of taxonomic importance among the taxa and determining their probable evolutionary relationships. The Acetolysis procedure and pollen type description were carried out following standard methods. The eight species include two species from genus Cassia Linn.-Cassia sieberiana DC and Cassia fistula Linn and six species from genus Senna Mill.-Senna occidentalis (Linn.) Link, Senna siamea (Lam.) Irwin and Barneby, Senna podocarpa (Guill. & Perr.) Lock, Senna hirsuta (Linn.) Irwin and Barneby, Senna obtusifolia (L.) Irwin and Barneby and Senna sophera (L.) Roxb. The pollens of all the species were shed as monads and they all had perforate sculpturing pattern on their exine. The pollen size of all the species falls into the group media (25-50 µm). All the species had ovate pollen shapes except for some additional circular, elliptic and club-shaped types observed in some of the species. All the species had monocolporate and tricolpate pollen grain types. Tetracolpate, pentacolpate and hexacolpate pollen grains, which are advanced pollen types were observed only in the species of Senna while the primitive pollen types, acolpate and monocolpate, were observed more in the members of the genus Cassia, thus, the evolutionary advancement of Senna over Cassia was discussed. Other pollen types observed in some of the species were bicolpate, trilete, diporate, tricolporate, and pentacolporate. Their importance in the identification and classification of the Cassia and Senna species was also discussed.