A study on the floral ontogeny in Caesalpinia gilliesii (Hook). Dietr and its comparison with other species of Caesalpinia

Abstract

Comparative floral ontogeny provides new characters for phylogenetic studies. Such studies have been useful for better understanding of floral evolution within the subfamilies of Fabaceae. However, the significance of floral ontogenetic data for evaluation of systematic position among different species of a genus has not yet been demonstrated. The aim of this study was to present a complete ontogenetic pathway of Caesalpinia gilliesii, as a member of Caesalpinioideae and to compare the results with other studied species of the genus. For this purpose, flower buds of different ages were collected and fixed in FAA. After a fixation period of 24 h, the samples were rinsed, dissected in 70% ethanol and further dehydrated in 95% ethanol prior to being stained with 0.5% nigrosin black in ethanol. The results showed that differences between ontogenetic pathways of Caesalpinia species were prominent and mostly appeared early in development. In C. gilliesii all whorls initiated unidirectionally except for petals that appeared bidirectionally. Different orders of sepal initiation have been reported for other studied species including helical, tendency towards whorl and modified unidirectional. In contrast to other studied species, C. gilliesii showed overlap in the time of initiation between different whorls. Unidirectional order of initiation and overlap of organ initiation were both advanced characters that distinguished C. gilliesii from other studied species of Caesalpinia.

Keywords

• Caesalpinia gilliesii
• Unidirectional initiation
• Floral ontogeny
• Overlap