Pollen morphology of origanum L. (Lamiaceae)

Abstract

It has been known for many years that the pollen morphology of the Lamiaceae family is systematically important. The Lamiaceae family is divided into two large subfamilies according to their palynological characteristics, considering the nucleus and aperture numbers. The genus Origanum L., whose pollen morphologies were examined in this study, is placed in the Nepetoideae subfamily. Although many studies have been conducted on the pollen morphology of the Lamiaceae, the number of studies on hybrid species in the Lamiaceae is very small. This chapter focuses on the 17 taxa of Origanum that include some hybrids. The pollen morphology of the 17 taxa was studied in detail using light microscope and scanning electron microscope observations. According to the investigations, pollen grains are isopolar, hexacolpate; amb shape circular, pollen shape from oblate spheroidal to prolate spheroidal, colpus membrane granular or nongranular, exine ornamentation reticulate or bireticulate. Colpus length varies between 8.61-27.73 μm. Colpi are narrow or wide, long with distinct borders, and the colpus membrane is granular in many taxa. Exine thickness was measured as 0.4-1.01 μm. Intine thickness was determined as 0.29-0.70 μm. The mesocolpial area varies from 5.92 μm to 13.28 μm. In some taxa, the exine ornamentation in the apocolpium differs from the exine ornamentation in the mesocolpium with primary muri, long or angular. Primary muri do not show continuity in some taxa. The primary reticulum in the apocolpial area and mesocolpium may differ in size or perforate ornamentation. It was determined that the polar axis varied between 13.41-34.01 μm. The polar axis was determined as the shortest in O. × haradjanii Rech.f. and the longest in O. saccatum P.H. Davis. The equatorial diameter varies between 12.58-36.43 μm. P / E ratio ranges from 0.78-1.07. A positive correlation was observed between the polar axis and equatorial diameter length. A taxonomically significant positive correlation (0.956; 0.001) was determined between P and E, and polar axis and colpus length were also found to be significantly positive (0.936; 0.01). Similarly, mesocolpial and apocolpial areas show a positive correlation with polar axis and equatorial diameter lengths. In conclusion, pollen morphology studies in the genus Origanum so far indicate that additional sources of potentially very useful characters are available.