Pollen Morphology and a New Combination in Tribe Justicieae (Acanthaceae), with Emphasis on Brazilian Species

Justicieae is one of the largest tribes of Acanthaceae, composed of 2000 species distributed in 100 genera, with highest diversity in the neotropical region. Palynological studies containing several representatives of the tribe are rare, specially species from Northeastern Brazil. The present study aims to differentiate species and evaluate palynological characters in the light of a phylogenetic hypothesis of Justicieae. Eighteen species belonging to six genera were analyzed. Pollen grains were acetolyzed, measured and photographed under light microscopy (LM) and scanning electron microscopy (SEM). Pollen grains are medium to very large in size, isopolar, planaperturate, subprolate, prolate to prolate spheroidal, and two-colporate to three-colporate, or with six pseudocolpi. The exine ornamentation is microreticulate to reticulate with areolae between the apertures in most species. Some species present a cavea in the mesocolpium. The pollen morphology of Justicia chamaedryoides, J. congrua, J. glaziovii, J. thunbergioides, J. sphaerosperma, Pseuderanthemum congestum, and P. modestum are hereby described for the first time. A new combination is also proposed, Thyrsacanthus angustissimus.