Abstract
ABSTRACT This work aimed to morphologically characterize 22 species of Spermacoceae s.s found in the Atlantic Forest in the state of Rio de Janeiro with the purpose of improving palynological knowledge of the studied species. The studied species included six species of Borreria and Denscantia cymosa, Emmeorhiza umbellata, Hexasepalum apiculatum, H. radula, H. teres, Manettia fimbriata, Mitracarpus eichleri, M. frigidus, M. hirtus, M. lhotzkyanus, M. megapotamicus, Oldenlandia salzmannii, Pentodon pentandrus, Richardia brasiliensis, Richardia scabra and Spermacoce rubescens. Acetolysed pollen grains were analyzed using light (LM) and scanning electron miscroscopy (SEM). The pollen grains varied in size (polar diameter) from medium to large, with the exception of Hexasepalum teres which was very large. Pollen grains were oblate spheroidal in most species, suboblate in six species, prolate spheroidal in Spermacoce rubescens and subprolate in Manettia fimbriata. All pollen grains were colporate, while number of apertures varied (three-19). The endoaperture was lolongate in most species and lalongate in four species. Sexine ornamentation varied among reticulate, reticulate-granulate, microreticulate, granulate with perforation, echinate-perforate and vermiculate. Pollen attributes were found to distinguish the studied species, but do not separate genera, confirming that Spermacoceae is euripolynic.
Highlights
According to Angiosperm Phylogeny Group (APG IV 2016), Rubiaceae is positioned in the order Gentianales and recent phylogenetic studies have suggested support for only three subfamilies: Cinchonoideae Raf., Ixoroideae Raf. and Rubioideae Verdc
As for the shape, the pollen grains ranged from suboblate, oblate spheroidal, subprolate to prolate spheroidal
The genus Borreria was palynologically described in several studies, among those is the study by SalgadoLabouriau (1973) that, through the species B. capitata, established the Borreria type as zonoaperturate, with sixeight pores and sexine retipilate; Carreira (1976) described the pollen grains as small, six-seven-pantoporate, retipilate sexine
Summary
According to Angiosperm Phylogeny Group (APG IV 2016), Rubiaceae is positioned in the order Gentianales and recent phylogenetic studies have suggested support for only three subfamilies: Cinchonoideae Raf., Ixoroideae Raf. and Rubioideae Verdc. It is a cosmopolitan, predominantly pantropical family (Taylor et al 2007). The Spermacoceae s.s. is monophyletic tribe belongs the subfamily Rubioideae is one of the most representative tribes in Brazil, about 11 genera and 30 species are registered in the state of Rio de Janeiro (Flora do Brasil 2020 2019).
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