Palynomorphic Characteristics of the Heteroblastic Inflorescence, Lamium amplexicaule L.: A Case Study

IN EGYPT, the genus Lamium L. (Family Lamiaceae) is represented by L. amplexicaule L., which possesses a heteroblastic inflorescence in which two breeding systems coexist. These two breeding systems are the cleistogamous system that processes self-pollinated, closed flower (CL) and the chasmogamous system with cross-pollinated, opened flower (CH). Although the pollen grains of the family Lamiaceae and Lamium spp. have been extensively investigated, the palynomorphological data distinguishing the pollen features for the CL and CH flowers are still lacking. This study aimed to (1) add more information about the palynomorphology of CL and CH flowers; (2) investigate the similarities and differences in palynomorphology between the pollen of these two flower types; in the same and different L. amplexicaule morphs. Our results showed that the heteroblastic inflorescence in L. amplexicaule L. in Egypt was represented by five pollen grain types. The scanning electron microscopy (SEM) results showed that all the pollen grain types were monads, tri-zonocolpate, isopolar, radially-symmetrical and reticulate, or microreticulate sculpture. The colpus length/colpus width ratios, P/E, apocolpium, and mesocolpium widths in the studied heteroblastic inflorescence were significantly different in the CL and CH flowers in the same and different morphs. The present study developed a key differentiating the five pollen grain types. In conclusion, this study confirms that the pollen characteristics were significantly different between and among the CL and CH flowers that coexist in the heteroblastic inflorescences of L. amplexicaule; this feature requires future clarification in different taxa.