Palynotaxonomy of Leptohyptis Harley & J.F.B.Pastore and Oocephalus (Benth.) Harley & J.F.B.Pastore (Lamiaceae: Hyptidinae)

Abstract

This paper aims to characterize the pollen of two genera within the subtribe Hyptidinae (Lamiaceae): Leptohyptis Harley & J.F.B. Pastore (4 species) and Oocephalus (Benth.) Harley & J.F.B. Pastore (12 species). The study evaluates whether pollen morphology corroborates the recent taxonomy of the group. Acetolysed pollen grains were measured, described, and photomicrographed. Non-acetolysed pollen grains were analyzed by scanning electron microscopy. All analyzed taxa have pollen grains shed in monads, isopolar, medium or large in size, 6-(8)-colpate, varying from suboblate to prolate, with small to very small polar area. The presence of an operculum was observed in all species of Leptohyptis. By contrast, in Oocephalus, an operculum was present only O. grazielae Harley and O. niveus (Epling) Harley & J.F.B.Pastore. The sexine is reticulate in Leptohyptis and bireticulate with ornamented lumina in Oocephalus, being densely reticulate internally. The muri are straight, with or without elevations at the intersections, forming wide and circular lumina or small lumina, as in O. halimifolius (Mart. ex Benth.) Harley & J.F.B.Pastore. The variations revealed by this study imply that pollen morphology holds significant taxonomic value for the systematics of the genera Oocephalus and Leptohyptis, particularly when morphometric and morphological characters are examined together. Assessment of quantitative values ​​by multivariate analyses (hierarchical cluster analysis and principal component analysis) was not sufficient to separate the genus Oocephalus into its four sections. Only O. niveus and O. petraeus (A.St.-Hil. ex Benth.) Harley & J.F.B.Pastore remained separated. All other species remained in the same main group in hierarchical clustering, and it was also not possible to group L. calida (Mart. ex Benth.) Harley & J.F.B.Pastore with other species of the genus. The results revealed the existence of polymorphism in pollen shape among the studied taxa.