Micro-morphological features of Arundinelleae (Poaceae, Panicoideae) and their taxonomic significance

Arundinelleae is a taxonomically challenging tribe within Poaceae consisting of two genera. In this study, we examine micro-morphological features of lemmas and pollen for 35 taxa from Arundinelleae. Scanning electron microscopy was employed to assess the taxonomic significance of these morphological characters. The structural details of long and short cells, stomata, micro-hairs, macro-hairs, the distribution of prickles on the lemmas, and characteristics of pollen grains are described and illustrated, and their taxonomic significance is evaluated. The presence or absence of epicuticular waxes and prickle distribution are key characters for classification within Arundinelleae. Within Arundinella, some species can be reliably distinguished by the shape of long-cell walls and the distribution range of prickles on the lemma. While in Garnotia, variation in lemma long-cell wall morphology serves as an important diagnostic feature. Pollen morphological characteristics (including grain size, annulus, operculum, exine ornamentation, and aperture diameter) show some variation among Arundinelleae. Although these latter features provide limited taxonomic utility for delimiting tribes and genera, they enrich the Poaceae palynological dataset.