A new tetraploid species of Tacinga (Cactaceae) from Ceará, Northeastern Brazil

Abstract

A new species of cactus, Tacinga mirim (Cactaceae: Opuntioideae), is described and illustrated. Tacinga mirim is like a miniature version of T. palmadora, as far as is known, endemic to the state of Ceará, Northeastern Brazil. Although some populations of the new species have been known since 2009, they had been wrongly identified as T. palmadora. The description of the new species was made based on morphological and karyotypic analysis. Morphologically, it differs from T. palmadora by the much smaller size, semi-prostrate habit, smaller and deciduous stem-segments, lower density of spines, slightly larger and wide-open flowers, smooth pericarpel, and the globose to obovoid, purplish ripe fruit. The karyotype of T. mirim differs from T. palmadora in being tetraploid (not diploid), by presenting chromosomes that are twice as large, eight of which are submetacentric (differing from the fully metacentric standard karyotype of T. palmadora). The distribution of the new species is associated with the Caatinga of the crystalline basement of the northwestern hinterland of Ceará, found at relatively low altitudes (190-360 m). The IUCN category of threat for the new taxon was preliminary assessed. Both EOO and AOO indicate that the species is endangered (EN-B1-2ab).