Carajasia (Rubiaceae), a new and endangered genus from Carajás mountain range, Pará, Brazil

Abstract

Carajasia is described as a new genus of Rubiaceae. It is so far known only from the mountain summits of Serra dos Carajás (Pará, Brazil), where it is part of a shrubby vegetation surrounded by tropical rainforest. The new genus belongs to the tribe Spermacoceae and is positioned within it to the Spermacoce clade. Carajasia is unique within the clade in having a very particular combination of characters: flowering branches with two axillary flowers per node, homostylous flowers, corollas with a fringe of moniliform hairs, pubescent styles with distinct stigma lobes, bilobed nectariferous discs covered by triangular papillae, pollen with a double reticulum and fruits with a peculiar type of dehiscence. A detailed description of Carajasia is presented, including observations of the fruit and pollen, along with distribution maps and images of the plant in its habitat. A dichotomous key to distinguish Carajasia from other genera with deeply divided stigmas is provided. A molecular phylogenetic study was carried out using ITS and ETS sequences to determine the phylogenetic position of the new genus within the Spermacoce clade. The results of the combined analyses demonstrated that Carajasia is sister to Galianthe with moderate to high support. Both genera form a weakly supported clade with Schwendenera. This clade is sister to the other genera of the Spermacoce clade studied in this work. Galianthe and Schwendenera share with Carajasia pollen with a double reticulum, but they are clearly differentiated by suffruticose habit, heterostylous flowers and the pattern of fruit dehiscence. To clarify the phylogenetic position of Carajasia, some morphological characters are discussed based on the molecular results: division of the stigma, pollen types and floral syndrome.

Flora das cangas da Serra dos Carajás, Pará, Brasil: Rubiaceae

“…Mericarpos indeiscentes separando-se ao longo do septo, sementes planoconvexas, sem alas, face ventral levemente sulcada, testa reticulada. Gênero monotípico descrito recentemente, é conhecido apenas da FLONA de Carajás, em ambiente campestre (Salas et al 2015). Figs.…”

Brasilianthus (Melastomataceae), a new monotypic genus endemic to ironstone outcrops in the Brazilian Amazon

“…The flora of the forest and the canga uplands is diverse but it is imperfectly known and still being explored. The canga habitats, in particular, represent a unique isolated ecosystem in the Amazon and in Minas Gerais, Brazil, with high biodiversity and notable endemism (Jacobi et al 2007;Vincent & Meguro 2008;Golder Associates Brasil 2010;Oliveira et al 2014;Skirycz et al 2014;Piló et al 2015;Salas et al 2015).…”

A synopsis of Galianthe (Rubiaceae) in Rio Grande do Sul, Southern Brazil, and a new endemic species from Serra Geral

“…Recent molecular phylogenetic studies have demonstrated that Galianthe (Rubiaceae) belongs to the Spermacoce clade (Kårehed et al 2008;Salas et al 2015), is monophyletic and is most closely relate to Carajasia and Schwendenera, with both sharing the presence of pollen grains with a double reticulum (Salas et al 2015). e genus is Neotropical, with the exception of a single taxon living in Mesoamerica (G.brasiliensis subsp.…”

“…e species occur in campos rupestres (quartzitic rock outcrops), cerrado (savanna), low land grasslands, campos de altitude (highland grasslands), caatinga vegetation (seasonaly dry tropical forests) and savanna hillsides; in lateritic, sandy soils or with rock outcrops. Exceptionally, there are some shade-loving species, which occur in the understory of forests and woodlands, such as G. hispidula, G. brasiliensis, and G. laxa (Cabral & Bacigalupo 1997;Cabral 2009;Cabral & Salas 2015;Carmo et al 2016). Galianthe comprises 50 species grouped in two subgenera: Galianthe subg.…”