Re-evaluation of the taxonomic status of Hackelochloa (Poaceae) based on anatomical and phenetic analyses

Abstract

Hackelochloa is a pantropical genus of plant in the Poaceae, in which only two species have been included, H. granularis and H. porifera. Despite several morphological differences, notably the more prominent sculpturing of the lower glume and the larger dimensions of several quantitative traits, H. porifera has been reduced to the synonymy of H. granularis. Moreover, the status of the genus itself has been questioned, with a regional revision of the genus proposing inclusion of its members in the genus Mnesithea. In the present study, we investigated a range of morphological and anatomical attributes to assess critically the generic delimitation between Hackelochloa and Mnesithea. In clustering analysis, H. granularis, H. porifera and Mnesithea species were clearly resolved as three distinct groups with an R-value of 0.98114. Likewise, three clusters representing these taxonomic units were revealed using principal component analysis (PCA), with the first two principal components highlighting key qualitative and quantitative characters. Scanning electron microscopy was used to reveal different patterns of sculpturing on the lower glumes in the two putative species and the ecological significance of these differences is inferred. The outline of leaf transverse sections, presence of parenchymatous tissue in the midrib region, number of adjacent bundles and number of chlorenchyma layers in the culm were also found to be diagnostic anatomical characters. This study supports the recognition of H. porifera as distinct from H. granularis and provides evidence that the genus Hackelochloa should be maintained.