Taxonomic importance of the palynological features of some members of family Leguminosae-Caesalpinioideae
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.
Keywords: Pollen grains, Cassia, Senna, Aperturate, Monocolporate, Tricolpate